Re: [PATCH] perf bench futex: Define SYS_futex on 32-bit arches with 64-bit time_t

[Ian Rogers]

On Wed, Sep 2, 2026 at 2:32 AM Nylon Chen <nylon.chen@xxxxxxxxxx> wrote:
>
> The kernel does not provide sys_futex() on 32-bit architectures that lack
> a 32-bit time representation, such as riscv32. Consequently glibc does not
> define SYS_futex there, only SYS_futex_time64, and perf bench's futex
> benchmarks fail to build:
>
>   bench/futex.h: In function 'futex_syscall':
>   bench/futex.h:77:18: error: 'SYS_futex' undeclared (first use in this function)
>
> Define SYS_futex as SYS_futex_time64 when only the latter is available.
> The guard and its comment are taken verbatim from
> tools/testing/selftests/futex/include/futextest.h, where they were added by
> commit 04850819c65c ("selftests/futex: Define SYS_futex on 32-bit
> architectures with 64-bit time_t"), keeping the two futex userspace headers
> in sync.
>
> No timespec conversion helper is needed on top of this. glibc lays out
> struct timespec on 32-bit architectures with 64-bit time_t as
> { int64 tv_sec; int32 tv_nsec; 32-bit pad }, which is compatible with
> struct __kernel_timespec, and every futex_wait()/futex_lock_pi()/
> futex_wait_requeue_pi() call site in perf bench passes a NULL timeout
> anyway, so no timespec ever crosses the syscall boundary here.
>
> Note that an earlier and more ambitious attempt at this was
> commit c1ff12dac465 ("perf bench futex: Add support for 32-bit systems
> with 64-bit time_t"), reverted by
> commit ba4026b09d83 ("Revert "perf bench futex: Add support for 32-bit
> systems with 64-bit time_t"") because it included linux/time_types.h,
> which is unavailable on older distributions. This change deliberately
> avoids that dependency and adds only the one guard needed to fix
> compilation.
>
> Signed-off-by: Nylon Chen <nylon.chen@xxxxxxxxxx>

Reviewed-by: Ian Rogers <irogers@xxxxxxxxxx>

Thanks,
Ian

> ---
>  tools/perf/bench/futex.h | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/tools/perf/bench/futex.h b/tools/perf/bench/futex.h
> index fcb72d682cf8..6df8837b365b 100644
> --- a/tools/perf/bench/futex.h
> +++ b/tools/perf/bench/futex.h
> @@ -14,6 +14,17 @@
>  #include <sys/types.h>
>  #include <linux/futex.h>
>
> +/*
> + * SYS_futex is expected from system C library, in glibc some 32-bit
> + * architectures (e.g. RV32) are using 64-bit time_t, therefore it doesn't have
> + * SYS_futex defined but just SYS_futex_time64. Define SYS_futex as
> + * SYS_futex_time64 in this situation to ensure the compilation and the
> + * compatibility.
> + */
> +#if !defined(SYS_futex) && defined(SYS_futex_time64)
> +#define SYS_futex SYS_futex_time64
> +#endif
> +
>  struct bench_futex_parameters {
>         bool silent;
>         bool fshared;
>
> base-commit: 66498c75b4f8017f62d720d9b59675bdf3abce91
> --
> 2.43.7
>