Re: [PATCH] LoongArch: Only use SC.Q when supported by the assembler

[Hengqi Chen]

On Wed, Feb 25, 2026 at 6:09 PM Thomas Weißschuh
<thomas.weissschuh@xxxxxxxxxxxxx> wrote:
>
> The 128-bit atomic cmpxchg implementation uses the SC.Q instruction.
> Older versions of GNU AS do not support that instruction, erroring out:
>
> ERROR:root:{standard input}: Assembler messages:
> {standard input}:4831: Error: no match insn: sc.q       $t0,$t1,$r14
> {standard input}:6407: Error: no match insn: sc.q       $t0,$t1,$r23
> {standard input}:10856: Error: no match insn: sc.q      $t0,$t1,$r14
> make[4]: *** [../scripts/Makefile.build:289: mm/slub.o] Error 1
>
> (Binutils 2.41)
>
> Test support for SC.Q in kconfig and disable the atomics if the
> instruction is not available.
>
> Fixes: f0e4b1b6e295 ("LoongArch: Add 128-bit atomic cmpxchg support")
> Closes: https://lore.kernel.org/lkml/20260216082834-edc51c46-7b7a-4295-8ea5-4d9a3ca2224f@xxxxxxxxxxxxx/
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
> ---

Acked-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>
Tested-by: Hengqi Chen <hengqi.chen@xxxxxxxxx>

>  arch/loongarch/Kconfig               | 3 +++
>  arch/loongarch/include/asm/cmpxchg.h | 5 +++++
>  2 files changed, 8 insertions(+)
>
> diff --git a/arch/loongarch/Kconfig b/arch/loongarch/Kconfig
> index d211c6572b0a..92068ff38685 100644
> --- a/arch/loongarch/Kconfig
> +++ b/arch/loongarch/Kconfig
> @@ -304,6 +304,9 @@ config AS_HAS_LBT_EXTENSION
>  config AS_HAS_LVZ_EXTENSION
>         def_bool $(as-instr,hvcl 0)
>
> +config AS_HAS_SCQ_EXTENSION
> +       def_bool $(as-instr,sc.q \$t0$(comma)\$t1$(comma)\$t2)
> +
>  config CC_HAS_ANNOTATE_TABLEJUMP
>         def_bool $(cc-option,-mannotate-tablejump)
>
> diff --git a/arch/loongarch/include/asm/cmpxchg.h b/arch/loongarch/include/asm/cmpxchg.h
> index 58cabab6d90d..909f9274fe71 100644
> --- a/arch/loongarch/include/asm/cmpxchg.h
> +++ b/arch/loongarch/include/asm/cmpxchg.h
> @@ -238,6 +238,8 @@ __cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, unsigned int
>         arch_cmpxchg((ptr), (o), (n));                                  \
>    })
>
> +#ifdef CONFIG_AS_HAS_SCQ_EXTENSION
> +
>  union __u128_halves {
>         u128 full;
>         struct {
> @@ -290,6 +292,9 @@ union __u128_halves {
>         BUILD_BUG_ON(sizeof(*(ptr)) != 16);                             \
>         __arch_cmpxchg128(ptr, o, n, "");                               \
>  })
> +
> +#endif /* CONFIG_AS_HAS_SCQ_EXTENSION */
> +
>  #else
>  #include <asm-generic/cmpxchg-local.h>
>  #define arch_cmpxchg64_local(ptr, o, n) __generic_cmpxchg64_local((ptr), (o), (n))
>
> ---
> base-commit: 2961f841b025fb234860bac26dfb7fa7cb0fb122
> change-id: 20260218-loongarch-scq-2434ec5aec4d
>
> Best regards,
> --
> Thomas Weißschuh <thomas.weissschuh@xxxxxxxxxxxxx>
>