diff options
| 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) | |
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) |