path: root/meta/recipes-devtools/gcc/gcc/0001-CVE-2021-42574.patch

From 004bb936d6d5f177af26ad4905595e843d5665a5 Mon Sep 17 00:00:00 2001
From: Lewis Hyatt <lhyatt@gmail.com>
Date: Tue, 14 Jul 2020 12:05:56 -0400
Subject: [PATCH] diagnostics: Support conversion of tabs to spaces [PR49973]
 [PR86904]

Supports conversion of tabs to spaces when outputting diagnostics. Also
adds -fdiagnostics-column-unit and -fdiagnostics-column-origin options to
control how the column number is output, thereby resolving the two PRs.

gcc/c-family/ChangeLog:

	PR other/86904
	* c-indentation.c (should_warn_for_misleading_indentation): Get
	global tabstop from the new source.
	* c-opts.c (c_common_handle_option): Remove handling of -ftabstop, which
	is now a common option.
	* c.opt: Likewise.

gcc/ChangeLog:

	PR preprocessor/49973
	PR other/86904
	* common.opt: Handle -ftabstop here instead of in c-family
	options.  Add -fdiagnostics-column-unit= and
	-fdiagnostics-column-origin= options.
	* opts.c (common_handle_option): Handle the new options.
	* diagnostic-format-json.cc (json_from_expanded_location): Add
	diagnostic_context argument.  Use it to convert column numbers as per
	the new options.
	(json_from_location_range): Likewise.
	(json_from_fixit_hint): Likewise.
	(json_end_diagnostic): Pass the new context argument to helper
	functions above.  Add "column-origin" field to the output.
	(test_unknown_location): Add the new context argument to calls to
	helper functions.
	(test_bad_endpoints): Likewise.
	* diagnostic-show-locus.c
	(exploc_with_display_col::exploc_with_display_col): Support
	tabstop parameter.
	(layout_point::layout_point): Make use of class
	exploc_with_display_col.
	(layout_range::layout_range): Likewise.
	(struct line_bounds): Clarify that the units are now always
	display columns.  Rename members accordingly.  Add constructor.
	(layout::print_source_line): Add support for tab expansion.
	(make_range): Adapt to class layout_range changes.
	(layout::maybe_add_location_range): Likewise.
	(layout::layout): Adapt to class exploc_with_display_col changes.
	(layout::calculate_x_offset_display): Support tabstop parameter.
	(layout::print_annotation_line): Adapt to struct line_bounds changes.
	(layout::print_line): Likewise.
	(line_label::line_label): Add diagnostic_context argument.
	(get_affected_range): Likewise.
	(get_printed_columns): Likewise.
	(layout::print_any_labels): Adapt to struct line_label changes.
	(class correction): Add m_tabstop member.
	(correction::correction): Add tabstop argument.
	(correction::compute_display_cols): Use m_tabstop.
	(class line_corrections): Add m_context member.
	(line_corrections::line_corrections): Add diagnostic_context argument.
	(line_corrections::add_hint): Use m_context to handle tabstops.
	(layout::print_trailing_fixits): Adapt to class line_corrections
	changes.
	(test_layout_x_offset_display_utf8): Support tabstop parameter.
	(test_layout_x_offset_display_tab): New selftest.
	(test_one_liner_colorized_utf8): Likewise.
	(test_tab_expansion): Likewise.
	(test_diagnostic_show_locus_one_liner_utf8): Call the new tests.
	(diagnostic_show_locus_c_tests): Likewise.
	(test_overlapped_fixit_printing): Adapt to helper class and
	function changes.
	(test_overlapped_fixit_printing_utf8): Likewise.
	(test_overlapped_fixit_printing_2): Likewise.
	* diagnostic.h (enum diagnostics_column_unit): New enum.
	(struct diagnostic_context): Add members for the new options.
	(diagnostic_converted_column): Declare.
	(json_from_expanded_location): Add new context argument.
	* diagnostic.c (diagnostic_initialize): Initialize new members.
	(diagnostic_converted_column): New function.
	(maybe_line_and_column): Be willing to output a column of 0.
	(diagnostic_get_location_text): Convert column number as per the new
	options.
	(diagnostic_report_current_module): Likewise.
	(assert_location_text): Add origin and column_unit arguments for
	testing the new functionality.
	(test_diagnostic_get_location_text): Test the new functionality.
	* doc/invoke.texi: Document the new options and behavior.
	* input.h (location_compute_display_column): Add tabstop argument.
	* input.c (location_compute_display_column): Likewise.
	(test_cpp_utf8): Add selftests for tab expansion.
	* tree-diagnostic-path.cc (default_tree_make_json_for_path): Pass the
	new context argument to json_from_expanded_location().

libcpp/ChangeLog:

	PR preprocessor/49973
	PR other/86904
	* include/cpplib.h (struct cpp_options):  Removed support for -ftabstop,
	which is now handled by diagnostic_context.
	(class cpp_display_width_computation): New class.
	(cpp_byte_column_to_display_column): Add optional tabstop argument.
	(cpp_display_width): Likewise.
	(cpp_display_column_to_byte_column): Likewise.
	* charset.c
	(cpp_display_width_computation::cpp_display_width_computation): New
	function.
	(cpp_display_width_computation::advance_display_cols): Likewise.
	(compute_next_display_width): Removed and implemented this
	functionality in a new function...
	(cpp_display_width_computation::process_next_codepoint): ...here.
	(cpp_byte_column_to_display_column): Added tabstop argument.
	Reimplemented in terms of class cpp_display_width_computation.
	(cpp_display_column_to_byte_column): Likewise.
	* init.c (cpp_create_reader): Remove handling of -ftabstop, which is now
	handled by diagnostic_context.

gcc/testsuite/ChangeLog:

	PR preprocessor/49973
	PR other/86904
	* c-c++-common/Wmisleading-indentation-3.c: Adjust expected output
	for new defaults.
	* c-c++-common/Wmisleading-indentation.c: Likewise.
	* c-c++-common/diagnostic-format-json-1.c: Likewise.
	* c-c++-common/diagnostic-format-json-2.c: Likewise.
	* c-c++-common/diagnostic-format-json-3.c: Likewise.
	* c-c++-common/diagnostic-format-json-4.c: Likewise.
	* c-c++-common/diagnostic-format-json-5.c: Likewise.
	* c-c++-common/missing-close-symbol.c: Likewise.
	* g++.dg/diagnostic/bad-binary-ops.C: Likewise.
	* g++.dg/parse/error4.C: Likewise.
	* g++.old-deja/g++.brendan/crash11.C: Likewise.
	* g++.old-deja/g++.pt/overload2.C: Likewise.
	* g++.old-deja/g++.robertl/eb109.C: Likewise.
	* gcc.dg/analyzer/malloc-paths-9.c: Likewise.
	* gcc.dg/bad-binary-ops.c: Likewise.
	* gcc.dg/format/branch-1.c: Likewise.
	* gcc.dg/format/pr79210.c: Likewise.
	* gcc.dg/plugin/diagnostic-test-expressions-1.c: Likewise.
	* gcc.dg/plugin/diagnostic-test-string-literals-1.c: Likewise.
	* gcc.dg/redecl-4.c: Likewise.
	* gfortran.dg/diagnostic-format-json-1.F90: Likewise.
	* gfortran.dg/diagnostic-format-json-2.F90: Likewise.
	* gfortran.dg/diagnostic-format-json-3.F90: Likewise.
	* go.dg/arrayclear.go: Add a comment explaining why adding a
	comment was necessary to work around a dejagnu bug.
	* c-c++-common/diagnostic-units-1.c: New test.
	* c-c++-common/diagnostic-units-2.c: New test.
	* c-c++-common/diagnostic-units-3.c: New test.
	* c-c++-common/diagnostic-units-4.c: New test.
	* c-c++-common/diagnostic-units-5.c: New test.
	* c-c++-common/diagnostic-units-6.c: New test.
	* c-c++-common/diagnostic-units-7.c: New test.
	* c-c++-common/diagnostic-units-8.c: New test.

CVE: CVE-2021-42574
Upstream-Status: Backport [https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=004bb936d6d5f177af26ad4905595e843d5665a5]
Signed-off-by: Pgowda <pgowda.cve@gmail.com>
---
 gcc/c-family/c-indentation.c                  |   5 +-
 gcc/c-family/c-opts.c                         |   6 -
 gcc/c-family/c.opt                            |   4 -
 gcc/common.opt                                |  21 +
 gcc/diagnostic-format-json.cc                 |  55 +-
 gcc/diagnostic-show-locus.c                   | 504 +++++++++++++-----
 gcc/diagnostic.c                              | 113 +++-
 gcc/diagnostic.h                              |  28 +-
 gcc/doc/invoke.texi                           |  68 ++-
 gcc/input.c                                   |  72 ++-
 gcc/input.h                                   |   4 +-
 gcc/opts.c                                    |  14 +
 .../c-c++-common/Wmisleading-indentation-3.c  |  12 +-
 .../c-c++-common/Wmisleading-indentation.c    |   6 +-
 .../c-c++-common/diagnostic-format-json-1.c   |   5 +
 .../c-c++-common/diagnostic-format-json-2.c   |   5 +
 .../c-c++-common/diagnostic-format-json-3.c   |   5 +
 .../c-c++-common/diagnostic-format-json-4.c   |   9 +
 .../c-c++-common/diagnostic-format-json-5.c   |   9 +
 .../c-c++-common/diagnostic-units-1.c         |  28 +
 .../c-c++-common/diagnostic-units-2.c         |  28 +
 .../c-c++-common/diagnostic-units-3.c         |  28 +
 .../c-c++-common/diagnostic-units-4.c         |  28 +
 .../c-c++-common/diagnostic-units-5.c         |  28 +
 .../c-c++-common/diagnostic-units-6.c         |  28 +
 .../c-c++-common/diagnostic-units-7.c         |  28 +
 .../c-c++-common/diagnostic-units-8.c         |  28 +
 .../c-c++-common/missing-close-symbol.c       |   6 +-
 .../g++.dg/diagnostic/bad-binary-ops.C        |   8 +-
 gcc/testsuite/g++.dg/parse/error4.C           |   2 +-
 .../g++.old-deja/g++.brendan/crash11.C        |   4 +-
 gcc/testsuite/g++.old-deja/g++.pt/overload2.C |   2 +-
 .../g++.old-deja/g++.robertl/eb109.C          |   4 +-
 .../gcc.dg/analyzer/malloc-paths-9.c          |   2 +-
 gcc/testsuite/gcc.dg/bad-binary-ops.c         |   8 +-
 gcc/testsuite/gcc.dg/format/branch-1.c        |   2 +-
 gcc/testsuite/gcc.dg/format/pr79210.c         |   2 +-
 .../plugin/diagnostic-test-expressions-1.c    |  16 +-
 .../diagnostic-test-string-literals-1.c       |   4 +-
 gcc/testsuite/gcc.dg/redecl-4.c               |   2 +-
 .../gfortran.dg/diagnostic-format-json-1.F90  |   5 +
 .../gfortran.dg/diagnostic-format-json-2.F90  |   5 +
 .../gfortran.dg/diagnostic-format-json-3.F90  |   5 +
 gcc/testsuite/go.dg/arrayclear.go             |   3 +
 gcc/tree-diagnostic-path.cc                   |   5 +-
 libcpp/charset.c                              |  98 ++--
 libcpp/include/cpplib.h                       |  40 +-
 libcpp/init.c                                 |   1 -
 48 files changed, 1106 insertions(+), 287 deletions(-)
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-1.c
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-2.c
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-3.c
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-4.c
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-5.c
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-6.c
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-7.c
 create mode 100644 gcc/testsuite/c-c++-common/diagnostic-units-8.c

diff --git a/gcc/c-family/c-indentation.c b/gcc/c-family/c-indentation.c
--- a/gcc/c-family/c-indentation.c	2020-07-22 23:35:17.296384022 -0700
+++ b/gcc/c-family/c-indentation.c	2021-12-25 01:20:53.475636694 -0800
@@ -24,8 +24,7 @@ along with GCC; see the file COPYING3.
 #include "c-common.h"
 #include "c-indentation.h"
 #include "selftest.h"
-
-extern cpp_options *cpp_opts;
+#include "diagnostic.h"
 
 /* Round up VIS_COLUMN to nearest tab stop. */
 
@@ -294,7 +293,7 @@ should_warn_for_misleading_indentation (
   expanded_location next_stmt_exploc = expand_location (next_stmt_loc);
   expanded_location guard_exploc = expand_location (guard_loc);
 
-  const unsigned int tab_width = cpp_opts->tabstop;
+  const unsigned int tab_width = global_dc->tabstop;
 
   /* They must be in the same file.  */
   if (next_stmt_exploc.file != body_exploc.file)
diff --git a/gcc/c-family/c.opt b/gcc/c-family/c.opt
--- a/gcc/c-family/c.opt	2021-12-24 20:23:42.816809230 -0800
+++ b/gcc/c-family/c.opt	2021-12-25 01:20:53.475636694 -0800
@@ -1876,10 +1876,6 @@ Enum(strong_eval_order) String(some) Val
 EnumValue
 Enum(strong_eval_order) String(all) Value(2)
 
-ftabstop=
-C ObjC C++ ObjC++ Joined RejectNegative UInteger
--ftabstop=<number>	Distance between tab stops for column reporting.
-
 ftemplate-backtrace-limit=
 C++ ObjC++ Joined RejectNegative UInteger Var(template_backtrace_limit) Init(10)
 Set the maximum number of template instantiation notes for a single warning or error.
diff --git a/gcc/c-family/c-opts.c b/gcc/c-family/c-opts.c
--- a/gcc/c-family/c-opts.c	2021-12-24 20:23:44.824774786 -0800
+++ b/gcc/c-family/c-opts.c	2021-12-25 01:20:53.475636694 -0800
@@ -504,12 +504,6 @@ c_common_handle_option (size_t scode, co
 	cpp_opts->track_macro_expansion = 2;
       break;
 
-    case OPT_ftabstop_:
-      /* It is documented that we silently ignore silly values.  */
-      if (value >= 1 && value <= 100)
-	cpp_opts->tabstop = value;
-      break;
-
     case OPT_fexec_charset_:
       cpp_opts->narrow_charset = arg;
       break;
diff --git a/gcc/common.opt b/gcc/common.opt
--- a/gcc/common.opt	2021-12-24 20:23:42.480814993 -0800
+++ b/gcc/common.opt	2021-12-25 01:20:53.475636694 -0800
@@ -1325,6 +1325,14 @@ Enum(diagnostic_url_rule) String(always)
 EnumValue
 Enum(diagnostic_url_rule) String(auto) Value(DIAGNOSTICS_URL_AUTO)
 
+fdiagnostics-column-unit=
+Common Joined RejectNegative Enum(diagnostics_column_unit)
+-fdiagnostics-column-unit=[display|byte]	Select whether column numbers are output as display columns (default) or raw bytes.
+
+fdiagnostics-column-origin=
+Common Joined RejectNegative UInteger
+-fdiagnostics-column-origin=<number>	Set the number of the first column.  The default is 1-based as per GNU style, but some utilities may expect 0-based, for example.
+
 fdiagnostics-format=
 Common Joined RejectNegative Enum(diagnostics_output_format)
 -fdiagnostics-format=[text|json]	Select output format.
@@ -1334,6 +1342,15 @@ SourceInclude
 diagnostic.h
 
 Enum
+Name(diagnostics_column_unit) Type(int)
+
+EnumValue
+Enum(diagnostics_column_unit) String(display) Value(DIAGNOSTICS_COLUMN_UNIT_DISPLAY)
+
+EnumValue
+Enum(diagnostics_column_unit) String(byte) Value(DIAGNOSTICS_COLUMN_UNIT_BYTE)
+
+Enum
 Name(diagnostics_output_format) Type(int)
 
 EnumValue
@@ -1362,6 +1379,10 @@ fdiagnostics-path-format=
 Common Joined RejectNegative Var(flag_diagnostics_path_format) Enum(diagnostic_path_format) Init(DPF_INLINE_EVENTS)
 Specify how to print any control-flow path associated with a diagnostic.
 
