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From 96f71c147809df7880100edeecb197d5d5095206 Mon Sep 17 00:00:00 2001
From: Victor Kamensky <kamensky@cisco.com>
Date: Fri, 31 Jan 2020 09:39:44 -0800
Subject: [PATCH] mips: vdso: fix 'jalr $t9' crash in vdso code
Observed that when kernel is built with Yocto mips64-poky-linux-gcc,
and mips64-poky-linux-gnun32-gcc toolchain, resuling vdso contains
'jalr $t9' instructions in its code and since in vdso case nobody
sets GOT table code crashes when instruction reached. On other hand
observed that when kernel is built mips-poky-linux-gcc toolchain, the
same 'jalr $t9' instruction are replaced with PC relative function
calls using 'bal' instructions.
The difference boils down to -mrelax-pic-calls and -mexplicit-relocs
gcc options that gets different default values depending on gcc
target triplets and corresponding binutils. -mrelax-pic-calls got
enabled by default only in mips-poky-linux-gcc case. MIPS binuitls
ld relies on R_MIPS_JALR relocation to convert 'jalr $t9' into 'bal'
and such relocation is generated only if -mrelax-pic-calls option
is on.
Solution call out -mrelax-pic-calls and -mexplicit-relocs options
explicitely while compiling MIPS vdso code. That would get correct
and consitent between different toolchains behavior.
Reported-by: Bruce Ashfield <bruce.ashfield@gmail.com>
Signed-off-by: Victor Kamensky <kamensky@cisco.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>
---
arch/mips/vdso/Makefile | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile
index 996a934ece7d..25b5adee5ade 100644
--- a/arch/mips/vdso/Makefile
+++ b/arch/mips/vdso/Makefile
@@ -31,7 +31,9 @@ cflags-vdso := $(ccflags-vdso) \
-O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \
-fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \
$(call cc-option, -fno-asynchronous-unwind-tables) \
- $(call cc-option, -fno-stack-protector)
+ $(call cc-option, -fno-stack-protector) \
+ $(call cc-option, -mrelax-pic-calls) \
+ $(call cc-option, -mexplicit-relocs)
aflags-vdso := $(ccflags-vdso) \
-D__ASSEMBLY__ -Wa,-gdwarf-2
--
2.19.1
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