Re: [PATCH v5 10/10] arm64: atomics: Use K constraint when toolchain appears to support it
From: Andrew Murray <hidden>
Date: 2019-08-29 23:49:29
On Thu, Aug 29, 2019 at 04:48:34PM +0100, Will Deacon wrote:
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>
See my comments within this email thread, but for this patch as it is: Reviewed-by: Andrew Murray <redacted>
quoted hunk ↗ jump to hunk
--- arch/arm64/Makefile | 9 ++++++- arch/arm64/include/asm/atomic_ll_sc.h | 47 +++++++++++++++++++++++------------ 2 files changed, 39 insertions(+), 17 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)diff --git a/arch/arm64/include/asm/atomic_ll_sc.h b/arch/arm64/include/asm/atomic_ll_sc.h index 95091f72228b..7fa042f5444e 100644 --- a/arch/arm64/include/asm/atomic_ll_sc.h +++ b/arch/arm64/include/asm/atomic_ll_sc.h@@ -23,6 +23,10 @@ asm_ops "\n" \ #define __LL_SC_FALLBACK(asm_ops) asm_ops #endif +#ifndef CONFIG_CC_HAS_K_CONSTRAINT +#define K +#endif + /* * AArch64 UP and SMP safe atomic ops. We use load exclusive and * store exclusive to ensure that these are atomic. We may loop@@ -113,10 +117,15 @@ ATOMIC_OPS(sub, sub, J) ATOMIC_FETCH_OP (_acquire, , a, , "memory", __VA_ARGS__)\ ATOMIC_FETCH_OP (_release, , , l, "memory", __VA_ARGS__) -ATOMIC_OPS(and, and, ) +ATOMIC_OPS(and, and, K) +ATOMIC_OPS(or, orr, K) +ATOMIC_OPS(xor, eor, K) +/* + * GAS converts the mysterious and undocumented BIC (immediate) alias to + * an AND (immediate) instruction with the immediate inverted. We don't + * have a constraint for this, so fall back to register. + */ ATOMIC_OPS(andnot, bic, ) -ATOMIC_OPS(or, orr, ) -ATOMIC_OPS(xor, eor, ) #undef ATOMIC_OPS #undef ATOMIC_FETCH_OP@@ -208,9 +217,14 @@ ATOMIC64_OPS(sub, sub, J) ATOMIC64_FETCH_OP (_release,, , l, "memory", __VA_ARGS__) ATOMIC64_OPS(and, and, L) -ATOMIC64_OPS(andnot, bic, ) ATOMIC64_OPS(or, orr, L) ATOMIC64_OPS(xor, eor, L) +/* + * GAS converts the mysterious and undocumented BIC (immediate) alias to + * an AND (immediate) instruction with the immediate inverted. We don't + * have a constraint for this, so fall back to register. + */ +ATOMIC64_OPS(andnot, bic, ) #undef ATOMIC64_OPS #undef ATOMIC64_FETCH_OP@@ -280,21 +294,21 @@ __ll_sc__cmpxchg_case_##name##sz(volatile void *ptr, \ * handle the 'K' constraint for the value 4294967295 - thus we use no * constraint for 32 bit operations. */ -__CMPXCHG_CASE(w, b, , 8, , , , , ) -__CMPXCHG_CASE(w, h, , 16, , , , , ) -__CMPXCHG_CASE(w, , , 32, , , , , ) +__CMPXCHG_CASE(w, b, , 8, , , , , K) +__CMPXCHG_CASE(w, h, , 16, , , , , K) +__CMPXCHG_CASE(w, , , 32, , , , , K) __CMPXCHG_CASE( , , , 64, , , , , L) -__CMPXCHG_CASE(w, b, acq_, 8, , a, , "memory", ) -__CMPXCHG_CASE(w, h, acq_, 16, , a, , "memory", ) -__CMPXCHG_CASE(w, , acq_, 32, , a, , "memory", ) +__CMPXCHG_CASE(w, b, acq_, 8, , a, , "memory", K) +__CMPXCHG_CASE(w, h, acq_, 16, , a, , "memory", K) +__CMPXCHG_CASE(w, , acq_, 32, , a, , "memory", K) __CMPXCHG_CASE( , , acq_, 64, , a, , "memory", L) -__CMPXCHG_CASE(w, b, rel_, 8, , , l, "memory", ) -__CMPXCHG_CASE(w, h, rel_, 16, , , l, "memory", ) -__CMPXCHG_CASE(w, , rel_, 32, , , l, "memory", ) +__CMPXCHG_CASE(w, b, rel_, 8, , , l, "memory", K) +__CMPXCHG_CASE(w, h, rel_, 16, , , l, "memory", K) +__CMPXCHG_CASE(w, , rel_, 32, , , l, "memory", K) __CMPXCHG_CASE( , , rel_, 64, , , l, "memory", L) -__CMPXCHG_CASE(w, b, mb_, 8, dmb ish, , l, "memory", ) -__CMPXCHG_CASE(w, h, mb_, 16, dmb ish, , l, "memory", ) -__CMPXCHG_CASE(w, , mb_, 32, dmb ish, , l, "memory", ) +__CMPXCHG_CASE(w, b, mb_, 8, dmb ish, , l, "memory", K) +__CMPXCHG_CASE(w, h, mb_, 16, dmb ish, , l, "memory", K) +__CMPXCHG_CASE(w, , mb_, 32, dmb ish, , l, "memory", K) __CMPXCHG_CASE( , , mb_, 64, dmb ish, , l, "memory", L) #undef __CMPXCHG_CASE@@ -332,5 +346,6 @@ __CMPXCHG_DBL( , , , ) __CMPXCHG_DBL(_mb, dmb ish, l, "memory") #undef __CMPXCHG_DBL +#undef K #endif /* __ASM_ATOMIC_LL_SC_H */-- 2.11.0
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