+ftabstop=
+Common Joined RejectNegative UInteger
+-ftabstop=<number>      Distance between tab stops for column reporting.
+
 Enum
 Name(diagnostic_path_format) Type(int)
 
diff --git a/gcc/diagnostic.c b/gcc/diagnostic.c
--- a/gcc/diagnostic.c	2020-07-22 23:35:17.556386887 -0700
+++ b/gcc/diagnostic.c	2021-12-25 01:23:41.300841207 -0800
@@ -38,6 +38,7 @@ along with GCC; see the file COPYING3.
 #include "selftest.h"
 #include "selftest-diagnostic.h"
 #include "opts.h"
+#include "cpplib.h"
 
 #ifdef HAVE_TERMIOS_H
 # include <termios.h>
@@ -219,6 +220,9 @@ diagnostic_initialize (diagnostic_contex
   context->min_margin_width = 0;
   context->show_ruler_p = false;
   context->parseable_fixits_p = false;
+  context->column_unit = DIAGNOSTICS_COLUMN_UNIT_DISPLAY;
+  context->column_origin = 1;
+  context->tabstop = 8;
   context->edit_context_ptr = NULL;
   context->diagnostic_group_nesting_depth = 0;
   context->diagnostic_group_emission_count = 0;
@@ -353,8 +357,51 @@ diagnostic_get_color_for_kind (diagnosti
   return diagnostic_kind_color[kind];
 }
 
+/* Given an expanded_location, convert the column (which is in 1-based bytes)
+   to the requested units, without converting the origin.
+   Return -1 if the column is invalid (<= 0).  */
+
+static int
+convert_column_unit (enum diagnostics_column_unit column_unit,
+		     int tabstop,
+		     expanded_location s)
+{
+  if (s.column <= 0)
+    return -1;
+
+  switch (column_unit)
+    {
+    default:
+      gcc_unreachable ();
+
+    case DIAGNOSTICS_COLUMN_UNIT_DISPLAY:
+      {
+	cpp_char_column_policy policy (tabstop, cpp_wcwidth);
+	return location_compute_display_column (s, policy);
+      }
+
+    case DIAGNOSTICS_COLUMN_UNIT_BYTE:
+      return s.column;
+    }
+}
+
+/* Given an expanded_location, convert the column (which is in 1-based bytes)
+   to the requested units and origin.  Return -1 if the column is
+   invalid (<= 0).  */
+int
+diagnostic_converted_column (diagnostic_context *context, expanded_location s)
+{
+  int one_based_col
+    = convert_column_unit (context->column_unit, context->tabstop, s);
+  if (one_based_col <= 0)
+    return -1;
+  return one_based_col + (context->column_origin - 1);
+}
+
 /* Return a formatted line and column ':%line:%column'.  Elided if
-   zero.  The result is a statically allocated buffer.  */
+   line == 0 or col < 0.  (A column of 0 may be valid due to the
+   -fdiagnostics-column-origin option.)
+   The result is a statically allocated buffer.  */
 
 static const char *
 maybe_line_and_column (int line, int col)
@@ -363,8 +410,9 @@ maybe_line_and_column (int line, int col
 
   if (line)
     {
-      size_t l = snprintf (result, sizeof (result),
-			   col ? ":%d:%d" : ":%d", line, col);
+      size_t l
+	= snprintf (result, sizeof (result),
+		    col >= 0 ? ":%d:%d" : ":%d", line, col);
       gcc_checking_assert (l < sizeof (result));
     }
   else
@@ -383,8 +431,14 @@ diagnostic_get_location_text (diagnostic
   const char *locus_cs = colorize_start (pp_show_color (pp), "locus");
   const char *locus_ce = colorize_stop (pp_show_color (pp));
   const char *file = s.file ? s.file : progname;
-  int line = strcmp (file, N_("<built-in>")) ? s.line : 0;
-  int col = context->show_column ? s.column : 0;
+  int line = 0;
+  int col = -1;
+  if (strcmp (file, N_("<built-in>")))
+    {
+      line = s.line;
+      if (context->show_column)
+	col = diagnostic_converted_column (context, s);
+    }
 
   const char *line_col = maybe_line_and_column (line, col);
   return build_message_string ("%s%s%s:%s", locus_cs, file,
@@ -650,14 +704,20 @@ diagnostic_report_current_module (diagno
       if (! MAIN_FILE_P (map))
 	{
 	  bool first = true;
+	  expanded_location s = {};
 	  do
 	    {
 	      where = linemap_included_from (map);
 	      map = linemap_included_from_linemap (line_table, map);
-	      const char *line_col
-		= maybe_line_and_column (SOURCE_LINE (map, where),
-					 first && context->show_column
-					 ? SOURCE_COLUMN (map, where) : 0);
+	      s.file = LINEMAP_FILE (map);
+	      s.line = SOURCE_LINE (map, where);
+	      int col = -1;
+	      if (first && context->show_column)
+		{
+		  s.column = SOURCE_COLUMN (map, where);
+		  col = diagnostic_converted_column (context, s);
+		}
+	      const char *line_col = maybe_line_and_column (s.line, col);
 	      static const char *const msgs[] =
 		{
 		 N_("In file included from"),
@@ -666,7 +726,7 @@ diagnostic_report_current_module (diagno
 	      unsigned index = !first;
 	      pp_verbatim (context->printer, "%s%s %r%s%s%R",
 			   first ? "" : ",\n", _(msgs[index]),
-			   "locus", LINEMAP_FILE (map), line_col);
+			   "locus", s.file, line_col);
 	      first = false;
 	    }
 	  while (! MAIN_FILE_P (map));
@@ -2042,10 +2102,15 @@ test_print_parseable_fixits_replace ()
 static void
 assert_location_text (const char *expected_loc_text,
 		      const char *filename, int line, int column,
-		      bool show_column)
+		      bool show_column,
+		      int origin = 1,
+		      enum diagnostics_column_unit column_unit
+			= DIAGNOSTICS_COLUMN_UNIT_BYTE)
 {
   test_diagnostic_context dc;
   dc.show_column = show_column;
+  dc.column_unit = column_unit;
+  dc.column_origin = origin;
 
   expanded_location xloc;
   xloc.file = filename;
@@ -2069,7 +2134,10 @@ test_diagnostic_get_location_text ()
   assert_location_text ("PROGNAME:", NULL, 0, 0, true);
   assert_location_text ("<built-in>:", "<built-in>", 42, 10, true);
   assert_location_text ("foo.c:42:10:", "foo.c", 42, 10, true);
-  assert_location_text ("foo.c:42:", "foo.c", 42, 0, true);
+  assert_location_text ("foo.c:42:9:", "foo.c", 42, 10, true, 0);
+  assert_location_text ("foo.c:42:1010:", "foo.c", 42, 10, true, 1001);
+  for (int origin = 0; origin != 2; ++origin)
+    assert_location_text ("foo.c:42:", "foo.c", 42, 0, true, origin);
   assert_location_text ("foo.c:", "foo.c", 0, 10, true);
   assert_location_text ("foo.c:42:", "foo.c", 42, 10, false);
   assert_location_text ("foo.c:", "foo.c", 0, 10, false);
@@ -2077,6 +2145,41 @@ test_diagnostic_get_location_text ()
   maybe_line_and_column (INT_MAX, INT_MAX);
   maybe_line_and_column (INT_MIN, INT_MIN);
 
+  {
+    /* In order to test display columns vs byte columns, we need to create a
+       file for location_get_source_line() to read.  */
+
+    const char *const content = "smile \xf0\x9f\x98\x82\n";
+    const int line_bytes = strlen (content) - 1;
+    const int def_tabstop = 8;
+    const int display_width = cpp_display_width (content, line_bytes,
+						 def_tabstop);
+    ASSERT_EQ (line_bytes - 2, display_width);
+    temp_source_file tmp (SELFTEST_LOCATION, ".c", content);
+    const char *const fname = tmp.get_filename ();
+    const int buf_len = strlen (fname) + 16;
+    char *const expected = XNEWVEC (char, buf_len);
+
+    snprintf (expected, buf_len, "%s:1:%d:", fname, line_bytes);
+    assert_location_text (expected, fname, 1, line_bytes, true,
+			  1, DIAGNOSTICS_COLUMN_UNIT_BYTE);
+
+    snprintf (expected, buf_len, "%s:1:%d:", fname, line_bytes - 1);
+    assert_location_text (expected, fname, 1, line_bytes, true,
+			  0, DIAGNOSTICS_COLUMN_UNIT_BYTE);
+
+    snprintf (expected, buf_len, "%s:1:%d:", fname, display_width);
+    assert_location_text (expected, fname, 1, line_bytes, true,
+			  1, DIAGNOSTICS_COLUMN_UNIT_DISPLAY);
+
+    snprintf (expected, buf_len, "%s:1:%d:", fname, display_width - 1);
+    assert_location_text (expected, fname, 1, line_bytes, true,
+			  0, DIAGNOSTICS_COLUMN_UNIT_DISPLAY);
+
+    XDELETEVEC (expected);
+  }
+
+
   progname = old_progname;
 }
 
diff --git a/gcc/diagnostic-format-json.cc b/gcc/diagnostic-format-json.cc
--- a/gcc/diagnostic-format-json.cc	2020-07-22 23:35:17.556386887 -0700
+++ b/gcc/diagnostic-format-json.cc	2021-12-25 01:20:53.475636694 -0800
@@ -23,6 +23,7 @@ along with GCC; see the file COPYING3.
 #include "system.h"
 #include "coretypes.h"
 #include "diagnostic.h"
+#include "selftest-diagnostic.h"
 #include "diagnostic-metadata.h"
 #include "json.h"
 #include "selftest.h"
@@ -43,21 +44,43 @@ static json::array *cur_children_array;
 /* Generate a JSON object for LOC.  */
 
 json::value *
-json_from_expanded_location (location_t loc)
+json_from_expanded_location (diagnostic_context *context, location_t loc)
 {
   expanded_location exploc = expand_location (loc);
   json::object *result = new json::object ();
   if (exploc.file)
     result->set ("file", new json::string (exploc.file));
   result->set ("line", new json::integer_number (exploc.line));
-  result->set ("column", new json::integer_number (exploc.column));
+
+  const enum diagnostics_column_unit orig_unit = context->column_unit;
+  struct
+  {
+    const char *name;
+    enum diagnostics_column_unit unit;
+  } column_fields[] = {
+    {"display-column", DIAGNOSTICS_COLUMN_UNIT_DISPLAY},
+    {"byte-column", DIAGNOSTICS_COLUMN_UNIT_BYTE}
+  };
+  int the_column = INT_MIN;
+  for (int i = 0; i != sizeof column_fields / sizeof (*column_fields); ++i)
+    {
+      context->column_unit = column_fields[i].unit;
+      const int col = diagnostic_converted_column (context, exploc);
+      result->set (column_fields[i].name, new json::integer_number (col));
+      if (column_fields[i].unit == orig_unit)
+	the_column = col;
+    }
+  gcc_assert (the_column != INT_MIN);
+  result->set ("column", new json::integer_number (the_column));
+  context->column_unit = orig_unit;
   return result;
 }
 
 /* Generate a JSON object for LOC_RANGE.  */
 
 static json::object *
-json_from_location_range (const location_range *loc_range, unsigned range_idx)
+json_from_location_range (diagnostic_context *context,
+			  const location_range *loc_range, unsigned range_idx)
 {
   location_t caret_loc = get_pure_location (loc_range->m_loc);
 
@@ -68,13 +91,13 @@ json_from_location_range (const location
   location_t finish_loc = get_finish (loc_range->m_loc);
 
   json::object *result = new json::object ();
-  result->set ("caret", json_from_expanded_location (caret_loc));
+  result->set ("caret", json_from_expanded_location (context, caret_loc));
   if (start_loc != caret_loc
       && start_loc != UNKNOWN_LOCATION)
-    result->set ("start", json_from_expanded_location (start_loc));
+    result->set ("start", json_from_expanded_location (context, start_loc));
   if (finish_loc != caret_loc
       && finish_loc != UNKNOWN_LOCATION)
-    result->set ("finish", json_from_expanded_location (finish_loc));
+    result->set ("finish", json_from_expanded_location (context, finish_loc));
 
   if (loc_range->m_label)
     {
@@ -91,14 +114,14 @@ json_from_location_range (const location
 /* Generate a JSON object for HINT.  */
 
 static json::object *
-json_from_fixit_hint (const fixit_hint *hint)
+json_from_fixit_hint (diagnostic_context *context, const fixit_hint *hint)
 {
   json::object *fixit_obj = new json::object ();
 
   location_t start_loc = hint->get_start_loc ();
-  fixit_obj->set ("start", json_from_expanded_location (start_loc));
+  fixit_obj->set ("start", json_from_expanded_location (context, start_loc));
   location_t next_loc = hint->get_next_loc ();
-  fixit_obj->set ("next", json_from_expanded_location (next_loc));
+  fixit_obj->set ("next", json_from_expanded_location (context, next_loc));
   fixit_obj->set ("string", new json::string (hint->get_string ()));
 
   return fixit_obj;
@@ -190,11 +213,13 @@ json_end_diagnostic (diagnostic_context
   else
     {
       /* Otherwise, make diag_obj be the top-level object within the group;
-	 add a "children" array.  */
+	 add a "children" array and record the column origin.  */
       toplevel_array->append (diag_obj);
       cur_group = diag_obj;
       cur_children_array = new json::array ();
       diag_obj->set ("children", cur_children_array);
+      diag_obj->set ("column-origin",
+		     new json::integer_number (context->column_origin));
     }
 
   const rich_location *richloc = diagnostic->richloc;
@@ -205,7 +230,7 @@ json_end_diagnostic (diagnostic_context
   for (unsigned int i = 0; i < richloc->get_num_locations (); i++)
     {
       const location_range *loc_range = richloc->get_range (i);
-      json::object *loc_obj = json_from_location_range (loc_range, i);
+      json::object *loc_obj = json_from_location_range (context, loc_range, i);
       if (loc_obj)
 	loc_array->append (loc_obj);
     }
@@ -217,7 +242,7 @@ json_end_diagnostic (diagnostic_context
       for (unsigned int i = 0; i < richloc->get_num_fixit_hints (); i++)
 	{
 	  const fixit_hint *hint = richloc->get_fixit_hint (i);
-	  json::object *fixit_obj = json_from_fixit_hint (hint);
+	  json::object *fixit_obj = json_from_fixit_hint (context, hint);
 	  fixit_array->append (fixit_obj);
 	}
     }
@@ -320,7 +345,8 @@ namespace selftest {
 static void
 test_unknown_location ()
 {
-  delete json_from_expanded_location (UNKNOWN_LOCATION);
+  test_diagnostic_context dc;
+  delete json_from_expanded_location (&dc, UNKNOWN_LOCATION);
 }
 
 /* Verify that we gracefully handle attempts to serialize bad
@@ -338,7 +364,8 @@ test_bad_endpoints ()
   loc_range.m_range_display_kind = SHOW_RANGE_WITH_CARET;
   loc_range.m_label = NULL;
 
-  json::object *obj = json_from_location_range (&loc_range, 0);
+  test_diagnostic_context dc;
+  json::object *obj = json_from_location_range (&dc, &loc_range, 0);
   /* We should have a "caret" value, but no "start" or "finish" values.  */
   ASSERT_TRUE (obj != NULL);
   ASSERT_TRUE (obj->get ("caret") != NULL);
diff --git a/gcc/diagnostic.h b/gcc/diagnostic.h
--- a/gcc/diagnostic.h	2020-07-22 23:35:17.556386887 -0700
+++ b/gcc/diagnostic.h	2021-12-25 01:20:53.479636627 -0800
@@ -24,6 +24,20 @@ along with GCC; see the file COPYING3.
 #include "pretty-print.h"
 #include "diagnostic-core.h"
 
+/* An enum for controlling what units to use for the column number
+   when diagnostics are output, used by the -fdiagnostics-column-unit option.
+   Tabs will be expanded or not according to the value of -ftabstop.  The origin
+   (default 1) is controlled by -fdiagnostics-column-origin.  */
+
+enum diagnostics_column_unit
+{
+  /* The default from GCC 11 onwards: display columns.  */
+  DIAGNOSTICS_COLUMN_UNIT_DISPLAY,
+
+  /* The behavior in GCC 10 and earlier: simple bytes.  */
+  DIAGNOSTICS_COLUMN_UNIT_BYTE
+};
+
 /* Enum for overriding the standard output format.  */
 
 enum diagnostics_output_format
@@ -280,6 +294,15 @@ struct diagnostic_context
      rest of the diagnostic.  */
   bool parseable_fixits_p;
 
