Re: [PATCH] riscv: cmpxchg: Use .option arch for Zacas and Zabha

[Jesse Taube]

On Fri, Jul 17, 2026 at 11:49 AM Vivian Wang <wangruikang@xxxxxxxxxxx> wrote:
>
> Instead of adding these to -march globally, use .option arch to use
> instructions from these extensions only in code paths where we know they
> are available, like how it is done for most other extensions.
> TOOLCHAIN_HAS_{ZACAS,ZABHA} already depend on AS_HAS_OPTION_ARCH, so
> this is not a functionality regression even on older assemblers.
>
> Although the compiler is unlikely to generate atomics on its own accord,
> this aligns handling of Zacas and Zabha with most other extensions and
> improves consistency on how assembly code requiring extra extensions is
> written in kernel code.
>
> This is analogous to the use of __LSE_PREAMBLE or .arch_extension lse in
> arm64 code.
>
> Signed-off-by: Vivian Wang <wangruikang@xxxxxxxxxxx>

Reviewed-by: Jesse Taube <jtaubepe@xxxxxxxxxx>

> ---
>  arch/riscv/Makefile              |  6 ------
>  arch/riscv/include/asm/cmpxchg.h | 14 +++++++++++++-
>  2 files changed, 13 insertions(+), 7 deletions(-)
>
> diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
> index ce0cc737f870..4d74b141122c 100644
> --- a/arch/riscv/Makefile
> +++ b/arch/riscv/Makefile
> @@ -75,12 +75,6 @@ else
>  riscv-march-$(CONFIG_TOOLCHAIN_NEEDS_EXPLICIT_ZICSR_ZIFENCEI) := $(riscv-march-y)_zicsr_zifencei
>  endif
>
> -# Check if the toolchain supports Zacas
> -riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZACAS) := $(riscv-march-y)_zacas
> -
> -# Check if the toolchain supports Zabha
> -riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZABHA) := $(riscv-march-y)_zabha
> -
>  KBUILD_BASE_ISA = -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)fd([^v_]*)v?/\1\2/')
>  export KBUILD_BASE_ISA
>
> diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
> index 8712cf9c69dc..662e160b0522 100644
> --- a/arch/riscv/include/asm/cmpxchg.h
> +++ b/arch/riscv/include/asm/cmpxchg.h
> @@ -23,7 +23,10 @@
>             riscv_has_extension_unlikely(RISCV_ISA_EXT_ZABHA)) {                \
>                 __asm__ __volatile__ (                                          \
>                         prepend                                                 \
> +                       "       .option push\n"                                 \
> +                       "       .option arch, +zabha\n"                         \
>                         "       amoswap" swap_sfx " %0, %z2, %1\n"              \
> +                       "       .option pop\n"                                  \
>                         swap_append                                             \
>                         : "=&r" (r), "+A" (*(p))                                \
>                         : "rJ" (n)                                              \
> @@ -141,7 +144,10 @@
>                                                                                 \
>                 __asm__ __volatile__ (                                          \
>                         cas_prepend                                                     \
> +                       "       .option push\n"                                 \
> +                       "       .option arch, +zacas, +zabha\n"                         \
>                         "       amocas" cas_sfx " %0, %z2, %1\n"                \
> +                       "       .option pop\n"                                  \
>                         cas_append                                                      \
>                         : "+&r" (r), "+A" (*(p))                                \
>                         : "rJ" (n)                                              \
> @@ -188,7 +194,10 @@
>                                                                         \
>                 __asm__ __volatile__ (                                  \
>                         cas_prepend                                     \
> +                       "       .option push\n"                         \
> +                       "       .option arch, +zacas\n"                 \
>                         "       amocas" cas_sfx " %0, %z2, %1\n"        \
> +                       "       .option pop\n"                          \
>                         cas_append                                      \
>                         : "+&r" (r), "+A" (*(p))                        \
>                         : "rJ" (n)                                      \
> @@ -340,7 +349,10 @@ union __u128_halves {
>         register unsigned long t4 asm ("t4") = __ho.high;                       \
>                                                                                 \
>         __asm__ __volatile__ (                                                  \
> -                "       amocas.q" cas_sfx " %0, %z3, %2"                       \
> +                "       .option push\n"                                        \
> +                "       .option arch, +zacas\n"                                \
> +                "       amocas.q" cas_sfx " %0, %z3, %2\n"                     \
> +                "       .option pop\n"                                         \
>                  : "+&r" (t3), "+&r" (t4), "+A" (*(p))                          \
>                  : "rJ" (t1), "rJ" (t2)                                         \
>                  : "memory");                                                   \
>
> ---
> base-commit: dc59e4fea9d83f03bad6bddf3fa2e52491777482
> change-id: 20260717-riscv-no-zacas-zabha-in-march-28e278a993a2
>
> Best regards,
> --
> Vivian Wang <wangruikang@xxxxxxxxxxx>
>
>
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