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

Pierrick Bouvier
2024-08-15T17:43:32Z

On 8/15/24 04:05, Daniel P. Berrangé wrote:
> On Thu, Aug 15, 2024 at 11:12:39AM +0100, Peter Maydell wrote:
>> 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).
>
> -Wno-foo isn't an error, but it is a warning... which we then
> turn into an error due to -Werror, unless we pass -Wno-unknown-warning-option
> to clang.
>

Right, it's a consequence.

>> 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
>>
>
> With regards,
> Daniel