+  /* What units to use when outputting the column number.  */
+  enum diagnostics_column_unit column_unit;
+
+  /* The origin for the column number (1-based or 0-based typically).  */
+  int column_origin;
+
+  /* The size of the tabstop for tab expansion.  */
+  int tabstop;
+
   /* If non-NULL, an edit_context to which fix-it hints should be
      applied, for generating patches.  */
   edit_context *edit_context_ptr;
@@ -458,6 +481,8 @@ diagnostic_same_line (const diagnostic_c
 }
 
 extern const char *diagnostic_get_color_for_kind (diagnostic_t kind);
+extern int diagnostic_converted_column (diagnostic_context *context,
+					expanded_location s);
 
 /* Pure text formatting support functions.  */
 extern char *file_name_as_prefix (diagnostic_context *, const char *);
@@ -470,6 +495,7 @@ extern void diagnostic_output_format_ini
 /* Compute the number of digits in the decimal representation of an integer.  */
 extern int num_digits (int);
 
-extern json::value *json_from_expanded_location (location_t loc);
+extern json::value *json_from_expanded_location (diagnostic_context *context,
+						 location_t loc);
 
 #endif /* ! GCC_DIAGNOSTIC_H */
diff --git a/gcc/diagnostic-show-locus.c b/gcc/diagnostic-show-locus.c
--- a/gcc/diagnostic-show-locus.c	2020-07-22 23:35:17.556386887 -0700
+++ b/gcc/diagnostic-show-locus.c	2021-12-25 01:20:53.479636627 -0800
@@ -175,9 +175,10 @@ enum column_unit {
 class exploc_with_display_col : public expanded_location
 {
  public:
-  exploc_with_display_col (const expanded_location &exploc)
+  exploc_with_display_col (const expanded_location &exploc, int tabstop)
     : expanded_location (exploc),
-      m_display_col (location_compute_display_column (exploc)) {}
+      m_display_col (location_compute_display_column (exploc, tabstop))
+  {}
 
   int m_display_col;
 };
@@ -189,11 +190,11 @@ class exploc_with_display_col : public e
 class layout_point
 {
  public:
-  layout_point (const expanded_location &exploc)
+  layout_point (const exploc_with_display_col &exploc)
     : m_line (exploc.line)
   {
     m_columns[CU_BYTES] = exploc.column;
-    m_columns[CU_DISPLAY_COLS] = location_compute_display_column (exploc);
+    m_columns[CU_DISPLAY_COLS] = exploc.m_display_col;
   }
 
   linenum_type m_line;
@@ -205,10 +206,10 @@ class layout_point
 class layout_range
 {
  public:
-  layout_range (const expanded_location *start_exploc,
-		const expanded_location *finish_exploc,
+  layout_range (const exploc_with_display_col &start_exploc,
+		const exploc_with_display_col &finish_exploc,
 		enum range_display_kind range_display_kind,
-		const expanded_location *caret_exploc,
+		const exploc_with_display_col &caret_exploc,
 		unsigned original_idx,
 		const range_label *label);
 
@@ -226,22 +227,18 @@ class layout_range
 
 /* A struct for use by layout::print_source_line for telling
    layout::print_annotation_line the extents of the source line that
-   it printed, so that underlines can be clipped appropriately.  */
+   it printed, so that underlines can be clipped appropriately.  Units
+   are 1-based display columns.  */
 
 struct line_bounds
 {
-  int m_first_non_ws;
-  int m_last_non_ws;
+  int m_first_non_ws_disp_col;
+  int m_last_non_ws_disp_col;
 
-  void convert_to_display_cols (char_span line)
+  line_bounds ()
   {
-    m_first_non_ws = cpp_byte_column_to_display_column (line.get_buffer (),
-							line.length (),
-							m_first_non_ws);
-
-    m_last_non_ws = cpp_byte_column_to_display_column (line.get_buffer (),
-						       line.length (),
-						       m_last_non_ws);
+    m_first_non_ws_disp_col = INT_MAX;
+    m_last_non_ws_disp_col = 0;
   }
 };
 
@@ -351,8 +348,8 @@ class layout
  private:
   bool will_show_line_p (linenum_type row) const;
   void print_leading_fixits (linenum_type row);
-  void print_source_line (linenum_type row, const char *line, int line_bytes,
-			  line_bounds *lbounds_out);
+  line_bounds print_source_line (linenum_type row, const char *line,
+				 int line_bytes);
   bool should_print_annotation_line_p (linenum_type row) const;
   void start_annotation_line (char margin_char = ' ') const;
   void print_annotation_line (linenum_type row, const line_bounds lbounds);
@@ -513,16 +510,16 @@ colorizer::get_color_by_name (const char
    Initialize various layout_point fields from expanded_location
    equivalents; we've already filtered on file.  */
 
-layout_range::layout_range (const expanded_location *start_exploc,
-			    const expanded_location *finish_exploc,
+layout_range::layout_range (const exploc_with_display_col &start_exploc,
+			    const exploc_with_display_col &finish_exploc,
 			    enum range_display_kind range_display_kind,
-			    const expanded_location *caret_exploc,
+			    const exploc_with_display_col &caret_exploc,
 			    unsigned original_idx,
 			    const range_label *label)
-: m_start (*start_exploc),
-  m_finish (*finish_exploc),
+: m_start (start_exploc),
+  m_finish (finish_exploc),
   m_range_display_kind (range_display_kind),
-  m_caret (*caret_exploc),
+  m_caret (caret_exploc),
   m_original_idx (original_idx),
   m_label (label)
 {
@@ -646,6 +643,9 @@ layout_range::intersects_line_p (linenum
 
 #if CHECKING_P
 
+/* Default for when we don't care what the tab expansion is set to.  */
+static const int def_tabstop = 8;
+
 /* Create some expanded locations for testing layout_range.  The filename
    member of the explocs is set to the empty string.  This member will only be
    inspected by the calls to location_compute_display_column() made from the
@@ -662,8 +662,11 @@ make_range (int start_line, int start_co
     = {"", start_line, start_col, NULL, false};
   const expanded_location finish_exploc
     = {"", end_line, end_col, NULL, false};
-  return layout_range (&start_exploc, &finish_exploc, SHOW_RANGE_WITHOUT_CARET,
-		       &start_exploc, 0, NULL);
+  return layout_range (exploc_with_display_col (start_exploc, def_tabstop),
+		       exploc_with_display_col (finish_exploc, def_tabstop),
+		       SHOW_RANGE_WITHOUT_CARET,
+		       exploc_with_display_col (start_exploc, def_tabstop),
+		       0, NULL);
 }
 
 /* Selftests for layout_range::contains_point and
@@ -964,7 +967,7 @@ layout::layout (diagnostic_context * con
 : m_context (context),
   m_pp (context->printer),
   m_primary_loc (richloc->get_range (0)->m_loc),
-  m_exploc (richloc->get_expanded_location (0)),
+  m_exploc (richloc->get_expanded_location (0), context->tabstop),
   m_colorizer (context, diagnostic_kind),
   m_colorize_source_p (context->colorize_source_p),
   m_show_labels_p (context->show_labels_p),
@@ -1060,7 +1063,10 @@ layout::maybe_add_location_range (const
 
   /* Everything is now known to be in the correct source file,
      but it may require further sanitization.  */
-  layout_range ri (&start, &finish, loc_range->m_range_display_kind, &caret,
+  layout_range ri (exploc_with_display_col (start, m_context->tabstop),
+		   exploc_with_display_col (finish, m_context->tabstop),
+		   loc_range->m_range_display_kind,
+		   exploc_with_display_col (caret, m_context->tabstop),
 		   original_idx, loc_range->m_label);
 
   /* If we have a range that finishes before it starts (perhaps
@@ -1394,7 +1400,7 @@ layout::calculate_x_offset_display ()
     = get_line_bytes_without_trailing_whitespace (line.get_buffer (),
 						  line.length ());
   int eol_display_column
-    = cpp_display_width (line.get_buffer (), line_bytes);
+    = cpp_display_width (line.get_buffer (), line_bytes, m_context->tabstop);
   if (caret_display_column > eol_display_column
       || !caret_display_column)
     {
@@ -1445,16 +1451,13 @@ layout::calculate_x_offset_display ()
 }
 
 /* Print line ROW of source code, potentially colorized at any ranges, and
-   populate *LBOUNDS_OUT.
-   LINE is the source line (not necessarily 0-terminated) and LINE_BYTES
-   is its length in bytes.
-   This function deals only with byte offsets, not display columns, so
-   m_x_offset_display must be converted from display to byte units.  In
-   particular, LINE_BYTES and LBOUNDS_OUT are in bytes.  */
+   return the line bounds.  LINE is the source line (not necessarily
+   0-terminated) and LINE_BYTES is its length in bytes.  In order to handle both
+   colorization and tab expansion, this function tracks the line position in
+   both byte and display column units.  */
 
-void
-layout::print_source_line (linenum_type row, const char *line, int line_bytes,
-			   line_bounds *lbounds_out)
+line_bounds
+layout::print_source_line (linenum_type row, const char *line, int line_bytes)
 {
   m_colorizer.set_normal_text ();
 
@@ -1469,30 +1472,29 @@ layout::print_source_line (linenum_type
   else
     pp_space (m_pp);
 
-  /* We will stop printing the source line at any trailing whitespace, and start
-     printing it as per m_x_offset_display.  */
+  /* We will stop printing the source line at any trailing whitespace.  */
   line_bytes = get_line_bytes_without_trailing_whitespace (line,
 							   line_bytes);
-  int x_offset_bytes = 0;
-  if (m_x_offset_display)
-    {
-      x_offset_bytes = cpp_display_column_to_byte_column (line, line_bytes,
-							  m_x_offset_display);
-      /* In case the leading portion of the line that will be skipped over ends
-	 with a character with wcwidth > 1, then it is possible we skipped too
-	 much, so account for that by padding with spaces.  */
-      const int overage
-	= cpp_byte_column_to_display_column (line, line_bytes, x_offset_bytes)
-	- m_x_offset_display;
-      for (int column = 0; column < overage; ++column)
-	pp_space (m_pp);
-      line += x_offset_bytes;
-    }
 
-  /* Print the line.  */
-  int first_non_ws = INT_MAX;
-  int last_non_ws = 0;
-  for (int col_byte = 1 + x_offset_bytes; col_byte <= line_bytes; col_byte++)
+  /* This object helps to keep track of which display column we are at, which is
+     necessary for computing the line bounds in display units, for doing
+     tab expansion, and for implementing m_x_offset_display.  */
+  cpp_display_width_computation dw (line, line_bytes, m_context->tabstop);
+
+  /* Skip the first m_x_offset_display display columns.  In case the leading
+     portion that will be skipped ends with a character with wcwidth > 1, then
+     it is possible we skipped too much, so account for that by padding with
+     spaces.  Note that this does the right thing too in case a tab was the last
+     character to be skipped over; the tab is effectively replaced by the
+     correct number of trailing spaces needed to offset by the desired number of
+     display columns.  */
+  for (int skipped_display_cols = dw.advance_display_cols (m_x_offset_display);
+       skipped_display_cols > m_x_offset_display; --skipped_display_cols)
+    pp_space (m_pp);
+
+  /* Print the line and compute the line_bounds.  */
+  line_bounds lbounds;
+  while (!dw.done ())
     {
       /* Assuming colorization is enabled for the caret and underline
 	 characters, we may also colorize the associated characters
@@ -1510,7 +1512,8 @@ layout::print_source_line (linenum_type
 	{
 	  bool in_range_p;
 	  point_state state;
-	  in_range_p = get_state_at_point (row, col_byte,
+	  const int start_byte_col = dw.bytes_processed () + 1;
+	  in_range_p = get_state_at_point (row, start_byte_col,
 					   0, INT_MAX,
 					   CU_BYTES,
 					   &state);
@@ -1519,22 +1522,44 @@ layout::print_source_line (linenum_type
 	  else
 	    m_colorizer.set_normal_text ();
 	}
-      char c = *line;
-      if (c == '\0' || c == '\t' || c == '\r')
-	c = ' ';
-      if (c != ' ')
+
+      /* Get the display width of the next character to be output, expanding
+	 tabs and replacing some control bytes with spaces as necessary.  */
+      const char *c = dw.next_byte ();
+      const int start_disp_col = dw.display_cols_processed () + 1;
+      const int this_display_width = dw.process_next_codepoint ();
+      if (*c == '\t')
+	{
+	  /* The returned display width is the number of spaces into which the
+	     tab should be expanded.  */
+	  for (int i = 0; i != this_display_width; ++i)
+	    pp_space (m_pp);
+	  continue;
+	}
+      if (*c == '\0' || *c == '\r')
 	{
-	  last_non_ws = col_byte;
-	  if (first_non_ws == INT_MAX)
-	    first_non_ws = col_byte;
+	  /* cpp_wcwidth() promises to return 1 for all control bytes, and we
+	     want to output these as a single space too, so this case is
+	     actually the same as the '\t' case.  */
+	  gcc_assert (this_display_width == 1);
+	  pp_space (m_pp);
+	  continue;
 	}
-      pp_character (m_pp, c);
-      line++;
+
+      /* We have a (possibly multibyte) character to output; update the line
+	 bounds if it is not whitespace.  */
+      if (*c != ' ')
+	{
+	  lbounds.m_last_non_ws_disp_col = dw.display_cols_processed ();
+	  if (lbounds.m_first_non_ws_disp_col == INT_MAX)
+	    lbounds.m_first_non_ws_disp_col = start_disp_col;
+	}
+
+      /* Output the character.  */
+      while (c != dw.next_byte ()) pp_character (m_pp, *c++);
     }
   print_newline ();
-
-  lbounds_out->m_first_non_ws = first_non_ws;
-  lbounds_out->m_last_non_ws = last_non_ws;
+  return lbounds;
 }
 
 /* Determine if we should print an annotation line for ROW.
@@ -1576,14 +1601,13 @@ layout::start_annotation_line (char marg
 }
 
 /* Print a line consisting of the caret/underlines for the given
-   source line.  This function works with display columns, rather than byte
-   counts; in particular, LBOUNDS should be in display column units.  */
+   source line.  */
 
 void
 layout::print_annotation_line (linenum_type row, const line_bounds lbounds)
 {
   int x_bound = get_x_bound_for_row (row, m_exploc.m_display_col,
-				     lbounds.m_last_non_ws);
+				     lbounds.m_last_non_ws_disp_col);
 
   start_annotation_line ();
   pp_space (m_pp);
@@ -1593,8 +1617,8 @@ layout::print_annotation_line (linenum_t
       bool in_range_p;
       point_state state;
       in_range_p = get_state_at_point (row, column,
-				       lbounds.m_first_non_ws,
-				       lbounds.m_last_non_ws,
+				       lbounds.m_first_non_ws_disp_col,
+				       lbounds.m_last_non_ws_disp_col,
 				       CU_DISPLAY_COLS,
 				       &state);
       if (in_range_p)
@@ -1631,12 +1655,14 @@ layout::print_annotation_line (linenum_t
 class line_label
 {
 public:
-  line_label (int state_idx, int column, label_text text)
+  line_label (diagnostic_context *context, int state_idx, int column,
+	      label_text text)
   : m_state_idx (state_idx), m_column (column),
     m_text (text), m_label_line (0), m_has_vbar (true)
   {
     const int bytes = strlen (text.m_buffer);
-    m_display_width = cpp_display_width (text.m_buffer, bytes);
+    m_display_width
+      = cpp_display_width (text.m_buffer, bytes, context->tabstop);
   }
 
   /* Sorting is primarily by column, then by state index.  */
@@ -1696,7 +1722,7 @@ layout::print_any_labels (linenum_type r
 	if (text.m_buffer == NULL)
 	  continue;
 
-	labels.safe_push (line_label (i, disp_col, text));
+	labels.safe_push (line_label (m_context, i, disp_col, text));
       }
   }
 
@@ -1976,7 +2002,8 @@ public:
 
