Re: [PATCH] qemu-thread: avoid false positive in pthread_cleanup_push

[Richard Henderson <richard.henderson@linaro.org>]

On 9/7/21 2:51 PM, Paolo Bonzini wrote:
> The following error occurs with GCC gcc (Debian 11-20210327-1) 11.0.1 20210327
> on Debian Bullseye:
> 
> ../util/qemu-thread-posix.c: In function ‘qemu_thread_start’:
> ../util/qemu-thread-posix.c:520:5: error: ‘__sigsetjmp’ accessing 200 bytes in a region of size 72 [-Werror=stringop-overflow=]
>    520 |     pthread_cleanup_push(qemu_thread_atexit_notify, NULL);
>        |     ^~~~~~~~~~~~~~~~~~~~
> ../util/qemu-thread-posix.c:520:5: note: referencing argument 1 of type ‘struct __jmp_buf_tag *’
> /usr/include/pthread.h:719:12: note: in a call to function ‘__sigsetjmp’
>    719 | extern int __sigsetjmp (struct __jmp_buf_tag *__env, int __savemask) __THROWNL;
>        |            ^~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> Disable the warning just like it was done in glibc.
> 
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/400
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>   util/qemu-thread-posix.c | 9 +++++++++
>   1 file changed, 9 insertions(+)
> 
> diff --git a/util/qemu-thread-posix.c b/util/qemu-thread-posix.c
> index fd9d714038..4cf47b3414 100644
> --- a/util/qemu-thread-posix.c
> +++ b/util/qemu-thread-posix.c
> @@ -537,7 +537,16 @@ 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);
> +
> +    /*
> +     * Work around GCC 11 false positives.  Ideally glibc would use
> +     * _Pragma itself, for now do it.  See
> +     * https://sourceware.org/bugzilla/show_bug.cgi?id=26647
> +     */
> +#pragma GCC diagnostic push
> +#pragma GCC diagnostic ignored "-Wstringop-overflow"
>       pthread_cleanup_push(qemu_thread_atexit_notify, NULL);
> +#pragma GCC diagnostic pop

I had a patch for this that didn't quite get applied for 6.1.
You can't leave the pragma unprotected for clang, unfortunately.

https://patchew.org/QEMU/20210803211907.150525-1-richard.henderson@linaro.org/

r~