From: Victor Kamensky kamensky@cisco.com
[ Upstream commit d3f703c4359ff06619b2322b91f69710453e6b6d ]
Observed that when kernel is built with Yocto mips64-poky-linux-gcc, and mips64-poky-linux-gnun32-gcc toolchain, resulting 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 binutils 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.
Please note 'jalr t9' conversion to 'bal' can happen only to static functions. These static PIC calls use mips local GOT entries that are supposed to be filled with start of DSO value by run-time linker (missing in VDSO case) and they do not have dynamic relocations. Global mips GOT entries must have dynamic relocations and they should be prevented by cmd_vdso_check Makefile rule.
Solution call out -mrelax-pic-calls and -mexplicit-relocs options explicitly while compiling MIPS vdso code. That would get correct and consistent between different toolchains behaviour.
Reported-by: Bruce Ashfield bruce.ashfield@gmail.com Signed-off-by: Victor Kamensky kamensky@cisco.com Signed-off-by: Paul Burton paulburton@kernel.org Cc: linux-mips@vger.kernel.org Cc: Ralf Baechle ralf@linux-mips.org Cc: James Hogan jhogan@kernel.org Cc: Vincenzo Frascino vincenzo.frascino@arm.com Cc: richard.purdie@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/mips/vdso/Makefile | 1 + 1 file changed, 1 insertion(+)
diff --git a/arch/mips/vdso/Makefile b/arch/mips/vdso/Makefile index 996a934ece7d6..3fa4bbe1bae53 100644 --- a/arch/mips/vdso/Makefile +++ b/arch/mips/vdso/Makefile @@ -29,6 +29,7 @@ endif cflags-vdso := $(ccflags-vdso) \ $(filter -W%,$(filter-out -Wa$(comma)%,$(KBUILD_CFLAGS))) \ -O3 -g -fPIC -fno-strict-aliasing -fno-common -fno-builtin -G 0 \ + -mrelax-pic-calls -mexplicit-relocs \ -fno-stack-protector -fno-jump-tables -DDISABLE_BRANCH_PROFILING \ $(call cc-option, -fno-asynchronous-unwind-tables) \ $(call cc-option, -fno-stack-protector)