 /* Get the range of bytes or display columns that HINT would affect.  */
 static column_range
-get_affected_range (const fixit_hint *hint, enum column_unit col_unit)
+get_affected_range (diagnostic_context *context,
+		    const fixit_hint *hint, enum column_unit col_unit)
 {
   expanded_location exploc_start = expand_location (hint->get_start_loc ());
   expanded_location exploc_finish = expand_location (hint->get_next_loc ());
@@ -1986,11 +2013,13 @@ get_affected_range (const fixit_hint *hi
   int finish_column;
   if (col_unit == CU_DISPLAY_COLS)
     {
-      start_column = location_compute_display_column (exploc_start);
+      start_column
+	= location_compute_display_column (exploc_start, context->tabstop);
       if (hint->insertion_p ())
 	finish_column = start_column - 1;
       else
-	finish_column = location_compute_display_column (exploc_finish);
+	finish_column
+	  = location_compute_display_column (exploc_finish, context->tabstop);
     }
   else
     {
@@ -2003,12 +2032,12 @@ get_affected_range (const fixit_hint *hi
 /* Get the range of display columns that would be printed for HINT.  */
 
 static column_range
-get_printed_columns (const fixit_hint *hint)
+get_printed_columns (diagnostic_context *context, const fixit_hint *hint)
 {
   expanded_location exploc = expand_location (hint->get_start_loc ());
-  int start_column = location_compute_display_column (exploc);
-  int hint_width = cpp_display_width (hint->get_string (),
-				      hint->get_length ());
+  int start_column = location_compute_display_column (exploc, context->tabstop);
+  int hint_width = cpp_display_width (hint->get_string (), hint->get_length (),
+				      context->tabstop);
   int final_hint_column = start_column + hint_width - 1;
   if (hint->insertion_p ())
     {
@@ -2018,7 +2047,8 @@ get_printed_columns (const fixit_hint *h
     {
       exploc = expand_location (hint->get_next_loc ());
       --exploc.column;
-      int finish_column = location_compute_display_column (exploc);
+      int finish_column
+	= location_compute_display_column (exploc, context->tabstop);
       return column_range (start_column,
 			   MAX (finish_column, final_hint_column));
     }
@@ -2035,12 +2065,14 @@ public:
   correction (column_range affected_bytes,
 	      column_range affected_columns,
 	      column_range printed_columns,
-	      const char *new_text, size_t new_text_len)
+	      const char *new_text, size_t new_text_len,
+	      int tabstop)
   : m_affected_bytes (affected_bytes),
     m_affected_columns (affected_columns),
     m_printed_columns (printed_columns),
     m_text (xstrdup (new_text)),
     m_byte_length (new_text_len),
+    m_tabstop (tabstop),
     m_alloc_sz (new_text_len + 1)
   {
     compute_display_cols ();
@@ -2058,7 +2090,7 @@ public:
 
   void compute_display_cols ()
   {
-    m_display_cols = cpp_display_width (m_text, m_byte_length);
+    m_display_cols = cpp_display_width (m_text, m_byte_length, m_tabstop);
   }
 
   void overwrite (int dst_offset, const char_span &src_span)
@@ -2086,6 +2118,7 @@ public:
   char *m_text;
   size_t m_byte_length; /* Not including null-terminator.  */
   int m_display_cols;
+  int m_tabstop;
   size_t m_alloc_sz;
 };
 
@@ -2121,13 +2154,15 @@ correction::ensure_terminated ()
 class line_corrections
 {
 public:
-  line_corrections (const char *filename, linenum_type row)
-  : m_filename (filename), m_row (row)
+  line_corrections (diagnostic_context *context, const char *filename,
+		    linenum_type row)
+    : m_context (context), m_filename (filename), m_row (row)
   {}
   ~line_corrections ();
 
   void add_hint (const fixit_hint *hint);
 
+  diagnostic_context *m_context;
   const char *m_filename;
   linenum_type m_row;
   auto_vec <correction *> m_corrections;
@@ -2173,9 +2208,10 @@ source_line::source_line (const char *fi
 void
 line_corrections::add_hint (const fixit_hint *hint)
 {
-  column_range affected_bytes = get_affected_range (hint, CU_BYTES);
-  column_range affected_columns = get_affected_range (hint, CU_DISPLAY_COLS);
-  column_range printed_columns = get_printed_columns (hint);
+  column_range affected_bytes = get_affected_range (m_context, hint, CU_BYTES);
+  column_range affected_columns = get_affected_range (m_context, hint,
+						      CU_DISPLAY_COLS);
+  column_range printed_columns = get_printed_columns (m_context, hint);
 
   /* Potentially consolidate.  */
   if (!m_corrections.is_empty ())
@@ -2243,7 +2279,8 @@ line_corrections::add_hint (const fixit_
 					   affected_columns,
 					   printed_columns,
 					   hint->get_string (),
-					   hint->get_length ()));
+					   hint->get_length (),
+					   m_context->tabstop));
 }
 
 /* If there are any fixit hints on source line ROW, print them.
@@ -2257,7 +2294,7 @@ layout::print_trailing_fixits (linenum_t
 {
   /* Build a list of correction instances for the line,
      potentially consolidating hints (for the sake of readability).  */
-  line_corrections corrections (m_exploc.file, row);
+  line_corrections corrections (m_context, m_exploc.file, row);
   for (unsigned int i = 0; i < m_fixit_hints.length (); i++)
     {
       const fixit_hint *hint = m_fixit_hints[i];
@@ -2499,15 +2536,11 @@ layout::print_line (linenum_type row)
   if (!line)
     return;
 
-  line_bounds lbounds;
   print_leading_fixits (row);
-  print_source_line (row, line.get_buffer (), line.length (), &lbounds);
+  const line_bounds lbounds
+    = print_source_line (row, line.get_buffer (), line.length ());
   if (should_print_annotation_line_p (row))
-    {
-      if (lbounds.m_first_non_ws != INT_MAX)
-	lbounds.convert_to_display_cols (line);
-      print_annotation_line (row, lbounds);
-    }
+    print_annotation_line (row, lbounds);
   if (m_show_labels_p)
     print_any_labels (row);
   print_trailing_fixits (row);
@@ -2670,9 +2703,11 @@ test_layout_x_offset_display_utf8 (const
 
   char_span lspan = location_get_source_line (tmp.get_filename (), 1);
   ASSERT_EQ (line_display_cols,
-	     cpp_display_width (lspan.get_buffer (), lspan.length ()));
+	     cpp_display_width (lspan.get_buffer (), lspan.length (),
+				def_tabstop));
   ASSERT_EQ (line_display_cols,
-	     location_compute_display_column (expand_location (line_end)));
+	     location_compute_display_column (expand_location (line_end),
+					      def_tabstop));
   ASSERT_EQ (0, memcmp (lspan.get_buffer () + (emoji_col - 1),
 			"\xf0\x9f\x98\x82\xf0\x9f\x98\x82", 8));
 
@@ -2774,6 +2809,111 @@ test_layout_x_offset_display_utf8 (const
 
 }
 
+static void
+test_layout_x_offset_display_tab (const line_table_case &case_)
+{
+  const char *content
+    = "This line is very long, so that we can use it to test the logic for "
+      "clipping long lines.  Also this: `\t' is a tab that occupies 1 byte and "
+      "a variable number of display columns, starting at column #103.\n";
+
+  /* Number of bytes in the line, subtracting one to remove the newline.  */
+  const int line_bytes = strlen (content) - 1;
+
+ /* The column where the tab begins.  Byte or display is the same as there are
+    no multibyte characters earlier on the line.  */
+  const int tab_col = 103;
+
+  /* Effective extra size of the tab beyond what a single space would have taken
+     up, indexed by tabstop.  */
+  static const int num_tabstops = 11;
+  int extra_width[num_tabstops];
+  for (int tabstop = 1; tabstop != num_tabstops; ++tabstop)
+    {
+      const int this_tab_size = tabstop - (tab_col - 1) % tabstop;
+      extra_width[tabstop] = this_tab_size - 1;
+    }
+  /* Example of this calculation: if tabstop is 10, the tab starting at column
+     #103 has to expand into 8 spaces, covering columns 103-110, so that the
+     next character is at column #111.  So it takes up 7 more columns than
+     a space would have taken up.  */
+  ASSERT_EQ (7, extra_width[10]);
+
+  temp_source_file tmp (SELFTEST_LOCATION, ".c", content);
+  line_table_test ltt (case_);
+
+  linemap_add (line_table, LC_ENTER, false, tmp.get_filename (), 1);
+
+  location_t line_end = linemap_position_for_column (line_table, line_bytes);
+
+  /* Don't attempt to run the tests if column data might be unavailable.  */
+  if (line_end > LINE_MAP_MAX_LOCATION_WITH_COLS)
+    return;
+
+  /* Check that cpp_display_width handles the tabs as expected.  */
+  char_span lspan = location_get_source_line (tmp.get_filename (), 1);
+  ASSERT_EQ ('\t', *(lspan.get_buffer () + (tab_col - 1)));
+  for (int tabstop = 1; tabstop != num_tabstops; ++tabstop)
+    {
+      ASSERT_EQ (line_bytes + extra_width[tabstop],
+		 cpp_display_width (lspan.get_buffer (), lspan.length (),
+				    tabstop));
+      ASSERT_EQ (line_bytes + extra_width[tabstop],
+		 location_compute_display_column (expand_location (line_end),
+						  tabstop));
+    }
+
+  /* Check that the tab is expanded to the expected number of spaces.  */
+  rich_location richloc (line_table,
+			 linemap_position_for_column (line_table,
+						      tab_col + 1));
+  for (int tabstop = 1; tabstop != num_tabstops; ++tabstop)
+    {
+      test_diagnostic_context dc;
+      dc.tabstop = tabstop;
+      layout test_layout (&dc, &richloc, DK_ERROR);
+      test_layout.print_line (1);
+      const char *out = pp_formatted_text (dc.printer);
+      ASSERT_EQ (NULL, strchr (out, '\t'));
+      const char *left_quote = strchr (out, '`');
+      const char *right_quote = strchr (out, '\'');
+      ASSERT_NE (NULL, left_quote);
+      ASSERT_NE (NULL, right_quote);
+      ASSERT_EQ (right_quote - left_quote, extra_width[tabstop] + 2);
+    }
+
+  /* Check that the line is offset properly and that the tab is broken up
+     into the expected number of spaces when it is the last character skipped
+     over.  */
+  for (int tabstop = 1; tabstop != num_tabstops; ++tabstop)
+    {
+      test_diagnostic_context dc;
+      dc.tabstop = tabstop;
+      static const int small_width = 24;
+      dc.caret_max_width = small_width - 4;
+      dc.min_margin_width = test_left_margin - test_linenum_sep + 1;
+      dc.show_line_numbers_p = true;
+      layout test_layout (&dc, &richloc, DK_ERROR);
+      test_layout.print_line (1);
+
+      /* We have arranged things so that two columns will be printed before
+	 the caret.  If the tab results in more than one space, this should
+	 produce two spaces in the output; otherwise, it will be a single space
+	 preceded by the opening quote before the tab character.  */
+      const char *output1
+	= "   1 |   ' is a tab that occupies 1 byte and a variable number of "
+	  "display columns, starting at column #103.\n"
+	  "     |   ^\n\n";
+      const char *output2
+	= "   1 | ` ' is a tab that occupies 1 byte and a variable number of "
+	  "display columns, starting at column #103.\n"
+	  "     |   ^\n\n";
+      const char *expected_output = (extra_width[tabstop] ? output1 : output2);
+      ASSERT_STREQ (expected_output, pp_formatted_text (dc.printer));
+    }
+}
+
+
 /* Verify that diagnostic_show_locus works sanely on UNKNOWN_LOCATION.  */
 
 static void
@@ -3854,6 +3994,27 @@ test_one_liner_labels_utf8 ()
   }
 }
 
+/* Make sure that colorization codes don't interrupt a multibyte
+   sequence, which would corrupt it.  */
+static void
+test_one_liner_colorized_utf8 ()
+{
+  test_diagnostic_context dc;
+  dc.colorize_source_p = true;
+  diagnostic_color_init (&dc, DIAGNOSTICS_COLOR_YES);
+  const location_t pi = linemap_position_for_column (line_table, 12);
+  rich_location richloc (line_table, pi);
+  diagnostic_show_locus (&dc, &richloc, DK_ERROR);
+
+  /* In order to avoid having the test depend on exactly how the colorization
+     was effected, just confirm there are two pi characters in the output.  */
+  const char *result = pp_formatted_text (dc.printer);
+  const char *null_term = result + strlen (result);
+  const char *first_pi = strstr (result, "\xcf\x80");
+  ASSERT_TRUE (first_pi && first_pi <= null_term - 2);
+  ASSERT_STR_CONTAINS (first_pi + 2, "\xcf\x80");
+}
+
 /* Run the various one-liner tests.  */
 
 static void
@@ -3884,8 +4045,10 @@ test_diagnostic_show_locus_one_liner_utf
   ASSERT_EQ (31, LOCATION_COLUMN (line_end));
 
   char_span lspan = location_get_source_line (tmp.get_filename (), 1);
-  ASSERT_EQ (25, cpp_display_width (lspan.get_buffer (), lspan.length ()));
-  ASSERT_EQ (25, location_compute_display_column (expand_location (line_end)));
+  ASSERT_EQ (25, cpp_display_width (lspan.get_buffer (), lspan.length (),
+				    def_tabstop));
+  ASSERT_EQ (25, location_compute_display_column (expand_location (line_end),
+						  def_tabstop));
 
   test_one_liner_simple_caret_utf8 ();
   test_one_liner_caret_and_range_utf8 ();
@@ -3900,6 +4063,7 @@ test_diagnostic_show_locus_one_liner_utf
   test_one_liner_many_fixits_1_utf8 ();
   test_one_liner_many_fixits_2_utf8 ();
   test_one_liner_labels_utf8 ();
+  test_one_liner_colorized_utf8 ();
 }
 
 /* Verify that gcc_rich_location::add_location_if_nearby works.  */
@@ -4272,25 +4436,28 @@ test_overlapped_fixit_printing (const li
     /* Unit-test the line_corrections machinery.  */
     ASSERT_EQ (3, richloc.get_num_fixit_hints ());
     const fixit_hint *hint_0 = richloc.get_fixit_hint (0);
-    ASSERT_EQ (column_range (12, 12), get_affected_range (hint_0, CU_BYTES));
     ASSERT_EQ (column_range (12, 12),
-			   get_affected_range (hint_0, CU_DISPLAY_COLS));
-    ASSERT_EQ (column_range (12, 22), get_printed_columns (hint_0));
+	       get_affected_range (&dc, hint_0, CU_BYTES));
+    ASSERT_EQ (column_range (12, 12),
+	       get_affected_range (&dc, hint_0, CU_DISPLAY_COLS));
+    ASSERT_EQ (column_range (12, 22), get_printed_columns (&dc, hint_0));
     const fixit_hint *hint_1 = richloc.get_fixit_hint (1);
-    ASSERT_EQ (column_range (18, 18), get_affected_range (hint_1, CU_BYTES));
     ASSERT_EQ (column_range (18, 18),
-			   get_affected_range (hint_1, CU_DISPLAY_COLS));
-    ASSERT_EQ (column_range (18, 20), get_printed_columns (hint_1));
+	       get_affected_range (&dc, hint_1, CU_BYTES));
+    ASSERT_EQ (column_range (18, 18),
+	       get_affected_range (&dc, hint_1, CU_DISPLAY_COLS));
+    ASSERT_EQ (column_range (18, 20), get_printed_columns (&dc, hint_1));
     const fixit_hint *hint_2 = richloc.get_fixit_hint (2);
-    ASSERT_EQ (column_range (29, 28), get_affected_range (hint_2, CU_BYTES));
     ASSERT_EQ (column_range (29, 28),
-			   get_affected_range (hint_2, CU_DISPLAY_COLS));
-    ASSERT_EQ (column_range (29, 29), get_printed_columns (hint_2));
+	       get_affected_range (&dc, hint_2, CU_BYTES));
+    ASSERT_EQ (column_range (29, 28),
+	       get_affected_range (&dc, hint_2, CU_DISPLAY_COLS));
+    ASSERT_EQ (column_range (29, 29), get_printed_columns (&dc, hint_2));
 
     /* Add each hint in turn to a line_corrections instance,
        and verify that they are consolidated into one correction instance
        as expected.  */
-    line_corrections lc (tmp.get_filename (), 1);
+    line_corrections lc (&dc, tmp.get_filename (), 1);
 
