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| author | Will Deacon <will@kernel.org> | 2019-08-29 14:34:42 +0100 |
|---|---|---|
| committer | Will Deacon <will@kernel.org> | 2019-08-30 11:18:40 +0100 |
| commit | 03adcbd996be7ce81cac793b1511406a7a4df117 (patch) | |
| tree | 47a2847b763aad328f42f7cbc22984a129a47227 /arch/arm64/Makefile | |
| parent | 5aad6cdabbf91fd330bd216fe3c93d90f78bc7e7 (diff) | |
| download | linux-03adcbd996be7ce81cac793b1511406a7a4df117.tar.gz | |
arm64: atomics: Use K constraint when toolchain appears to support it
The 'K' constraint is a documented AArch64 machine constraint supported by GCC for matching integer constants that can be used with a 32-bit logical instruction. Unfortunately, some released compilers erroneously accept the immediate '4294967295' for this constraint, which is later refused by GAS at assembly time. This had led us to avoid the use of the 'K' constraint altogether. Instead, detect whether the compiler is up to the job when building the kernel and pass the 'K' constraint to our 32-bit atomic macros when it appears to be supported. Signed-off-by: Will Deacon <will@kernel.org>
Diffstat (limited to 'arch/arm64/Makefile')
| -rw-r--r-- | arch/arm64/Makefile | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/arch/arm64/Makefile b/arch/arm64/Makefile index 61de992bbea3..0cef056b5fb1 100644 --- a/arch/arm64/Makefile +++ b/arch/arm64/Makefile @@ -39,6 +39,12 @@ $(warning LSE atomics not supported by binutils) endif endif +cc_has_k_constraint := $(call try-run,echo \ + 'int main(void) { \ + asm volatile("and w0, w0, %w0" :: "K" (4294967295)); \ + return 0; \ + }' | $(CC) -S -x c -o "$$TMP" -,,-DCONFIG_CC_HAS_K_CONSTRAINT=1) + ifeq ($(CONFIG_ARM64), y) brokengasinst := $(call as-instr,1:\n.inst 0\n.rept . - 1b\n\nnop\n.endr\n,,-DCONFIG_BROKEN_GAS_INST=1) @@ -63,7 +69,8 @@ ifeq ($(CONFIG_GENERIC_COMPAT_VDSO), y) endif endif -KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst) $(compat_vdso) +KBUILD_CFLAGS += -mgeneral-regs-only $(lseinstr) $(brokengasinst) \ + $(compat_vdso) $(cc_has_k_constraint) KBUILD_CFLAGS += -fno-asynchronous-unwind-tables KBUILD_CFLAGS += $(call cc-disable-warning, psabi) KBUILD_AFLAGS += $(lseinstr) $(brokengasinst) $(compat_vdso) |