Re: [PATCH v3 01/66] util: Suppress -Wstringop-overflow in qemu_thread_start

[Peter Maydell]

On Wed, 18 Aug 2021 at 20:22, Richard Henderson
<richard.henderson@linaro.org> wrote:
>
> This seems to be either a glibc or gcc bug, but the code
> appears to be fine with the warning suppressed.
>
> Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
> ---
>  util/qemu-thread-posix.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> index fd9d714038..6c5004220d 100644
> --- a/util/qemu-thread-posix.c
> +++ b/util/qemu-thread-posix.c
> @@ -537,9 +537,28 @@ static void *qemu_thread_start(void *args)
>      QEMU_TSAN_ANNOTATE_THREAD_NAME(qemu_thread_args->name);
>      g_free(qemu_thread_args->name);
>      g_free(qemu_thread_args);
> +
> +    /*
> +     * GCC 11 with glibc 2.17 on PowerPC reports
> +     *
> +     * qemu-thread-posix.c:540:5: error: ‘__sigsetjmp’ accessing 656 bytes
> +     *   in a region of size 528 [-Werror=stringop-overflow=]
> +     * 540 |     pthread_cleanup_push(qemu_thread_atexit_notify, NULL);
> +     *     |     ^~~~~~~~~~~~~~~~~~~~
> +     *
> +     * which is clearly nonsense.
> +     */
> +#pragma GCC diagnostic push
> +#ifndef __clang__
> +#pragma GCC diagnostic ignored "-Wstringop-overflow"
> +#endif
> +
>      pthread_cleanup_push(qemu_thread_atexit_notify, NULL);

Fixed in glibc in commit
https://sourceware.org/git/?p=glibc.git;a=commit;h=548f467fa14ffe7d955beeb31b30e2aeae4467e0

I think.

I found this mailing list thread:
https://www.mail-archive.com/dm-devel@redhat.com/msg20144.html

which suggests that another workaround would be to include pthread.h
before setjmp.h. For us that would mean we'd have to pull
pthread.h in in osdep.h, though...

>      r = start_routine(arg);
>      pthread_cleanup_pop(1);
> +
> +#pragma GCC diagnostic pop
> +
>      return r;
>  }

With a link to the glibc commit in the comment,
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>

thanks
-- PMM