     /* The first replace hint by itself.  */
     lc.add_hint (hint_0);
@@ -4484,25 +4651,28 @@ test_overlapped_fixit_printing_utf8 (con
     /* Unit-test the line_corrections machinery.  */
     ASSERT_EQ (3, richloc.get_num_fixit_hints ());
     const fixit_hint *hint_0 = richloc.get_fixit_hint (0);
-    ASSERT_EQ (column_range (14, 14), get_affected_range (hint_0, CU_BYTES));
+    ASSERT_EQ (column_range (14, 14),
+	       get_affected_range (&dc, hint_0, CU_BYTES));
     ASSERT_EQ (column_range (12, 12),
-			   get_affected_range (hint_0, CU_DISPLAY_COLS));
-    ASSERT_EQ (column_range (12, 22), get_printed_columns (hint_0));
+	       get_affected_range (&dc, hint_0, CU_DISPLAY_COLS));
+    ASSERT_EQ (column_range (12, 22), get_printed_columns (&dc, hint_0));
     const fixit_hint *hint_1 = richloc.get_fixit_hint (1);
-    ASSERT_EQ (column_range (22, 22), get_affected_range (hint_1, CU_BYTES));
+    ASSERT_EQ (column_range (22, 22),
+	       get_affected_range (&dc, hint_1, CU_BYTES));
     ASSERT_EQ (column_range (18, 18),
-			   get_affected_range (hint_1, CU_DISPLAY_COLS));
-    ASSERT_EQ (column_range (18, 20), get_printed_columns (hint_1));
+	       get_affected_range (&dc, hint_1, CU_DISPLAY_COLS));
+    ASSERT_EQ (column_range (18, 20), get_printed_columns (&dc, hint_1));
     const fixit_hint *hint_2 = richloc.get_fixit_hint (2);
-    ASSERT_EQ (column_range (35, 34), get_affected_range (hint_2, CU_BYTES));
+    ASSERT_EQ (column_range (35, 34),
+	       get_affected_range (&dc, hint_2, CU_BYTES));
     ASSERT_EQ (column_range (30, 29),
-			   get_affected_range (hint_2, CU_DISPLAY_COLS));
-    ASSERT_EQ (column_range (30, 30), get_printed_columns (hint_2));
+	       get_affected_range (&dc, hint_2, CU_DISPLAY_COLS));
+    ASSERT_EQ (column_range (30, 30), get_printed_columns (&dc, hint_2));
 
     /* Add each hint in turn to a line_corrections instance,
        and verify that they are consolidated into one correction instance
        as expected.  */
-    line_corrections lc (tmp.get_filename (), 1);
+    line_corrections lc (&dc, tmp.get_filename (), 1);
 
     /* The first replace hint by itself.  */
     lc.add_hint (hint_0);
@@ -4689,6 +4859,8 @@ test_overlapped_fixit_printing_2 (const
 
   /* Two insertions, in the wrong order.  */
   {
+    test_diagnostic_context dc;
+
     rich_location richloc (line_table, col_20);
     richloc.add_fixit_insert_before (col_23, "{");
     richloc.add_fixit_insert_before (col_21, "}");
@@ -4696,14 +4868,15 @@ test_overlapped_fixit_printing_2 (const
     /* These fixits should be accepted; they can't be consolidated.  */
     ASSERT_EQ (2, richloc.get_num_fixit_hints ());
     const fixit_hint *hint_0 = richloc.get_fixit_hint (0);
-    ASSERT_EQ (column_range (23, 22), get_affected_range (hint_0, CU_BYTES));
-    ASSERT_EQ (column_range (23, 23), get_printed_columns (hint_0));
+    ASSERT_EQ (column_range (23, 22),
+	       get_affected_range (&dc, hint_0, CU_BYTES));
+    ASSERT_EQ (column_range (23, 23), get_printed_columns (&dc, hint_0));
     const fixit_hint *hint_1 = richloc.get_fixit_hint (1);
-    ASSERT_EQ (column_range (21, 20), get_affected_range (hint_1, CU_BYTES));
-    ASSERT_EQ (column_range (21, 21), get_printed_columns (hint_1));
+    ASSERT_EQ (column_range (21, 20),
+	       get_affected_range (&dc, hint_1, CU_BYTES));
+    ASSERT_EQ (column_range (21, 21), get_printed_columns (&dc, hint_1));
 
     /* Verify that they're printed correctly.  */
-    test_diagnostic_context dc;
     diagnostic_show_locus (&dc, &richloc, DK_ERROR);
     ASSERT_STREQ (" int a5[][0][0] = { 1, 2 };\n"
 		  "                    ^\n"
@@ -4955,6 +5128,65 @@ test_fixit_deletion_affecting_newline (c
 		pp_formatted_text (dc.printer));
 }
 
+static void
+test_tab_expansion (const line_table_case &case_)
+{
+  /* Create a tempfile and write some text to it.  This example uses a tabstop
+     of 8, as the column numbers attempt to indicate:
+
+    .....................000.01111111111.22222333333  display
+    .....................123.90123456789.56789012345  columns  */
+  const char *content = "  \t   This: `\t' is a tab.\n";
+  /* ....................000 00000011111 11111222222  byte
+     ....................123 45678901234 56789012345  columns  */
+
+  const int tabstop = 8;
+  const int first_non_ws_byte_col = 7;
+  const int right_quote_byte_col = 15;
+  const int last_byte_col = 25;
+  ASSERT_EQ (35, cpp_display_width (content, last_byte_col, tabstop));
+
+  temp_source_file tmp (SELFTEST_LOCATION, ".c", content);
+  line_table_test ltt (case_);
+  linemap_add (line_table, LC_ENTER, false, tmp.get_filename (), 1);
+
+  /* Don't attempt to run the tests if column data might be unavailable.  */
+  location_t line_end = linemap_position_for_column (line_table, last_byte_col);
+  if (line_end > LINE_MAP_MAX_LOCATION_WITH_COLS)
+    return;
+
+  /* Check that the leading whitespace with mixed tabs and spaces is expanded
+     into 11 spaces.  Recall that print_line() also puts one space before
+     everything too.  */
+  {
+    test_diagnostic_context dc;
+    dc.tabstop = tabstop;
+    rich_location richloc (line_table,
+			   linemap_position_for_column (line_table,
+							first_non_ws_byte_col));
+    layout test_layout (&dc, &richloc, DK_ERROR);
+    test_layout.print_line (1);
+    ASSERT_STREQ ("            This: `      ' is a tab.\n"
+		  "            ^\n",
+		  pp_formatted_text (dc.printer));
+  }
+
+  /* Confirm the display width was tracked correctly across the internal tab
+     as well.  */
+  {
+    test_diagnostic_context dc;
+    dc.tabstop = tabstop;
+    rich_location richloc (line_table,
+			   linemap_position_for_column (line_table,
+							right_quote_byte_col));
+    layout test_layout (&dc, &richloc, DK_ERROR);
+    test_layout.print_line (1);
+    ASSERT_STREQ ("            This: `      ' is a tab.\n"
+		  "                         ^\n",
+		  pp_formatted_text (dc.printer));
+  }
+}
+
 /* Verify that line numbers are correctly printed for the case of
    a multiline range in which the width of the line numbers changes
    (e.g. from "9" to "10").  */
@@ -5012,6 +5244,7 @@ diagnostic_show_locus_c_tests ()
   test_layout_range_for_multiple_lines ();
 
   for_each_line_table_case (test_layout_x_offset_display_utf8);
+  for_each_line_table_case (test_layout_x_offset_display_tab);
 
   test_get_line_bytes_without_trailing_whitespace ();
 
@@ -5029,6 +5262,7 @@ diagnostic_show_locus_c_tests ()
   for_each_line_table_case (test_fixit_insert_containing_newline_2);
   for_each_line_table_case (test_fixit_replace_containing_newline);
   for_each_line_table_case (test_fixit_deletion_affecting_newline);
+  for_each_line_table_case (test_tab_expansion);
 
   test_line_numbers_multiline_range ();
 }
diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
--- a/gcc/doc/invoke.texi	2021-12-24 20:23:46.876739587 -0800
+++ b/gcc/doc/invoke.texi	2021-12-25 01:20:53.487636494 -0800
@@ -293,7 +293,9 @@ Objective-C and Objective-C++ Dialects}.
 -fdiagnostics-show-template-tree  -fno-elide-type @gol
 -fdiagnostics-path-format=@r{[}none@r{|}separate-events@r{|}inline-events@r{]} @gol
 -fdiagnostics-show-path-depths @gol
--fno-show-column}
+-fno-show-column @gol
+-fdiagnostics-column-unit=@r{[}display@r{|}byte@r{]} @gol
+-fdiagnostics-column-origin=@var{origin}}
 
 @item Warning Options
 @xref{Warning Options,,Options to Request or Suppress Warnings}.
@@ -4424,6 +4426,31 @@ Do not print column numbers in diagnosti
 diagnostics are being scanned by a program that does not understand the
 column numbers, such as @command{dejagnu}.
 
+@item -fdiagnostics-column-unit=@var{UNIT}
+@opindex fdiagnostics-column-unit
+Select the units for the column number.  This affects traditional diagnostics
+(in the absence of @option{-fno-show-column}), as well as JSON format
+diagnostics if requested.
+
+The default @var{UNIT}, @samp{display}, considers the number of display
+columns occupied by each character.  This may be larger than the number
+of bytes required to encode the character, in the case of tab
+characters, or it may be smaller, in the case of multibyte characters.
+For example, the character ``GREEK SMALL LETTER PI (U+03C0)'' occupies one
+display column, and its UTF-8 encoding requires two bytes; the character
+``SLIGHTLY SMILING FACE (U+1F642)'' occupies two display columns, and
+its UTF-8 encoding requires four bytes.
+
+Setting @var{UNIT} to @samp{byte} changes the column number to the raw byte
+count in all cases, as was traditionally output by GCC prior to version 11.1.0.
+
+@item -fdiagnostics-column-origin=@var{ORIGIN}
+@opindex fdiagnostics-column-origin
+Select the origin for column numbers, i.e. the column number assigned to the
+first column.  The default value of 1 corresponds to traditional GCC
+behavior and to the GNU style guide.  Some utilities may perform better with an
+origin of 0; any non-negative value may be specified.
+
 @item -fdiagnostics-format=@var{FORMAT}
 @opindex fdiagnostics-format
 Select a different format for printing diagnostics.
@@ -4459,11 +4486,15 @@ might be printed in JSON form (after for
         "locations": [
             @{
                 "caret": @{
+		    "display-column": 3,
+		    "byte-column": 3,
                     "column": 3,
                     "file": "misleading-indentation.c",
                     "line": 15
                 @},
                 "finish": @{
+		    "display-column": 4,
+		    "byte-column": 4,
                     "column": 4,
                     "file": "misleading-indentation.c",
                     "line": 15
@@ -4479,6 +4510,8 @@ might be printed in JSON form (after for
                 "locations": [
                     @{
                         "caret": @{
+			    "display-column": 5,
+			    "byte-column": 5,
                             "column": 5,
                             "file": "misleading-indentation.c",
                             "line": 17
@@ -4488,6 +4521,7 @@ might be printed in JSON form (after for
                 "message": "...this statement, but the latter is @dots{}"
             @}
         ]
+	"column-origin": 1,
     @},
     @dots{}
 ]
@@ -4500,10 +4534,34 @@ A diagnostic has a @code{kind}.  If this
 an @code{option} key describing the command-line option controlling the
 warning.
 
-A diagnostic can contain zero or more locations.  Each location has up
-to three positions within it: a @code{caret} position and optional
-@code{start} and @code{finish} positions.  A location can also have
-an optional @code{label} string.  For example, this error:
+A diagnostic can contain zero or more locations.  Each location has an
+optional @code{label} string and up to three positions within it: a
+@code{caret} position and optional @code{start} and @code{finish} positions.
+A position is described by a @code{file} name, a @code{line} number, and
+three numbers indicating a column position:
+@itemize @bullet
+
+@item
+@code{display-column} counts display columns, accounting for tabs and
+multibyte characters.
+
+@item
+@code{byte-column} counts raw bytes.
+
+@item
+@code{column} is equal to one of
+the previous two, as dictated by the @option{-fdiagnostics-column-unit}
+option.
+
+@end itemize
+All three columns are relative to the origin specified by
+@option{-fdiagnostics-column-origin}, which is typically equal to 1 but may
+be set, for instance, to 0 for compatibility with other utilities that
+number columns from 0.  The column origin is recorded in the JSON output in
+the @code{column-origin} tag.  In the remaining examples below, the extra
+column number outputs have been omitted for brevity.
+
+For example, this error:
 
 @smallexample
 bad-binary-ops.c:64:23: error: invalid operands to binary + (have 'S' @{aka
diff --git a/gcc/input.c b/gcc/input.c
--- a/gcc/input.c	2020-07-22 23:35:17.664388078 -0700
+++ b/gcc/input.c	2021-12-25 01:20:53.487636494 -0800
@@ -913,7 +913,7 @@ make_location (location_t caret, source_
    source line in order to calculate the display width.  If that cannot be done
    for any reason, then returns the byte column as a fallback.  */
 int
-location_compute_display_column (expanded_location exploc)
+location_compute_display_column (expanded_location exploc, int tabstop)
 {
   if (!(exploc.file && *exploc.file && exploc.line && exploc.column))
     return exploc.column;
@@ -921,7 +921,7 @@ location_compute_display_column (expande
   /* If line is NULL, this function returns exploc.column which is the
      desired fallback.  */
   return cpp_byte_column_to_display_column (line.get_buffer (), line.length (),
-					    exploc.column);
+					    exploc.column, tabstop);
 }
 
 /* Dump statistics to stderr about the memory usage of the line_table
@@ -3608,33 +3608,46 @@ test_line_offset_overflow ()
 
 void test_cpp_utf8 ()
 {
+  const int def_tabstop = 8;
   /* Verify that wcwidth of invalid UTF-8 or control bytes is 1.  */
   {
-    int w_bad = cpp_display_width ("\xf0!\x9f!\x98!\x82!", 8);
+    int w_bad = cpp_display_width ("\xf0!\x9f!\x98!\x82!", 8, def_tabstop);
     ASSERT_EQ (8, w_bad);
-    int w_ctrl = cpp_display_width ("\r\t\n\v\0\1", 6);
-    ASSERT_EQ (6, w_ctrl);
+    int w_ctrl = cpp_display_width ("\r\n\v\0\1", 5, def_tabstop);
+    ASSERT_EQ (5, w_ctrl);
   }
 
   /* Verify that wcwidth of valid UTF-8 is as expected.  */
   {
-    const int w_pi = cpp_display_width ("\xcf\x80", 2);
+    const int w_pi = cpp_display_width ("\xcf\x80", 2, def_tabstop);
     ASSERT_EQ (1, w_pi);
-    const int w_emoji = cpp_display_width ("\xf0\x9f\x98\x82", 4);
+    const int w_emoji = cpp_display_width ("\xf0\x9f\x98\x82", 4, def_tabstop);
     ASSERT_EQ (2, w_emoji);
-    const int w_umlaut_precomposed = cpp_display_width ("\xc3\xbf", 2);
+    const int w_umlaut_precomposed = cpp_display_width ("\xc3\xbf", 2,
+							def_tabstop);
     ASSERT_EQ (1, w_umlaut_precomposed);
-    const int w_umlaut_combining = cpp_display_width ("y\xcc\x88", 3);
+    const int w_umlaut_combining = cpp_display_width ("y\xcc\x88", 3,
+						      def_tabstop);
     ASSERT_EQ (1, w_umlaut_combining);
-    const int w_han = cpp_display_width ("\xe4\xb8\xba", 3);
+    const int w_han = cpp_display_width ("\xe4\xb8\xba", 3, def_tabstop);
     ASSERT_EQ (2, w_han);
-    const int w_ascii = cpp_display_width ("GCC", 3);
+    const int w_ascii = cpp_display_width ("GCC", 3, def_tabstop);
     ASSERT_EQ (3, w_ascii);
     const int w_mixed = cpp_display_width ("\xcf\x80 = 3.14 \xf0\x9f\x98\x82"
-					   "\x9f! \xe4\xb8\xba y\xcc\x88", 24);
+					   "\x9f! \xe4\xb8\xba y\xcc\x88",
+					   24, def_tabstop);
     ASSERT_EQ (18, w_mixed);
   }
 
+  /* Verify that display width properly expands tabs.  */
+  {
+    const char *tstr = "\tabc\td";
+    ASSERT_EQ (6, cpp_display_width (tstr, 6, 1));
+    ASSERT_EQ (10, cpp_display_width (tstr, 6, 3));
+    ASSERT_EQ (17, cpp_display_width (tstr, 6, 8));
+    ASSERT_EQ (1, cpp_display_column_to_byte_column (tstr, 6, 7, 8));
+  }
+
   /* Verify that cpp_byte_column_to_display_column can go past the end,
      and similar edge cases.  */
   {
@@ -3645,10 +3658,13 @@ void test_cpp_utf8 ()
       /* 111122223456
 	 Byte columns.  */
 
