On 15/08/2024 19.54, Peter Maydell wrote:
On Thu, 15 Aug 2024 at 12:05, Daniel P. Berrangé <berrange@xxxxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx>
---
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.
Which is irritating if you want to be able to blanket say
'-Wno-silly-compiler-warning' and not see any of that
warning regardless of compiler version. That's why the
gcc behaviour is the way it is (i.e. -Wno-such-thingy
is neither a warning nor an error if it would be the only
warning/error), and if clang doesn't match it that's a shame.
I thought that Clang would behave the same way as GCC, but apparently it
does not (anymore?):
$ gcc -Wno-flux-capacitors testprg.c -o testprg
$ clang -Wno-flux-capacitors testprg.c -o testprg
warning: unknown warning option '-Wno-flux-capacitors'
[-Wunknown-warning-option]
1 warning generated.
Thomas
