Re: [PATCH v2 1/4] meson: hide tsan related warnings

[Peter Maydell]

On Wed, 14 Aug 2024 at 23:42, Pierrick Bouvier
<pierrick.bouvier@linaro.org> wrote:
>
> When building with gcc-12 -fsanitize=thread, gcc reports some
> constructions not supported with tsan.
> Found on debian stable.
>
> qemu/include/qemu/atomic.h:36:52: error: ‘atomic_thread_fence’ is not 
> supported with ‘-fsanitize=thread’ [-Werror=tsan]
>    36 | #define smp_mb()                     ({ barrier(); 
> __atomic_thread_fence(__ATOMIC_SEQ_CST); })
>       |                                                    
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> Signed-off-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
> ---
>  meson.build | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/meson.build b/meson.build
> index 81ecd4bae7c..52e5aa95cc0 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -499,7 +499,15 @@ if get_option('tsan')
>                           prefix: '#include <sanitizer/tsan_interface.h>')
>      error('Cannot enable TSAN due to missing fiber annotation interface')
>    endif
> -  qemu_cflags = ['-fsanitize=thread'] + qemu_cflags
> +  tsan_warn_suppress = []
> +  # gcc (>=11) will report constructions not supported by tsan:
> +  # "error: ‘atomic_thread_fence’ is not supported with ‘-fsanitize=thread’"
> +  # https://gcc.gnu.org/gcc-11/changes.html
> +  # However, clang does not support this warning and this triggers an error.
> +  if cc.has_argument('-Wno-tsan')
> +    tsan_warn_suppress = ['-Wno-tsan']
> +  endif

That last part sounds like a clang bug -- -Wno-foo is supposed
to not be an error on compilers that don't implement -Wfoo for
any value of foo (unless some other warning/error would also
be emitted). At any rate, that's how gcc does it
(see the paragraph "When an unrecognized warning option ..."
in https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html )
and I thought clang did too...

thanks
-- PMM