-    ASSERT_EQ (5, cpp_display_width (str, 6));
-    ASSERT_EQ (105, cpp_byte_column_to_display_column (str, 6, 106));
-    ASSERT_EQ (10000, cpp_byte_column_to_display_column (NULL, 0, 10000));
-    ASSERT_EQ (0, cpp_byte_column_to_display_column (NULL, 10000, 0));
+    ASSERT_EQ (5, cpp_display_width (str, 6, def_tabstop));
+    ASSERT_EQ (105,
+	       cpp_byte_column_to_display_column (str, 6, 106, def_tabstop));
+    ASSERT_EQ (10000,
+	       cpp_byte_column_to_display_column (NULL, 0, 10000, def_tabstop));
+    ASSERT_EQ (0,
+	       cpp_byte_column_to_display_column (NULL, 10000, 0, def_tabstop));
   }
 
   /* Verify that cpp_display_column_to_byte_column can go past the end,
@@ -3662,21 +3678,25 @@ void test_cpp_utf8 ()
       /* 000000000000000000000000000000000111111
 	 111122223333444456666777788889999012345
 	 Byte columns.  */
-    ASSERT_EQ (4, cpp_display_column_to_byte_column (str, 15, 2));
-    ASSERT_EQ (15, cpp_display_column_to_byte_column (str, 15, 11));
-    ASSERT_EQ (115, cpp_display_column_to_byte_column (str, 15, 111));
-    ASSERT_EQ (10000, cpp_display_column_to_byte_column (NULL, 0, 10000));
-    ASSERT_EQ (0, cpp_display_column_to_byte_column (NULL, 10000, 0));
+    ASSERT_EQ (4, cpp_display_column_to_byte_column (str, 15, 2, def_tabstop));
+    ASSERT_EQ (15,
+	       cpp_display_column_to_byte_column (str, 15, 11, def_tabstop));
+    ASSERT_EQ (115,
+	       cpp_display_column_to_byte_column (str, 15, 111, def_tabstop));
+    ASSERT_EQ (10000,
+	       cpp_display_column_to_byte_column (NULL, 0, 10000, def_tabstop));
+    ASSERT_EQ (0,
+	       cpp_display_column_to_byte_column (NULL, 10000, 0, def_tabstop));
 
     /* Verify that we do not interrupt a UTF-8 sequence.  */
-    ASSERT_EQ (4, cpp_display_column_to_byte_column (str, 15, 1));
+    ASSERT_EQ (4, cpp_display_column_to_byte_column (str, 15, 1, def_tabstop));
 
     for (int byte_col = 1; byte_col <= 15; ++byte_col)
       {
-	const int disp_col = cpp_byte_column_to_display_column (str, 15,
-								byte_col);
-	const int byte_col2 = cpp_display_column_to_byte_column (str, 15,
-								 disp_col);
+	const int disp_col
+	  = cpp_byte_column_to_display_column (str, 15, byte_col, def_tabstop);
+	const int byte_col2
+	  = cpp_display_column_to_byte_column (str, 15, disp_col, def_tabstop);
 
 	/* If we ask for the display column in the middle of a UTF-8
 	   sequence, it will return the length of the partial sequence,
diff --git a/gcc/input.h b/gcc/input.h
--- a/gcc/input.h	2020-07-22 23:35:17.664388078 -0700
+++ b/gcc/input.h	2021-12-25 01:20:53.487636494 -0800
@@ -38,7 +38,9 @@ STATIC_ASSERT (BUILTINS_LOCATION < RESER
 
 extern bool is_location_from_builtin_token (location_t);
 extern expanded_location expand_location (location_t);
-extern int location_compute_display_column (expanded_location);
+
+extern int location_compute_display_column (expanded_location exploc,
+					    int tabstop);
 
 /* A class capturing the bounds of a buffer, to allow for run-time
    bounds-checking in a checked build.  */
diff --git a/gcc/opts.c b/gcc/opts.c
--- a/gcc/opts.c	2020-07-22 23:35:17.708388562 -0700
+++ b/gcc/opts.c	2021-12-25 01:20:53.487636494 -0800
@@ -2439,6 +2439,14 @@ common_handle_option (struct gcc_options
       dc->parseable_fixits_p = value;
       break;
 
+    case OPT_fdiagnostics_column_unit_:
+      dc->column_unit = (enum diagnostics_column_unit)value;
+      break;
+
+    case OPT_fdiagnostics_column_origin_:
+      dc->column_origin = value;
+      break;
+
     case OPT_fdiagnostics_show_cwe:
       dc->show_cwe = value;
       break;
@@ -2825,6 +2833,12 @@ common_handle_option (struct gcc_options
       check_alignment_argument (loc, arg, "functions");
       break;
 
+    case OPT_ftabstop_:
+      /* It is documented that we silently ignore silly values.  */
+      if (value >= 1 && value <= 100)
+	dc->tabstop = value;
+      break;
+
     default:
       /* If the flag was handled in a standard way, assume the lack of
 	 processing here is intentional.  */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-1.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-1.c
--- a/gcc/testsuite/c-c++-common/diagnostic-format-json-1.c	2020-07-22 23:35:17.908390765 -0700
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-1.c	2021-12-25 01:20:53.487636494 -0800
@@ -8,17 +8,22 @@
    We can't rely on any ordering of the keys.  */
 
 /* { dg-regexp "\"kind\": \"error\"" } */
+/* { dg-regexp "\"column-origin\": 1" } */
 /* { dg-regexp "\"message\": \"#error message\"" } */
 
 /* { dg-regexp "\"caret\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.c\"" } */
 /* { dg-regexp "\"line\": 4" } */
 /* { dg-regexp "\"column\": 2" } */
+/* { dg-regexp "\"display-column\": 2" } */
+/* { dg-regexp "\"byte-column\": 2" } */
 
 /* { dg-regexp "\"finish\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.c\"" } */
 /* { dg-regexp "\"line\": 4" } */
 /* { dg-regexp "\"column\": 6" } */
+/* { dg-regexp "\"display-column\": 6" } */
+/* { dg-regexp "\"byte-column\": 6" } */
 
 /* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
 /* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-2.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-2.c
--- a/gcc/testsuite/c-c++-common/diagnostic-format-json-2.c	2020-07-22 23:35:17.908390765 -0700
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-2.c	2021-12-25 01:20:53.487636494 -0800
@@ -8,6 +8,7 @@
    We can't rely on any ordering of the keys.  */
 
 /* { dg-regexp "\"kind\": \"warning\"" } */
+/* { dg-regexp "\"column-origin\": 1" } */
 /* { dg-regexp "\"message\": \"#warning message\"" } */
 /* { dg-regexp "\"option\": \"-Wcpp\"" } */
 /* { dg-regexp "\"option_url\": \"https:\[^\n\r\"\]*#index-Wcpp\"" } */
@@ -16,11 +17,15 @@
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.c\"" } */
 /* { dg-regexp "\"line\": 4" } */
 /* { dg-regexp "\"column\": 2" } */
+/* { dg-regexp "\"display-column\": 2" } */
+/* { dg-regexp "\"byte-column\": 2" } */
 
 /* { dg-regexp "\"finish\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.c\"" } */
 /* { dg-regexp "\"line\": 4" } */
 /* { dg-regexp "\"column\": 8" } */
+/* { dg-regexp "\"display-column\": 8" } */
+/* { dg-regexp "\"byte-column\": 8" } */
 
 /* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
 /* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-3.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-3.c
--- a/gcc/testsuite/c-c++-common/diagnostic-format-json-3.c	2020-07-22 23:35:17.908390765 -0700
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-3.c	2021-12-25 01:20:53.487636494 -0800
@@ -8,6 +8,7 @@
    We can't rely on any ordering of the keys.  */
 
 /* { dg-regexp "\"kind\": \"error\"" } */
+/* { dg-regexp "\"column-origin\": 1" } */
 /* { dg-regexp "\"message\": \"#warning message\"" } */
 /* { dg-regexp "\"option\": \"-Werror=cpp\"" } */
 /* { dg-regexp "\"option_url\": \"https:\[^\n\r\"\]*#index-Wcpp\"" } */
@@ -16,11 +17,15 @@
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.c\"" } */
 /* { dg-regexp "\"line\": 4" } */
 /* { dg-regexp "\"column\": 2" } */
+/* { dg-regexp "\"display-column\": 2" } */
+/* { dg-regexp "\"byte-column\": 2" } */
 
 /* { dg-regexp "\"finish\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.c\"" } */
 /* { dg-regexp "\"line\": 4" } */
 /* { dg-regexp "\"column\": 8" } */
+/* { dg-regexp "\"display-column\": 8" } */
+/* { dg-regexp "\"byte-column\": 8" } */
 
 /* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
 /* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-4.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-4.c
--- a/gcc/testsuite/c-c++-common/diagnostic-format-json-4.c	2020-07-22 23:35:17.908390765 -0700
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-4.c	2021-12-25 01:20:53.487636494 -0800
@@ -24,15 +24,20 @@ int test (void)
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
 /* { dg-regexp "\"line\": 8" } */
 /* { dg-regexp "\"column\": 5" } */
+/* { dg-regexp "\"display-column\": 5" } */
+/* { dg-regexp "\"byte-column\": 5" } */
 
 /* { dg-regexp "\"finish\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
 /* { dg-regexp "\"line\": 8" } */
 /* { dg-regexp "\"column\": 10" } */
+/* { dg-regexp "\"display-column\": 10" } */
+/* { dg-regexp "\"byte-column\": 10" } */
 
 /* The outer diagnostic.  */
 
 /* { dg-regexp "\"kind\": \"warning\"" } */
+/* { dg-regexp "\"column-origin\": 1" } */
 /* { dg-regexp "\"message\": \"this 'if' clause does not guard...\"" } */
 /* { dg-regexp "\"option\": \"-Wmisleading-indentation\"" } */
 /* { dg-regexp "\"option_url\": \"https:\[^\n\r\"\]*#index-Wmisleading-indentation\"" } */
@@ -41,11 +46,15 @@ int test (void)
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
 /* { dg-regexp "\"line\": 6" } */
 /* { dg-regexp "\"column\": 3" } */
+/* { dg-regexp "\"display-column\": 3" } */
+/* { dg-regexp "\"byte-column\": 3" } */
 
 /* { dg-regexp "\"finish\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-4.c\"" } */
 /* { dg-regexp "\"line\": 6" } */
 /* { dg-regexp "\"column\": 4" } */
+/* { dg-regexp "\"display-column\": 4" } */
+/* { dg-regexp "\"byte-column\": 4" } */
 
 /* More from the nested diagnostic (we can't guarantee what order the
    "file" keys are consumed).  */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-format-json-5.c b/gcc/testsuite/c-c++-common/diagnostic-format-json-5.c
--- a/gcc/testsuite/c-c++-common/diagnostic-format-json-5.c	2020-07-22 23:35:17.908390765 -0700
+++ b/gcc/testsuite/c-c++-common/diagnostic-format-json-5.c	2021-12-25 01:20:53.487636494 -0800
@@ -13,6 +13,7 @@ int test (struct s *ptr)
    We can't rely on any ordering of the keys.  */
 
 /* { dg-regexp "\"kind\": \"error\"" } */
+/* { dg-regexp "\"column-origin\": 1" } */
 /* { dg-regexp "\"message\": \".*\"" } */
 
 /* Verify fix-it hints.  */
@@ -23,11 +24,15 @@ int test (struct s *ptr)
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
 /* { dg-regexp "\"line\": 8" } */
 /* { dg-regexp "\"column\": 15" } */
+/* { dg-regexp "\"display-column\": 15" } */
+/* { dg-regexp "\"byte-column\": 15" } */
 
 /* { dg-regexp "\"next\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
 /* { dg-regexp "\"line\": 8" } */
 /* { dg-regexp "\"column\": 21" } */
+/* { dg-regexp "\"display-column\": 21" } */
+/* { dg-regexp "\"byte-column\": 21" } */
 
 /* { dg-regexp "\"fixits\": \[\[\{\}, \]*\]" } */
 
@@ -35,11 +40,15 @@ int test (struct s *ptr)
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
 /* { dg-regexp "\"line\": 8" } */
 /* { dg-regexp "\"column\": 15" } */
+/* { dg-regexp "\"display-column\": 15" } */
+/* { dg-regexp "\"byte-column\": 15" } */
 
 /* { dg-regexp "\"finish\": \{" } */
 /* { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-5.c\"" } */
 /* { dg-regexp "\"line\": 8" } */
 /* { dg-regexp "\"column\": 20" } */
+/* { dg-regexp "\"display-column\": 20" } */
+/* { dg-regexp "\"byte-column\": 20" } */
 
