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SubjectRe: [PATCH v2] arm64: lse: fix LSE atomics with LLVM's integrated assembler
On Tue, Oct 8, 2019 at 2:27 PM 'Sami Tolvanen' via Clang Built Linux
<clang-built-linux@googlegroups.com> wrote:
>
> Unlike gcc, clang considers each inline assembly block to be independent
> and therefore, when using the integrated assembler for inline assembly,
> any preambles that enable features must be repeated in each block.
>
> This change defines __LSE_PREAMBLE and adds it to each inline assembly
> block that has LSE instructions, which allows them to be compiled also
> with clang's assembler.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/671
> Signed-off-by: Sami Tolvanen <samitolvanen@google.com>


Thanks, I think this will better limit the assembler to use of these
instructions, while preventing the C compiler from emitting them.
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang AS=clang -j71 clean
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang AS=clang
-j71 defconfig
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang AS=clang
-j71 fs/ext4/balloc.o
<error explosion>
$ git am <patch.eml>
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang AS=clang
-j71 fs/ext4/balloc.o
...
$ echo $?
0
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang AS=clang -j71 clean
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang -j71 defconfig
$ ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- make CC=clang -j71
<builds successfully>
$ qemu-system-aarch64 -kernel arch/arm64/boot/Image.gz -machine virt
-cpu cortex-a72 -nographic --append "console=ttyAMA0" -m 2048 -initrd
/android1/buildroot/output/images/rootfs.cpio
<boots successfully; doesn't appear to regress the case of GAS, though
I doubt such a compiler directive would>

