Re: [PATCH v3 1/7] meson: Run some compiler checks using -Wno-unused-value

[Philippe Mathieu-Daudé]

On 19/12/24 01:37, Nicholas Piggin wrote:
> On Thu Dec 19, 2024 at 4:21 AM AEST, Philippe Mathieu-Daudé wrote:
> > When running Clang static analyzer on macOS I'm getting:
> >
> >    include/qemu/osdep.h:634:8: error: redefinition of 'iovec'
> >      634 | struct iovec {
> >          |        ^
> >    
> > /Library/Developer/CommandLineTools/SDKs/MacOSX.sdk/usr/include/sys/_types/_iovec_t.h:31:8:
> >  note: previous definition is here
> >       31 | struct iovec {
> >          |        ^
> >    1 error generated.
> >
> > Looking at meson-logs.txt, the analyzer enables -Wunused-value
> > making meson generated code to fail:
> >
> >      Code:
> >      #include <sys/uio.h>
> >              void bar(void) {
> >                  sizeof(struct iovec);
> >              }
> >      -----------
> >      stderr:
> >      meson-private/tmpe8_1b_00/testfile.c:3:13: error: expression result unused 
> > [-Werror,-Wunused-value]
> >          3 |             sizeof(struct iovec);
> >            |             ^~~~~~~~~~~~~~~~~~~~
> >      1 error generated.
> >      -----------
> >      Checking for type "struct iovec" : NO
> >
> >      Code:
> >      #include <utmpx.h>
> >              void bar(void) {
> >                  sizeof(struct utmpx);
> >              }
> >      -----------
> >      stderr:
> >      meson-private/tmp3n0u490p/testfile.c:3:13: error: expression result unused 
> > [-Werror,-Wunused-value]
> >          3 |             sizeof(struct utmpx);
> >            |             ^~~~~~~~~~~~~~~~~~~~
> >      1 error generated.
> >      -----------
> >      Checking for type "struct utmpx" : NO
> >
> >      Code:
> >
> >              #include <getopt.h>
> >              int main(void) {
> >                  /* If it's not defined as a macro, try to use as a symbol */
> >                  #ifndef optreset
> >                      optreset;
> >                  #endif
> >                  return 0;
> >              }
> >      -----------
> >      stderr:
> >      meson-private/tmp1rzob_os/testfile.c:6:17: error: expression result unused 
> > [-Werror,-Wunused-value]
> >          6 |                 optreset;
> >            |                 ^~~~~~~~
> >      1 error generated.
> >      -----------
> >      Header "getopt.h" has symbol "optreset" : NO
> >
> >      Code:
> >
> >              #include <vmnet/vmnet.h>
> >              int main(void) {
> >                  /* If it's not defined as a macro, try to use as a symbol */
> >                  #ifndef VMNET_BRIDGED_MODE
> >                      VMNET_BRIDGED_MODE;
> >                  #endif
> >                  return 0;
> >              }
> >      -----------
> >      stderr:
> >      meson-private/tmpl9jgsxpt/testfile.c:6:17: error: expression result unused 
> > [-Werror,-Wunused-value]
> >          6 |                 VMNET_BRIDGED_MODE;
> >            |                 ^~~~~~~~~~~~~~~~~~
> >      1 error generated.
> >      -----------
> >      Header "vmnet/vmnet.h" has symbol "VMNET_BRIDGED_MODE" with dependency 
> > appleframeworks: NO
> >      ../meson.build:1174: WARNING: vmnet.framework API is outdated, disabling
> >
> > Fix by explicitly disabling -Wunused-value from these meson checks.
> >
> > Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
> > ---
> > RFC: Probably meson should do that in has_header_symbol() / has_type()?
>
> I don't know about the build system to answer this, but should we
> instead disable -Werror on these tests to be a bit more future-proof?
> Compilers often add new warnings or catch more cases of existing
> warnings.

Sorry, I didn't mean to include this patch in this series. I happen
to have my series on top of it and forgot to change the base commit.

> Alternative would be to keep -Werror but fail the build if a test
> throws a warning, but that seems like a lot more work for little
> benefit...

I'm trying to fix it on the meson side with this:

-- >8 --
diff --git a/mesonbuild/compilers/mixins/clike.py 
b/mesonbuild/compilers/mixins/clike.py
index d56547b47..9d6957973 100644
--- a/mesonbuild/compilers/mixins/clike.py
+++ b/mesonbuild/compilers/mixins/clike.py
@@ -360,7 +360,7 @@ class CLikeCompiler(Compiler):
         int main(void) {{
             /* If it's not defined as a macro, try to use as a symbol */
             #ifndef {symbol}
-                {symbol};
+            (void) {symbol};
             #endif
             return 0;
         }}'''
@@ -885,7 +885,8 @@ class CLikeCompiler(Compiler):
                  dependencies: T.Optional[T.List['Dependency']] = 
None) -> T.Tuple[bool, bool]:
         t = f'''{prefix}
         void bar(void) {{
-            (void) sizeof({typename});
+            size_t foo = sizeof({typename});
+            (void) foo;
         }}'''
         return self.compiles(t, env, extra_args=extra_args,
                              dependencies=dependencies)
---