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+/*
+ * arch/arm64/kernel/entry-ftrace.S
+ *
+ * Copyright (C) 2013 Linaro Limited
+ * Author: AKASHI Takahiro <takahiro.akashi@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+#include <asm/ftrace.h>
+#include <asm/insn.h>
+
+/*
+ * Gcc with -pg will put the following code in the beginning of each function:
+ * mov x0, x30
+ * bl _mcount
+ * [function's body ...]
+ * "bl _mcount" may be replaced to "bl ftrace_caller" or NOP if dynamic
+ * ftrace is enabled.
+ *
+ * Please note that x0 as an argument will not be used here because we can
+ * get lr(x30) of instrumented function at any time by winding up call stack
+ * as long as the kernel is compiled without -fomit-frame-pointer.
+ * (or CONFIG_FRAME_POINTER, this is forced on arm64)
+ *
+ * stack layout after mcount_enter in _mcount():
+ *
+ * current sp/fp => 0:+-----+
+ * in _mcount() | x29 | -> instrumented function's fp
+ * +-----+
+ * | x30 | -> _mcount()'s lr (= instrumented function's pc)
+ * old sp => +16:+-----+
+ * when instrumented | |
+ * function calls | ... |
+ * _mcount() | |
+ * | |
+ * instrumented => +xx:+-----+
+ * function's fp | x29 | -> parent's fp
+ * +-----+
+ * | x30 | -> instrumented function's lr (= parent's pc)
+ * +-----+
+ * | ... |
+ */
+
+ .macro mcount_enter
+ stp x29, x30, [sp, #-16]!
+ mov x29, sp
+ .endm
+
+ .macro mcount_exit
+ ldp x29, x30, [sp], #16
+ ret
+ .endm
+
+ .macro mcount_adjust_addr rd, rn
+ sub \rd, \rn, #AARCH64_INSN_SIZE
+ .endm
+
+ /* for instrumented function's parent */
+ .macro mcount_get_parent_fp reg
+ ldr \reg, [x29]
+ ldr \reg, [\reg]
+ .endm
+
+ /* for instrumented function */
+ .macro mcount_get_pc0 reg
+ mcount_adjust_addr \reg, x30
+ .endm
+
+ .macro mcount_get_pc reg
+ ldr \reg, [x29, #8]
+ mcount_adjust_addr \reg, \reg
+ .endm
+
+ .macro mcount_get_lr reg
+ ldr \reg, [x29]
+ ldr \reg, [\reg, #8]
+ mcount_adjust_addr \reg, \reg
+ .endm
+
+ .macro mcount_get_lr_addr reg
+ ldr \reg, [x29]
+ add \reg, \reg, #8
+ .endm
+
+#ifndef CONFIG_DYNAMIC_FTRACE
+/*
+ * void _mcount(unsigned long return_address)
+ * @return_address: return address to instrumented function
+ *
+ * This function makes calls, if enabled, to:
+ * - tracer function to probe instrumented function's entry,
+ * - ftrace_graph_caller to set up an exit hook
+ */
+ENTRY(_mcount)
+#ifdef CONFIG_HAVE_FUNCTION_TRACE_MCOUNT_TEST
+ ldr x0, =ftrace_trace_stop
+ ldr x0, [x0] // if ftrace_trace_stop
+ ret // return;
+#endif
+ mcount_enter
+
+ ldr x0, =ftrace_trace_function
+ ldr x2, [x0]
+ adr x0, ftrace_stub
+ cmp x0, x2 // if (ftrace_trace_function
+ b.eq skip_ftrace_call // != ftrace_stub) {
+
+ mcount_get_pc x0 // function's pc
+ mcount_get_lr x1 // function's lr (= parent's pc)
+ blr x2 // (*ftrace_trace_function)(pc, lr);
+
+#ifndef CONFIG_FUNCTION_GRAPH_TRACER
+skip_ftrace_call: // return;
+ mcount_exit // }
+#else
+ mcount_exit // return;
+ // }
+skip_ftrace_call:
+ ldr x1, =ftrace_graph_return
+ ldr x2, [x1] // if ((ftrace_graph_return
+ cmp x0, x2 // != ftrace_stub)
+ b.ne ftrace_graph_caller
+
+ ldr x1, =ftrace_graph_entry // || (ftrace_graph_entry
+ ldr x2, [x1] // != ftrace_graph_entry_stub))
+ ldr x0, =ftrace_graph_entry_stub
+ cmp x0, x2
+ b.ne ftrace_graph_caller // ftrace_graph_caller();
+
+ mcount_exit
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
+ENDPROC(_mcount)
+
+#else /* CONFIG_DYNAMIC_FTRACE */
+/*
+ * _mcount() is used to build the kernel with -pg option, but all the branch
+ * instructions to _mcount() are replaced to NOP initially at kernel start up,
+ * and later on, NOP to branch to ftrace_caller() when enabled or branch to
+ * NOP when disabled per-function base.
+ */
+ENTRY(_mcount)
+ ret
+ENDPROC(_mcount)
+
+/*
+ * void ftrace_caller(unsigned long return_address)
+ * @return_address: return address to instrumented function
+ *
+ * This function is a counterpart of _mcount() in 'static' ftrace, and
+ * makes calls to:
+ * - tracer function to probe instrumented function's entry,
+ * - ftrace_graph_caller to set up an exit hook
+ */
+ENTRY(ftrace_caller)
+ mcount_enter
+
+ mcount_get_pc0 x0 // function's pc
+ mcount_get_lr x1 // function's lr
+
+ .global ftrace_call
+ftrace_call: // tracer(pc, lr);
+ nop // This will be replaced with "bl xxx"
+ // where xxx can be any kind of tracer.
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ .global ftrace_graph_call
+ftrace_graph_call: // ftrace_graph_caller();
+ nop // If enabled, this will be replaced
+ // "b ftrace_graph_caller"
+#endif
+
+ mcount_exit
+ENDPROC(ftrace_caller)
+#endif /* CONFIG_DYNAMIC_FTRACE */
+
+ENTRY(ftrace_stub)
+ ret
+ENDPROC(ftrace_stub)
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+/*
+ * void ftrace_graph_caller(void)
+ *
+ * Called from _mcount() or ftrace_caller() when function_graph tracer is
+ * selected.
+ * This function w/ prepare_ftrace_return() fakes link register's value on
+ * the call stack in order to intercept instrumented function's return path
+ * and run return_to_handler() later on its exit.
+ */
+ENTRY(ftrace_graph_caller)
+ mcount_get_lr_addr x0 // pointer to function's saved lr
+ mcount_get_pc x1 // function's pc
+ mcount_get_parent_fp x2 // parent's fp
+ bl prepare_ftrace_return // prepare_ftrace_return(&lr, pc, fp)
+
+ mcount_exit
+ENDPROC(ftrace_graph_caller)
+
+/*
+ * void return_to_handler(void)
+ *
+ * Run ftrace_return_to_handler() before going back to parent.
+ * @fp is checked against the value passed by ftrace_graph_caller()
+ * only when CONFIG_HAVE_FUNCTION_GRAPH_FP_TEST is enabled.
+ */
+ENTRY(return_to_handler)
+ str x0, [sp, #-16]!
+ mov x0, x29 // parent's fp
+ bl ftrace_return_to_handler// addr = ftrace_return_to_hander(fp);
+ mov x30, x0 // restore the original return address
+ ldr x0, [sp], #16
+ ret
+END(return_to_handler)
+#endif /* CONFIG_FUNCTION_GRAPH_TRACER */
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