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
> v2:
> - Add a preamble to inline assembly blocks that use LSE instead
> of allowing the compiler to emit LSE instructions everywhere.
>
> ---
> arch/arm64/include/asm/atomic_lse.h | 19 +++++++++++++++++++
> arch/arm64/include/asm/lse.h | 6 +++---
> 2 files changed, 22 insertions(+), 3 deletions(-)
>
> diff --git a/arch/arm64/include/asm/atomic_lse.h b/arch/arm64/include/asm/atomic_lse.h
> index c6bd87d2915b..3ee600043042 100644
> --- a/arch/arm64/include/asm/atomic_lse.h
> +++ b/arch/arm64/include/asm/atomic_lse.h
> @@ -14,6 +14,7 @@
> static inline void __lse_atomic_##op(int i, atomic_t *v) \
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " " #asm_op " %w[i], %[v]\n" \
> : [i] "+r" (i), [v] "+Q" (v->counter) \
> : "r" (v)); \
> @@ -30,6 +31,7 @@ ATOMIC_OP(add, stadd)
> static inline int __lse_atomic_fetch_##op##name(int i, atomic_t *v) \
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " " #asm_op #mb " %w[i], %w[i], %[v]" \
> : [i] "+r" (i), [v] "+Q" (v->counter) \
> : "r" (v) \
> @@ -58,6 +60,7 @@ static inline int __lse_atomic_add_return##name(int i, atomic_t *v) \
> u32 tmp; \
> \
> asm volatile( \
> + __LSE_PREAMBLE \
> " ldadd" #mb " %w[i], %w[tmp], %[v]\n" \
> " add %w[i], %w[i], %w[tmp]" \
> : [i] "+r" (i), [v] "+Q" (v->counter), [tmp] "=&r" (tmp) \
> @@ -77,6 +80,7 @@ ATOMIC_OP_ADD_RETURN( , al, "memory")
> static inline void __lse_atomic_and(int i, atomic_t *v)
> {
> asm volatile(
> + __LSE_PREAMBLE
> " mvn %w[i], %w[i]\n"
> " stclr %w[i], %[v]"
> : [i] "+&r" (i), [v] "+Q" (v->counter)
> @@ -87,6 +91,7 @@ static inline void __lse_atomic_and(int i, atomic_t *v)
> static inline int __lse_atomic_fetch_and##name(int i, atomic_t *v) \
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " mvn %w[i], %w[i]\n" \
> " ldclr" #mb " %w[i], %w[i], %[v]" \
> : [i] "+&r" (i), [v] "+Q" (v->counter) \
> @@ -106,6 +111,7 @@ ATOMIC_FETCH_OP_AND( , al, "memory")
> static inline void __lse_atomic_sub(int i, atomic_t *v)
> {
> asm volatile(
> + __LSE_PREAMBLE
> " neg %w[i], %w[i]\n"
> " stadd %w[i], %[v]"
> : [i] "+&r" (i), [v] "+Q" (v->counter)
> @@ -118,6 +124,7 @@ static inline int __lse_atomic_sub_return##name(int i, atomic_t *v) \
> u32 tmp; \
> \
> asm volatile( \
> + __LSE_PREAMBLE \
> " neg %w[i], %w[i]\n" \
> " ldadd" #mb " %w[i], %w[tmp], %[v]\n" \
> " add %w[i], %w[i], %w[tmp]" \
> @@ -139,6 +146,7 @@ ATOMIC_OP_SUB_RETURN( , al, "memory")
> static inline int __lse_atomic_fetch_sub##name(int i, atomic_t *v) \
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " neg %w[i], %w[i]\n" \
> " ldadd" #mb " %w[i], %w[i], %[v]" \
> : [i] "+&r" (i), [v] "+Q" (v->counter) \
> @@ -159,6 +167,7 @@ ATOMIC_FETCH_OP_SUB( , al, "memory")
> static inline void __lse_atomic64_##op(s64 i, atomic64_t *v) \
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " " #asm_op " %[i], %[v]\n" \
> : [i] "+r" (i), [v] "+Q" (v->counter) \
> : "r" (v)); \
> @@ -175,6 +184,7 @@ ATOMIC64_OP(add, stadd)
> static inline long __lse_atomic64_fetch_##op##name(s64 i, atomic64_t *v)\
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " " #asm_op #mb " %[i], %[i], %[v]" \
> : [i] "+r" (i), [v] "+Q" (v->counter) \
> : "r" (v) \
> @@ -203,6 +213,7 @@ static inline long __lse_atomic64_add_return##name(s64 i, atomic64_t *v)\
> unsigned long tmp; \
> \
> asm volatile( \
> + __LSE_PREAMBLE \
> " ldadd" #mb " %[i], %x[tmp], %[v]\n" \
> " add %[i], %[i], %x[tmp]" \
> : [i] "+r" (i), [v] "+Q" (v->counter), [tmp] "=&r" (tmp) \
> @@ -222,6 +233,7 @@ ATOMIC64_OP_ADD_RETURN( , al, "memory")
> static inline void __lse_atomic64_and(s64 i, atomic64_t *v)
> {
> asm volatile(
> + __LSE_PREAMBLE
> " mvn %[i], %[i]\n"
> " stclr %[i], %[v]"
> : [i] "+&r" (i), [v] "+Q" (v->counter)
> @@ -232,6 +244,7 @@ static inline void __lse_atomic64_and(s64 i, atomic64_t *v)
> static inline long __lse_atomic64_fetch_and##name(s64 i, atomic64_t *v) \
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " mvn %[i], %[i]\n" \
> " ldclr" #mb " %[i], %[i], %[v]" \
> : [i] "+&r" (i), [v] "+Q" (v->counter) \
> @@ -251,6 +264,7 @@ ATOMIC64_FETCH_OP_AND( , al, "memory")
> static inline void __lse_atomic64_sub(s64 i, atomic64_t *v)
> {
> asm volatile(
> + __LSE_PREAMBLE
> " neg %[i], %[i]\n"
> " stadd %[i], %[v]"
> : [i] "+&r" (i), [v] "+Q" (v->counter)
> @@ -263,6 +277,7 @@ static inline long __lse_atomic64_sub_return##name(s64 i, atomic64_t *v) \
> unsigned long tmp; \
> \
> asm volatile( \
> + __LSE_PREAMBLE \
> " neg %[i], %[i]\n" \
> " ldadd" #mb " %[i], %x[tmp], %[v]\n" \
> " add %[i], %[i], %x[tmp]" \
> @@ -284,6 +299,7 @@ ATOMIC64_OP_SUB_RETURN( , al, "memory")
> static inline long __lse_atomic64_fetch_sub##name(s64 i, atomic64_t *v) \
> { \
> asm volatile( \
> + __LSE_PREAMBLE \
> " neg %[i], %[i]\n" \
> " ldadd" #mb " %[i], %[i], %[v]" \
> : [i] "+&r" (i), [v] "+Q" (v->counter) \
> @@ -305,6 +321,7 @@ static inline s64 __lse_atomic64_dec_if_positive(atomic64_t *v)
> unsigned long tmp;
>
> asm volatile(
> + __LSE_PREAMBLE
> "1: ldr %x[tmp], %[v]\n"
> " subs %[ret], %x[tmp], #1\n"
> " b.lt 2f\n"
> @@ -331,6 +348,7 @@ static inline u##sz __lse__cmpxchg_case_##name##sz(volatile void *ptr, \
> unsigned long tmp; \
> \
> asm volatile( \
> + __LSE_PREAMBLE \
> " mov %" #w "[tmp], %" #w "[old]\n" \
> " cas" #mb #sfx "\t%" #w "[tmp], %" #w "[new], %[v]\n" \
> " mov %" #w "[ret], %" #w "[tmp]" \
> @@ -377,6 +395,7 @@ static inline long __lse__cmpxchg_double##name(unsigned long old1, \
> register unsigned long x4 asm ("x4") = (unsigned long)ptr; \
> \
> asm volatile( \
> + __LSE_PREAMBLE \
> " casp" #mb "\t%[old1], %[old2], %[new1], %[new2], %[v]\n"\
> " eor %[old1], %[old1], %[oldval1]\n" \
> " eor %[old2], %[old2], %[oldval2]\n" \
> diff --git a/arch/arm64/include/asm/lse.h b/arch/arm64/include/asm/lse.h
> index 80b388278149..73834996c4b6 100644
> --- a/arch/arm64/include/asm/lse.h
> +++ b/arch/arm64/include/asm/lse.h
> @@ -6,6 +6,8 @@
>
> #if defined(CONFIG_AS_LSE) && defined(CONFIG_ARM64_LSE_ATOMICS)
>
> +#define __LSE_PREAMBLE ".arch armv8-a+lse\n"
> +
> #include <linux/compiler_types.h>
> #include <linux/export.h>
> #include <linux/jump_label.h>
> @@ -14,8 +16,6 @@
> #include <asm/atomic_lse.h>
> #include <asm/cpucaps.h>
>
> -__asm__(".arch_extension lse");
> -
> extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
> extern struct static_key_false arm64_const_caps_ready;
>
> @@ -34,7 +34,7 @@ static inline bool system_uses_lse_atomics(void)
>
> /* In-line patching at runtime */
> #define ARM64_LSE_ATOMIC_INSN(llsc, lse) \
> - ALTERNATIVE(llsc, lse, ARM64_HAS_LSE_ATOMICS)
> + ALTERNATIVE(llsc, __LSE_PREAMBLE lse, ARM64_HAS_LSE_ATOMICS)
>
> #else /* CONFIG_AS_LSE && CONFIG_ARM64_LSE_ATOMICS */
>
> --
> 2.23.0.581.g78d2f28ef7-goog
>
> --
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--
Thanks,
~Nick Desaulniers

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