The VDSO Makefile filters CFLAGS to select a subset which it uses whilst building the VDSO ELF. One of the flags it allows through is the -march= flag that selects the architecture/ISA to target.

Unfortunately in cases where CONFIG_CPU_MIPS32_R{1,2}=y and the toolchain defaults to building for MIPS64, the main MIPS Makefile ends up using the short-form -<arch> flags in cflags-y. This is because the calls to cc-option always fail to use the long-form -march=<arch> flag due to the lack of an -mabi=<abi> flag in KBUILD_CFLAGS at the point where the cc-option function is executed. The resulting GCC invocation is something like:

$ mips64-linux-gcc -Werror -march=mips32r2 -c -x c /dev/null -o tmp cc1: error: '-march=mips32r2' is not compatible with the selected ABI

These short-form -<arch> flags are dropped by the VDSO Makefile's filtering, and so we attempt to build the VDSO without specifying any architecture. This results in an attempt to build the VDSO using whatever the compiler's default architecture is, regardless of whether that is suitable for the kernel configuration.

One encountered build failure resulting from this mismatch is a rejection of the sync instruction if the kernel is configured for a MIPS32 or MIPS64 r1 or r2 target but the toolchain defaults to an older architecture revision such as MIPS1 which did not include the sync instruction:

CC arch/mips/vdso/gettimeofday.o /tmp/ccGQKoOj.s: Assembler messages: /tmp/ccGQKoOj.s:273: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:329: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:520: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:714: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1009: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1066: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1114: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1279: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1334: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1374: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1459: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1514: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:1814: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:2002: Error: opcode not supported on this processor: mips1 (mips1) `sync' /tmp/ccGQKoOj.s:2066: Error: opcode not supported on this processor: mips1 (mips1) `sync' make[2]: *** [scripts/Makefile.build:318: arch/mips/vdso/gettimeofday.o] Error 1 make[1]: *** [scripts/Makefile.build:558: arch/mips/vdso] Error 2 make[1]: *** Waiting for unfinished jobs....

This can be reproduced for example by attempting to build pistachio_defconfig using Arnd's GCC 8.1.0 mips64 toolchain from kernel.org:

https://mirrors.edge.kernel.org/pub/tools/crosstool/files/bin/x86_64/8.1.0/x...

Resolve this problem by using the long-form -march=<arch> in all cases, which makes it through the arch/mips/vdso/Makefile's filtering & is thus consistently used to build both the kernel proper & the VDSO.

The use of cc-option to prefer the long-form & fall back to the short-form flags makes no sense since the short-form is just an abbreviation for the also-supported long-form in all GCC versions that we support building with. This means there is no case in which we have to use the short-form -<arch> flags, so we can simply remove them.

The manual redefinition of _MIPS_ISA is removed naturally along with the use of the short-form flags that it accompanied, and whilst here we remove the separate assembler ISA selection. I suspect that both of these were only required due to the mips32 vs mips2 mismatch that was introduced by commit 59b3e8e9aac6 ("[MIPS] Makefile crapectomy.") and fixed but not cleaned up by commit 9200c0b2a07c ("[MIPS] Fix Makefile bugs for MIPS32/MIPS64 R1 and R2.").

I've marked this for backport as far as v4.4 where the MIPS VDSO was introduced. In earlier kernels there should be no ill effect to using the short-form flags.

Signed-off-by: Paul Burton paul.burton@mips.com Cc: James Hogan jhogan@kernel.org Cc: Ralf Baechle ralf@linux-mips.org Cc: linux-mips@linux-mips.org Cc: stable@vger.kernel.org # v4.4+ ---

arch/mips/Makefile | 12 ++++-------- 1 file changed, 4 insertions(+), 8 deletions(-)

diff --git a/arch/mips/Makefile b/arch/mips/Makefile index e2122cca4ae2..1e98d22ec119 100644 --- a/arch/mips/Makefile +++ b/arch/mips/Makefile @@ -155,15 +155,11 @@ cflags-$(CONFIG_CPU_R4300) += -march=r4300 -Wa,--trap cflags-$(CONFIG_CPU_VR41XX) += -march=r4100 -Wa,--trap cflags-$(CONFIG_CPU_R4X00) += -march=r4600 -Wa,--trap cflags-$(CONFIG_CPU_TX49XX) += -march=r4600 -Wa,--trap -cflags-$(CONFIG_CPU_MIPS32_R1) += $(call cc-option,-march=mips32,-mips32 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS32) \ - -Wa,-mips32 -Wa,--trap -cflags-$(CONFIG_CPU_MIPS32_R2) += $(call cc-option,-march=mips32r2,-mips32r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS32) \ - -Wa,-mips32r2 -Wa,--trap +cflags-$(CONFIG_CPU_MIPS32_R1) += -march=mips32 -Wa,--trap +cflags-$(CONFIG_CPU_MIPS32_R2) += -march=mips32r2 -Wa,--trap cflags-$(CONFIG_CPU_MIPS32_R6) += -march=mips32r6 -Wa,--trap -modd-spreg -cflags-$(CONFIG_CPU_MIPS64_R1) += $(call cc-option,-march=mips64,-mips64 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64) \ - -Wa,-mips64 -Wa,--trap -cflags-$(CONFIG_CPU_MIPS64_R2) += $(call cc-option,-march=mips64r2,-mips64r2 -U_MIPS_ISA -D_MIPS_ISA=_MIPS_ISA_MIPS64) \ - -Wa,-mips64r2 -Wa,--trap +cflags-$(CONFIG_CPU_MIPS64_R1) += -march=mips64 -Wa,--trap +cflags-$(CONFIG_CPU_MIPS64_R2) += -march=mips64r2 -Wa,--trap cflags-$(CONFIG_CPU_MIPS64_R6) += -march=mips64r6 -Wa,--trap cflags-$(CONFIG_CPU_R5000) += -march=r5000 -Wa,--trap cflags-$(CONFIG_CPU_R5432) += $(call cc-option,-march=r5400,-march=r5000) \