 /* { dg-regexp "\"locations\": \[\[\{\}, \]*\]" } */
 /* { dg-regexp "\"children\": \[\[\]\[\]\]" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-1.c b/gcc/testsuite/c-c++-common/diagnostic-units-1.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-1.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-1.c	2021-12-25 01:20:53.487636494 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdiagnostics-column-unit=byte -fshow-column -fdiagnostics-show-caret -Wmultichar" } */
+
+/* column units: bytes (via arg)
+   column origin: 1 (via default)
+   tabstop: 8 (via default) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "11: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c1 = 'c1';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+        int c2 = 'c2'; /* { dg-warning "18: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c2 = 'c2';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+        int c3 = 	'c3'; /* { dg-warning "19: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c3 =        'c3';
+                         ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-2.c b/gcc/testsuite/c-c++-common/diagnostic-units-2.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-2.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-2.c	2021-12-25 01:20:53.487636494 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdiagnostics-column-unit=display -fshow-column -fdiagnostics-show-caret -Wmultichar" } */
+
+/* column units: display (via arg)
+   column origin: 1 (via default)
+   tabstop: 8 (via default) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "18: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c1 = 'c1';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+        int c2 = 'c2'; /* { dg-warning "18: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c2 = 'c2';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+        int c3 = 	'c3'; /* { dg-warning "25: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c3 =        'c3';
+                         ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-3.c b/gcc/testsuite/c-c++-common/diagnostic-units-3.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-3.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-3.c	2021-12-25 01:20:53.487636494 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdiagnostics-column-unit=byte -fshow-column -fdiagnostics-show-caret -ftabstop=200 -Wmultichar" } */
+
+/* column units: bytes (via arg)
+   column origin: 1 (via fallback from overly large argument)
+   tabstop: 8 (via default) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "11: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c1 = 'c1';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+        int c2 = 'c2'; /* { dg-warning "18: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c2 = 'c2';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+        int c3 = 	'c3'; /* { dg-warning "19: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c3 =        'c3';
+                         ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-4.c b/gcc/testsuite/c-c++-common/diagnostic-units-4.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-4.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-4.c	2021-12-25 01:20:53.487636494 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdiagnostics-column-unit=byte -fshow-column -fdiagnostics-show-caret -fdiagnostics-column-origin=0 -Wmultichar" } */
+
+/* column units: bytes (via arg)
+   column origin: 0 (via arg)
+   tabstop: 8 (via default) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "10: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c1 = 'c1';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+        int c2 = 'c2'; /* { dg-warning "17: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c2 = 'c2';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+        int c3 = 	'c3'; /* { dg-warning "18: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c3 =        'c3';
+                         ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-5.c b/gcc/testsuite/c-c++-common/diagnostic-units-5.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-5.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-5.c	2021-12-25 01:20:53.491636427 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdiagnostics-column-unit=display -fshow-column -fdiagnostics-show-caret -fdiagnostics-column-origin=0 -Wmultichar" } */
+
+/* column units: display (via arg)
+   column origin: 0 (via arg)
+   tabstop: 8 (via default) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "17: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c1 = 'c1';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+        int c2 = 'c2'; /* { dg-warning "17: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c2 = 'c2';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+        int c3 = 	'c3'; /* { dg-warning "24: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c3 =        'c3';
+                         ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-6.c b/gcc/testsuite/c-c++-common/diagnostic-units-6.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-6.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-6.c	2021-12-25 01:20:53.491636427 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdiagnostics-column-unit=byte -fshow-column -fdiagnostics-show-caret -fdiagnostics-column-origin=100 -Wmultichar" } */
+
+/* column units: bytes (via arg)
+   column origin: 100 (via arg)
+   tabstop: 8 (via default) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "110: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c1 = 'c1';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+        int c2 = 'c2'; /* { dg-warning "117: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c2 = 'c2';
+                  ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+        int c3 = 	'c3'; /* { dg-warning "118: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+         int c3 =        'c3';
+                         ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-7.c b/gcc/testsuite/c-c++-common/diagnostic-units-7.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-7.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-7.c	2021-12-25 01:20:53.491636427 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fdiagnostics-column-unit=byte -fshow-column -fdiagnostics-show-caret -ftabstop=9 -Wmultichar" } */
+
+/* column units: bytes (via arg)
+   column origin: 1 (via default)
+   tabstop: 9 (via arg) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "11: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+          int c1 = 'c1';
+                   ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+         int c2 = 'c2'; /* { dg-warning "19: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+          int c2 = 'c2';
+                   ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+         int c3 = 	'c3'; /* { dg-warning "20: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+          int c3 =          'c3';
+                            ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/diagnostic-units-8.c b/gcc/testsuite/c-c++-common/diagnostic-units-8.c
--- a/gcc/testsuite/c-c++-common/diagnostic-units-8.c	1969-12-31 16:00:00.000000000 -0800
+++ b/gcc/testsuite/c-c++-common/diagnostic-units-8.c	2021-12-25 01:20:53.491636427 -0800
@@ -0,0 +1,28 @@
+/* { dg-do compile } */
+/* { dg-additional-options "-fshow-column -fdiagnostics-show-caret -ftabstop=9 -Wmultichar" } */
+
+/* column units: display (via default)
+   column origin: 1 (via default)
+   tabstop: 9 (via arg) */
+
+/* This line starts with a tab.  */
+	int c1 = 'c1'; /* { dg-warning "19: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+          int c1 = 'c1';
+                   ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces.  */
+         int c2 = 'c2'; /* { dg-warning "19: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+          int c2 = 'c2';
+                   ^~~~
+   { dg-end-multiline-output "" } */
+
+/* This line starts with <tabstop> spaces and has an internal tab after
+   a space.  */
+         int c3 = 	'c3'; /* { dg-warning "28: multi-character character constant" } */
+/* { dg-begin-multiline-output "" }
+          int c3 =          'c3';
+                            ^~~~
+   { dg-end-multiline-output "" } */
diff --git a/gcc/testsuite/c-c++-common/missing-close-symbol.c b/gcc/testsuite/c-c++-common/missing-close-symbol.c
--- a/gcc/testsuite/c-c++-common/missing-close-symbol.c	2020-07-22 23:35:17.912390810 -0700
+++ b/gcc/testsuite/c-c++-common/missing-close-symbol.c	2021-12-25 01:20:53.491636427 -0800
@@ -24,9 +24,9 @@ void test_static_assert_different_line (
   _Static_assert(sizeof(int) >= sizeof(char), /* { dg-message "to match this '\\('" } */
 		 "msg"; /* { dg-error "expected '\\)' before ';' token" } */
   /* { dg-begin-multiline-output "" }
-    "msg";
-         ^
-         )
+                  "msg";
+                       ^
+                       )
      { dg-end-multiline-output "" } */
   /* { dg-begin-multiline-output "" }
    _Static_assert(sizeof(int) >= sizeof(char),
diff --git a/gcc/testsuite/c-c++-common/Wmisleading-indentation-3.c b/gcc/testsuite/c-c++-common/Wmisleading-indentation-3.c
--- a/gcc/testsuite/c-c++-common/Wmisleading-indentation-3.c	2020-07-22 23:35:17.904390722 -0700
+++ b/gcc/testsuite/c-c++-common/Wmisleading-indentation-3.c	2021-12-25 01:20:53.487636494 -0800
@@ -36,20 +36,20 @@ int fn_6 (int a, int b, int c)
 	/* ... */
 	if ((err = foo (a)) != 0)
 		goto fail;
-	if ((err = foo (b)) != 0) /* { dg-message "2: this 'if' clause does not guard..." } */
+	if ((err = foo (b)) != 0) /* { dg-message "9: this 'if' clause does not guard..." } */
 		goto fail;
-		goto fail; /* { dg-message "3: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'" } */
+		goto fail; /* { dg-message "17: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'" } */
 	if ((err = foo (c)) != 0)
 		goto fail;
 	/* ... */
 
 /* { dg-begin-multiline-output "" }
-  if ((err = foo (b)) != 0)
-  ^~
+         if ((err = foo (b)) != 0)
+         ^~
    { dg-end-multiline-output "" } */
 /* { dg-begin-multiline-output "" }
-   goto fail;
-   ^~~~
+                 goto fail;
+                 ^~~~
    { dg-end-multiline-output "" } */
 
 fail:
diff --git a/gcc/testsuite/c-c++-common/Wmisleading-indentation.c b/gcc/testsuite/c-c++-common/Wmisleading-indentation.c
--- a/gcc/testsuite/c-c++-common/Wmisleading-indentation.c	2020-07-22 23:35:17.904390722 -0700
+++ b/gcc/testsuite/c-c++-common/Wmisleading-indentation.c	2021-12-25 01:20:53.487636494 -0800
@@ -65,9 +65,9 @@ int fn_6 (int a, int b, int c)
 	/* ... */
 	if ((err = foo (a)) != 0)
 		goto fail;
-	if ((err = foo (b)) != 0) /* { dg-message "2: this 'if' clause does not guard..." } */
+	if ((err = foo (b)) != 0) /* { dg-message "9: this 'if' clause does not guard..." } */
 		goto fail;
-		goto fail; /* { dg-message "3: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'" } */
+		goto fail; /* { dg-message "17: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'" } */
 	if ((err = foo (c)) != 0)
 		goto fail;
 	/* ... */
@@ -178,7 +178,7 @@ void fn_16_tabs (void)
     while (flagA)
       if (flagB) /* { dg-message "7: this 'if' clause does not guard..." } */
 	foo (0);
-	foo (1);/* { dg-message "2: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'" } */
+	foo (1);/* { dg-message "9: ...this statement, but the latter is misleadingly indented as if it were guarded by the 'if'" } */
 }
 
 void fn_17_spaces (void)
diff --git a/gcc/testsuite/gcc.dg/analyzer/malloc-paths-9.c b/gcc/testsuite/gcc.dg/analyzer/malloc-paths-9.c
--- a/gcc/testsuite/gcc.dg/analyzer/malloc-paths-9.c	2020-07-22 23:35:18.124393144 -0700
+++ b/gcc/testsuite/gcc.dg/analyzer/malloc-paths-9.c	2021-12-25 01:20:53.491636427 -0800
@@ -288,7 +288,7 @@ int test_3 (int x, int y)
     |      |     ~~~~~~~~~~
     |      |     |
     |      |     (4) ...to here
-    |   NN |      to dereference it above
+    |   NN |                    to dereference it above
     |   NN |   return *ptr;
     |      |          ~~~~
     |      |          |
diff --git a/gcc/testsuite/gcc.dg/bad-binary-ops.c b/gcc/testsuite/gcc.dg/bad-binary-ops.c
--- a/gcc/testsuite/gcc.dg/bad-binary-ops.c	2020-07-22 23:35:18.128393190 -0700
+++ b/gcc/testsuite/gcc.dg/bad-binary-ops.c	2021-12-25 01:20:53.491636427 -0800
@@ -35,10 +35,10 @@ int test_2 (void)
            ~~~~~~~~~~~~~~~~
            |
            struct s
-    + some_other_function ());
-    ^ ~~~~~~~~~~~~~~~~~~~~~~
-      |
-      struct t
+           + some_other_function ());
+           ^ ~~~~~~~~~~~~~~~~~~~~~~
+             |
+             struct t
    { dg-end-multiline-output "" } */
 }
 
diff --git a/gcc/testsuite/gcc.dg/format/branch-1.c b/gcc/testsuite/gcc.dg/format/branch-1.c
--- a/gcc/testsuite/gcc.dg/format/branch-1.c	2020-07-22 23:35:18.152393454 -0700
+++ b/gcc/testsuite/gcc.dg/format/branch-1.c	2021-12-25 01:20:53.491636427 -0800
@@ -10,7 +10,7 @@ foo (long l, int nfoo)
 {
   printf ((nfoo > 1) ? "%d foos" : "%d foo", nfoo);
   printf ((l > 1) ? "%d foos" /* { dg-warning "23:int" "wrong type in conditional expr" } */
-	          : "%d foo", l); /* { dg-warning "16:int" "wrong type in conditional expr" } */
+	          : "%d foo", l); /* { dg-warning "23:int" "wrong type in conditional expr" } */
   printf ((l > 1) ? "%ld foos" : "%d foo", l); /* { dg-warning "36:int" "wrong type in conditional expr" } */
   printf ((l > 1) ? "%d foos" : "%ld foo", l); /* { dg-warning "23:int" "wrong type in conditional expr" } */
   /* Should allow one case to have extra arguments.  */
diff --git a/gcc/testsuite/gcc.dg/format/pr79210.c b/gcc/testsuite/gcc.dg/format/pr79210.c
--- a/gcc/testsuite/gcc.dg/format/pr79210.c	2020-07-22 23:35:18.152393454 -0700
+++ b/gcc/testsuite/gcc.dg/format/pr79210.c	2021-12-25 01:20:53.491636427 -0800
@@ -20,4 +20,4 @@ LPFC_VPORT_ATTR_R(peer_port_login,
 		  "Allow peer ports on the same physical port to login to each "
 		  "other.");
 
-/* { dg-warning "6: format .%d. expects argument of type .int., but argument 4 has type .unsigned int. " "" { target *-*-* } .-12 } */
+/* { dg-warning "20: format .%d. expects argument of type .int., but argument 4 has type .unsigned int. " "" { target *-*-* } .-12 } */
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic-test-expressions-1.c b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-expressions-1.c
--- a/gcc/testsuite/gcc.dg/plugin/diagnostic-test-expressions-1.c	2020-07-22 23:35:18.172393674 -0700
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-expressions-1.c	2021-12-25 01:20:53.491636427 -0800
@@ -540,15 +540,15 @@ void test_builtin_types_compatible_p (un
   __emit_expression_range (0,
 			   f (i) + __builtin_types_compatible_p (long, int)); /* { dg-warning "range" } */
 /* { dg-begin-multiline-output "" }
-       f (i) + __builtin_types_compatible_p (long, int));
-       ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+                            f (i) + __builtin_types_compatible_p (long, int));
+                            ~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    { dg-end-multiline-output "" } */
 
   __emit_expression_range (0,
 			   __builtin_types_compatible_p (long, int) + f (i)); /* { dg-warning "range" } */
 /* { dg-begin-multiline-output "" }
-       __builtin_types_compatible_p (long, int) + f (i));
-       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
+                            __builtin_types_compatible_p (long, int) + f (i));
+                            ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~
    { dg-end-multiline-output "" } */
 }
 
@@ -671,8 +671,8 @@ void test_multiple_ordinary_maps (void)
 /* { dg-begin-multiline-output "" }
    __emit_expression_range (0, foo (0,
                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-        "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"));
-        ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+                                    "0123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789"));
+                                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    { dg-end-multiline-output "" } */
 
   /* Another expression that transitions between ordinary maps; this
@@ -685,8 +685,8 @@ void test_multiple_ordinary_maps (void)
 /* { dg-begin-multiline-output "" }
    __emit_expression_range (0, foo (0, "01234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789",
                                ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-        0));
-        ~~                      
+                                    0));
+                                    ~~
    { dg-end-multiline-output "" } */
 }
 
diff --git a/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-1.c b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-1.c
--- a/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-1.c	2020-07-22 23:35:18.172393674 -0700
+++ b/gcc/testsuite/gcc.dg/plugin/diagnostic-test-string-literals-1.c	2021-12-25 01:20:53.491636427 -0800
@@ -335,11 +335,11 @@ pr87652 (const char *stem, int counter)
 /* { dg-error "unable to read substring location: unable to read source line" "" { target c } 329 } */
 /* { dg-error "unable to read substring location: failed to get ordinary maps" "" { target c++ } 329 } */
 /* { dg-begin-multiline-output "" }
-     __emit_string_literal_range(__FILE__":%5d: " format, \
+     __emit_string_literal_range(__FILE__":%5d: " format,        \
                                  ^~~~~~~~
      { dg-end-multiline-output "" { target c } } */
 /* { dg-begin-multiline-output "" }
-     __emit_string_literal_range(__FILE__":%5d: " format, \
+     __emit_string_literal_range(__FILE__":%5d: " format,        \
                                  ^
      { dg-end-multiline-output "" { target c++ } } */
 
diff --git a/gcc/testsuite/gcc.dg/redecl-4.c b/gcc/testsuite/gcc.dg/redecl-4.c
--- a/gcc/testsuite/gcc.dg/redecl-4.c	2020-07-22 23:35:18.192393895 -0700
+++ b/gcc/testsuite/gcc.dg/redecl-4.c	2021-12-25 01:20:53.491636427 -0800
@@ -15,7 +15,7 @@ f (void)
     /* Should get format warnings even though the built-in declaration
        isn't "visible".  */
     printf (
-	    "%s", 1); /* { dg-warning "8:format" } */
+	    "%s", 1); /* { dg-warning "15:format" } */
     /* The type of strcmp here should have no prototype.  */
     if (0)
       strcmp (1);
diff --git a/gcc/testsuite/g++.dg/diagnostic/bad-binary-ops.C b/gcc/testsuite/g++.dg/diagnostic/bad-binary-ops.C
--- a/gcc/testsuite/g++.dg/diagnostic/bad-binary-ops.C	2020-07-22 23:35:17.972391472 -0700
+++ b/gcc/testsuite/g++.dg/diagnostic/bad-binary-ops.C	2021-12-25 01:20:53.491636427 -0800
@@ -33,10 +33,10 @@ int test_2 (void)
            ~~~~~~~~~~~~~~~~
                          |
                          s
-    + some_other_function ());
-    ^ ~~~~~~~~~~~~~~~~~~~~~~
-                          |
-                          t
+           + some_other_function ());
+           ^ ~~~~~~~~~~~~~~~~~~~~~~
+                                 |
+                                 t
    { dg-end-multiline-output "" } */
 }
 
diff --git a/gcc/testsuite/g++.dg/parse/error4.C b/gcc/testsuite/g++.dg/parse/error4.C
--- a/gcc/testsuite/g++.dg/parse/error4.C	2020-07-22 23:35:18.012391910 -0700
+++ b/gcc/testsuite/g++.dg/parse/error4.C	2021-12-25 01:20:53.491636427 -0800
@@ -7,4 +7,4 @@ struct X {
 		 int);
 };
 
-// { dg-error "4:'itn' has not been declared" "" { target *-*-* } 6 }
+// { dg-error "18:'itn' has not been declared" "" { target *-*-* } 6 }
diff --git a/gcc/testsuite/gfortran.dg/diagnostic-format-json-1.F90 b/gcc/testsuite/gfortran.dg/diagnostic-format-json-1.F90
--- a/gcc/testsuite/gfortran.dg/diagnostic-format-json-1.F90	2020-07-22 23:35:18.512397420 -0700
+++ b/gcc/testsuite/gfortran.dg/diagnostic-format-json-1.F90	2021-12-25 01:20:53.491636427 -0800
@@ -8,17 +8,22 @@
 ! We can't rely on any ordering of the keys.
 
 ! { dg-regexp "\"kind\": \"error\"" }
+! { dg-regexp "\"column-origin\": 1" }
 ! { dg-regexp "\"message\": \"#error message\"" }
 
 ! { dg-regexp "\"caret\": \{" }
 ! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.F90\"" }
 ! { dg-regexp "\"line\": 4" }
 ! { dg-regexp "\"column\": 2" }
+! { dg-regexp "\"display-column\": 2" }
+! { dg-regexp "\"byte-column\": 2" }
 
 ! { dg-regexp "\"finish\": \{" }
 ! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-1.F90\"" }
 ! { dg-regexp "\"line\": 4" }
 ! { dg-regexp "\"column\": 6" }
+! { dg-regexp "\"display-column\": 6" }
+! { dg-regexp "\"byte-column\": 6" }
 
 ! { dg-regexp "\"locations\": \[\[\{\}, \]*\]" }
 ! { dg-regexp "\"children\": \[\[\]\[\]\]" }
diff --git a/gcc/testsuite/gfortran.dg/diagnostic-format-json-2.F90 b/gcc/testsuite/gfortran.dg/diagnostic-format-json-2.F90
--- a/gcc/testsuite/gfortran.dg/diagnostic-format-json-2.F90	2020-07-22 23:35:18.512397420 -0700
+++ b/gcc/testsuite/gfortran.dg/diagnostic-format-json-2.F90	2021-12-25 01:20:53.491636427 -0800
@@ -8,6 +8,7 @@
 ! We can't rely on any ordering of the keys. 
 
 ! { dg-regexp "\"kind\": \"warning\"" }
+! { dg-regexp "\"column-origin\": 1" }
 ! { dg-regexp "\"message\": \"#warning message\"" }
 ! { dg-regexp "\"option\": \"-Wcpp\"" }
 ! { dg-regexp "\"option_url\": \"\[^\n\r\"\]*#index-Wcpp\"" }
@@ -16,11 +17,15 @@
 ! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.F90\"" }
 ! { dg-regexp "\"line\": 4" }
 ! { dg-regexp "\"column\": 2" }
+! { dg-regexp "\"display-column\": 2" }
+! { dg-regexp "\"byte-column\": 2" }
 
 ! { dg-regexp "\"finish\": \{" }
 ! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-2.F90\"" }
 ! { dg-regexp "\"line\": 4" }
 ! { dg-regexp "\"column\": 8" }
+! { dg-regexp "\"display-column\": 8" }
+! { dg-regexp "\"byte-column\": 8" }
 
 ! { dg-regexp "\"locations\": \[\[\{\}, \]*\]" }
 ! { dg-regexp "\"children\": \[\[\]\[\]\]" }
diff --git a/gcc/testsuite/gfortran.dg/diagnostic-format-json-3.F90 b/gcc/testsuite/gfortran.dg/diagnostic-format-json-3.F90
--- a/gcc/testsuite/gfortran.dg/diagnostic-format-json-3.F90	2020-07-22 23:35:18.512397420 -0700
+++ b/gcc/testsuite/gfortran.dg/diagnostic-format-json-3.F90	2021-12-25 01:20:53.491636427 -0800
@@ -8,6 +8,7 @@
 ! We can't rely on any ordering of the keys.
 
 ! { dg-regexp "\"kind\": \"error\"" }
+! { dg-regexp "\"column-origin\": 1" }
 ! { dg-regexp "\"message\": \"#warning message\"" }
 ! { dg-regexp "\"option\": \"-Werror=cpp\"" }
 ! { dg-regexp "\"option_url\": \"\[^\n\r\"\]*#index-Wcpp\"" }
@@ -16,11 +17,15 @@
 ! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.F90\"" }
 ! { dg-regexp "\"line\": 4" }
 ! { dg-regexp "\"column\": 2" }
+! { dg-regexp "\"display-column\": 2" }
+! { dg-regexp "\"byte-column\": 2" }
 
 ! { dg-regexp "\"finish\": \{" }
 ! { dg-regexp "\"file\": \"\[^\n\r\"\]*diagnostic-format-json-3.F90\"" }
 ! { dg-regexp "\"line\": 4" }
 ! { dg-regexp "\"column\": 8" }
+! { dg-regexp "\"display-column\": 8" }
+! { dg-regexp "\"byte-column\": 8" }
 
 ! { dg-regexp "\"locations\": \[\[\{\}, \]*\]" }
 ! { dg-regexp "\"children\": \[\[\]\[\]\]" }
diff --git a/gcc/testsuite/go.dg/arrayclear.go b/gcc/testsuite/go.dg/arrayclear.go
--- a/gcc/testsuite/go.dg/arrayclear.go	2020-07-22 23:35:18.588398257 -0700
+++ b/gcc/testsuite/go.dg/arrayclear.go	2021-12-25 01:20:53.491636427 -0800
@@ -1,5 +1,8 @@
 // { dg-do compile }
 // { dg-options "-fgo-debug-optimization" }
+// This comment is necessary to work around a dejagnu bug. Otherwise, the
+// column of the second error message would equal the row of the first one, and
+// since the errors are also identical, dejagnu is not able to distinguish them.
 
 package p
 
diff --git a/gcc/testsuite/g++.old-deja/g++.brendan/crash11.C b/gcc/testsuite/g++.old-deja/g++.brendan/crash11.C
--- a/gcc/testsuite/g++.old-deja/g++.brendan/crash11.C	2020-07-22 23:35:18.048392308 -0700
+++ b/gcc/testsuite/g++.old-deja/g++.brendan/crash11.C	2021-12-25 01:20:53.491636427 -0800
@@ -9,13 +9,13 @@ class A {
 	int	h;
 	A() { i=10; j=20; }
 	virtual void f1() { printf("i=%d j=%d\n",i,j); }
-	friend virtual void f2() { printf("i=%d j=%d\n",i,j); } // { dg-error "9:virtual functions cannot be friends" }
+	friend virtual void f2() { printf("i=%d j=%d\n",i,j); } // { dg-error "16:virtual functions cannot be friends" }
 };
 
 class B : public A {
     public:
 	virtual void f1() { printf("i=%d j=%d\n",i,j); }// { dg-error "" }  member.*// ERROR -  member.*
-	friend virtual void f2() { printf("i=%d j=%d\n",i,j); }  // { dg-error "9:virtual functions cannot be friends" }
+	friend virtual void f2() { printf("i=%d j=%d\n",i,j); }  // { dg-error "16:virtual functions cannot be friends" }
 // { dg-error "private" "" { target *-*-* } .-1 }
 };
 
diff --git a/gcc/testsuite/g++.old-deja/g++.pt/overload2.C b/gcc/testsuite/g++.old-deja/g++.pt/overload2.C
--- a/gcc/testsuite/g++.old-deja/g++.pt/overload2.C	2020-07-22 23:35:18.072392572 -0700
+++ b/gcc/testsuite/g++.old-deja/g++.pt/overload2.C	2021-12-25 01:20:53.491636427 -0800
@@ -12,5 +12,5 @@ int
 main()
 {
 	C<char*>	c;
-	char*		p = Z(c.O); //{ dg-error "13:'Z' was not declared" } ambiguous c.O
+	char*		p = Z(c.O); //{ dg-error "29:'Z' was not declared" } ambiguous c.O
 }
diff --git a/gcc/testsuite/g++.old-deja/g++.robertl/eb109.C b/gcc/testsuite/g++.old-deja/g++.robertl/eb109.C
--- a/gcc/testsuite/g++.old-deja/g++.robertl/eb109.C	2020-07-22 23:35:18.076392617 -0700
+++ b/gcc/testsuite/g++.old-deja/g++.robertl/eb109.C	2021-12-25 01:20:53.491636427 -0800
@@ -48,8 +48,8 @@ ostream& operator<<(ostream& os, Graph<V
 
         // The compiler does not like this line!!!!!!
         typename Graph<VertexType, EdgeType>::Successor::iterator
-	  startN = G[i].second.begin(), // { dg-error "14:no match" } no index operator
-	  endN   = G[i].second.end();  // { dg-error "14:no match" } no index operator
+	  startN = G[i].second.begin(), // { dg-error "21:no match" } no index operator
+	  endN   = G[i].second.end();  // { dg-error "21:no match" } no index operator
 
         while(startN != endN)
         {
diff --git a/gcc/tree-diagnostic-path.cc b/gcc/tree-diagnostic-path.cc
--- a/gcc/tree-diagnostic-path.cc	2020-07-22 23:35:18.628398698 -0700
+++ b/gcc/tree-diagnostic-path.cc	2021-12-25 01:20:53.491636427 -0800
@@ -493,7 +493,7 @@ default_tree_diagnostic_path_printer (di
    doesn't have access to trees (for m_fndecl).  */
 
 json::value *
-default_tree_make_json_for_path (diagnostic_context *,
+default_tree_make_json_for_path (diagnostic_context *context,
 				 const diagnostic_path *path)
 {
   json::array *path_array = new json::array ();
@@ -504,7 +504,8 @@ default_tree_make_json_for_path (diagnos
       json::object *event_obj = new json::object ();
       if (event.get_location ())
 	event_obj->set ("location",
-			json_from_expanded_location (event.get_location ()));
+			json_from_expanded_location (context,
+						     event.get_location ()));
       label_text event_text (event.get_desc (false));
       event_obj->set ("description", new json::string (event_text.m_buffer));
       event_text.maybe_free ();
diff --git a/libcpp/charset.c b/libcpp/charset.c
--- a/libcpp/charset.c	2020-07-22 23:35:18.712399623 -0700
+++ b/libcpp/charset.c	2021-12-25 01:20:53.491636427 -0800
@@ -2276,49 +2276,90 @@ cpp_string_location_reader::get_next ()
   return result;
 }
 
-/* Helper for cpp_byte_column_to_display_column and its inverse.  Given a
-   pointer to a UTF-8-encoded character, compute its display width.  *INBUFP
-   points on entry to the start of the UTF-8 encoding of the character, and
-   is updated to point just after the last byte of the encoding.  *INBYTESLEFTP
-   contains on entry the remaining size of the buffer into which *INBUFP
-   points, and this is also updated accordingly.  If *INBUFP does not
+cpp_display_width_computation::
+cpp_display_width_computation (const char *data, int data_length, int tabstop) :
+  m_begin (data),
+  m_next (m_begin),
+  m_bytes_left (data_length),
+  m_tabstop (tabstop),
+  m_display_cols (0)
+{
+  gcc_assert (m_tabstop > 0);
+}
+
+
+/* The main implementation function for class cpp_display_width_computation.
+   m_next points on entry to the start of the UTF-8 encoding of the next
+   character, and is updated to point just after the last byte of the encoding.
+   m_bytes_left contains on entry the remaining size of the buffer into which
+   m_next points, and this is also updated accordingly.  If m_next does not
    point to a valid UTF-8-encoded sequence, then it will be treated as a single
-   byte with display width 1.  */
+   byte with display width 1.  m_cur_display_col is the current display column,
+   relative to which tab stops should be expanded.  Returns the display width of
+   the codepoint just processed.  */
 
-static inline int
-compute_next_display_width (const uchar **inbufp, size_t *inbytesleftp)
+int
+cpp_display_width_computation::process_next_codepoint ()
 {
   cppchar_t c;
-  if (one_utf8_to_cppchar (inbufp, inbytesleftp, &c) != 0)
+  int next_width;
+
+  if (*m_next == '\t')
+    {
+      ++m_next;
+      --m_bytes_left;
+      next_width = m_tabstop - (m_display_cols % m_tabstop);
+    }
+  else if (one_utf8_to_cppchar ((const uchar **) &m_next, &m_bytes_left, &c)
+	   != 0)
     {
       /* Input is not convertible to UTF-8.  This could be fine, e.g. in a
 	 string literal, so don't complain.  Just treat it as if it has a width
 	 of one.  */
-      ++*inbufp;
-      --*inbytesleftp;
-      return 1;
+      ++m_next;
+      --m_bytes_left;
+      next_width = 1;
+    }
+  else
+    {
+      /*  one_utf8_to_cppchar() has updated m_next and m_bytes_left for us.  */
+      next_width = cpp_wcwidth (c);
     }
 
-  /*  one_utf8_to_cppchar() has updated inbufp and inbytesleftp for us.  */
-  return cpp_wcwidth (c);
+  m_display_cols += next_width;
+  return next_width;
+}
+
+/*  Utility to advance the byte stream by the minimum amount needed to consume
+    N display columns.  Returns the number of display columns that were
+    actually skipped.  This could be less than N, if there was not enough data,
+    or more than N, if the last character to be skipped had a sufficiently large
+    display width.  */
+int
+cpp_display_width_computation::advance_display_cols (int n)
+{
+  const int start = m_display_cols;
+  const int target = start + n;
+  while (m_display_cols < target && !done ())
+    process_next_codepoint ();
+  return m_display_cols - start;
 }
 
 /*  For the string of length DATA_LENGTH bytes that begins at DATA, compute
     how many display columns are occupied by the first COLUMN bytes.  COLUMN
     may exceed DATA_LENGTH, in which case the phantom bytes at the end are
-    treated as if they have display width 1.  */
+    treated as if they have display width 1.  Tabs are expanded to the next tab
+    stop, relative to the start of DATA.  */
 
 int
 cpp_byte_column_to_display_column (const char *data, int data_length,
-				   int column)
+				   int column, int tabstop)
 {
-  int display_col = 0;
-  const uchar *udata = (const uchar *) data;
   const int offset = MAX (0, column - data_length);
-  size_t inbytesleft = column - offset;
-  while (inbytesleft)
-    display_col += compute_next_display_width (&udata, &inbytesleft);
-  return display_col + offset;
+  cpp_display_width_computation dw (data, column - offset, tabstop);
+  while (!dw.done ())
+    dw.process_next_codepoint ();
+  return dw.display_cols_processed () + offset;
 }
 
 /*  For the string of length DATA_LENGTH bytes that begins at DATA, compute
@@ -2328,14 +2369,11 @@ cpp_byte_column_to_display_column (const
 
 int
 cpp_display_column_to_byte_column (const char *data, int data_length,
-				   int display_col)
+				   int display_col, int tabstop)
 {
-  int column = 0;
-  const uchar *udata = (const uchar *) data;
-  size_t inbytesleft = data_length;
-  while (column < display_col && inbytesleft)
-      column += compute_next_display_width (&udata, &inbytesleft);
-  return data_length - inbytesleft + MAX (0, display_col - column);
+  cpp_display_width_computation dw (data, data_length, tabstop);
+  const int avail_display = dw.advance_display_cols (display_col);
+  return dw.bytes_processed () + MAX (0, display_col - avail_display);
 }
 
 /* Our own version of wcwidth().  We don't use the actual wcwidth() in glibc,
diff --git a/libcpp/include/cpplib.h b/libcpp/include/cpplib.h
--- a/libcpp/include/cpplib.h	2020-07-22 23:35:18.712399623 -0700
+++ b/libcpp/include/cpplib.h	2021-12-25 01:20:53.491636427 -0800
@@ -312,9 +312,6 @@ enum cpp_normalize_level {
    carries all the options visible to the command line.  */
 struct cpp_options
 {
-  /* Characters between tab stops.  */
-  unsigned int tabstop;
-
   /* The language we're preprocessing.  */
   enum c_lang lang;
 
@@ -1322,14 +1319,43 @@ extern const char * cpp_get_userdef_suff
   (const cpp_token *);
 
 /* In charset.c */
+
+/* A class to manage the state while converting a UTF-8 sequence to cppchar_t
+   and computing the display width one character at a time.  */
+class cpp_display_width_computation {
+ public:
+  cpp_display_width_computation (const char *data, int data_length,
+				 int tabstop);
+  const char *next_byte () const { return m_next; }
+  int bytes_processed () const { return m_next - m_begin; }
+  int bytes_left () const { return m_bytes_left; }
+  bool done () const { return !bytes_left (); }
+  int display_cols_processed () const { return m_display_cols; }
+
+  int process_next_codepoint ();
+  int advance_display_cols (int n);
+
+ private:
+  const char *const m_begin;
+  const char *m_next;
+  size_t m_bytes_left;
+  const int m_tabstop;
+  int m_display_cols;
+};
+
+/* Convenience functions that are simple use cases for class
+   cpp_display_width_computation.  Tab characters will be expanded to spaces
+   as determined by TABSTOP.  */
 int cpp_byte_column_to_display_column (const char *data, int data_length,
-				       int column);
-inline int cpp_display_width (const char *data, int data_length)
+				       int column, int tabstop);
+inline int cpp_display_width (const char *data, int data_length,
+			      int tabstop)
 {
-    return cpp_byte_column_to_display_column (data, data_length, data_length);
+  return cpp_byte_column_to_display_column (data, data_length, data_length,
+					    tabstop);
 }
 int cpp_display_column_to_byte_column (const char *data, int data_length,
-				       int display_col);
+				       int display_col, int tabstop);
 int cpp_wcwidth (cppchar_t c);
 
 #endif /* ! LIBCPP_CPPLIB_H */
diff --git a/libcpp/init.c b/libcpp/init.c
--- a/libcpp/init.c	2020-07-22 23:35:18.712399623 -0700
+++ b/libcpp/init.c	2021-12-25 01:20:53.491636427 -0800
@@ -190,7 +190,6 @@ cpp_create_reader (enum c_lang lang, cpp
   CPP_OPTION (pfile, discard_comments) = 1;
   CPP_OPTION (pfile, discard_comments_in_macro_exp) = 1;
   CPP_OPTION (pfile, max_include_depth) = 200;
-  CPP_OPTION (pfile, tabstop) = 8;
   CPP_OPTION (pfile, operator_names) = 1;
   CPP_OPTION (pfile, warn_trigraphs) = 2;
   CPP_OPTION (pfile, warn_endif_labels) = 1;