[v2] meson: Avoid implicit declaration of functions

Commit Message

Michal Privoznik May 29, 2023, 2:12 p.m. UTC

While detecting a presence of a function via 'cc.links()'
gives desired result (i.e. detects whether function is present),
it also produces a warning on systems where the function is not
present (into meson-log.txt), e.g.:

  qemu.git/build/meson-private/tmph74x3p38/testfile.c:2:34: \
  warning: implicit declaration of function 'malloc_trim' [-Wimplicit-function-declaration]

We can check whether given function exists via
'cc.has_function()' or whether STATX_* macros exist via
'cc.has_header_symbol()'.

Resolves: https://bugs.gentoo.org/898810
Signed-off-by: Michal Privoznik <[e-mail]>
---

v2 of:

https://lists.gnu.org/archive/html/qemu-devel/2023-05/msg07138.html

Comments

Peter Maydell May 30, 2023, 9:30 a.m. UTC | #1

On Mon, 29 May 2023 at 15:13, Michal Privoznik <[e-mail]> wrote:
>
> While detecting a presence of a function via 'cc.links()'
> gives desired result (i.e. detects whether function is present),
> it also produces a warning on systems where the function is not
> present (into meson-log.txt), e.g.:
>
>   qemu.git/build/meson-private/tmph74x3p38/testfile.c:2:34: \
>   warning: implicit declaration of function 'malloc_trim' [-Wimplicit-function-declaration]

You should say why this matters, because in general warnings
in meson-log.txt are normal and expected. The only reason
we care about these particular warnings is because some
downstream distros are parsing logs for 'implicit declaration
of function' warnings as part of the "modern C" transition.

thanks
-- PMM

Patch

diff to v1:
- Drop cc.links() as it's redundant

 meson.build | 26 +++++---------------------
 1 file changed, 5 insertions(+), 21 deletions(-)

diff --git a/meson.build b/meson.build
index 2d48aa1e2e..21061b19d4 100644
--- a/meson.build
+++ b/meson.build
@@ -1797,8 +1797,7 @@  malloc = []
 if get_option('malloc') == 'system'
   has_malloc_trim = \
     get_option('malloc_trim').allowed() and \
-    cc.links('''#include <malloc.h>
-                int main(void) { malloc_trim(0); return 0; }''')
+    cc.has_function('malloc_trim', prefix: '#include <malloc.h>')
 else
   has_malloc_trim = false
   malloc = cc.find_library(get_option('malloc'), required: true)
@@ -1811,34 +1810,19 @@  if not has_malloc_trim and get_option('malloc_trim').enabled()
   endif
 endif
 
-# Check whether the glibc provides statx()
-
 gnu_source_prefix = '''
   #ifndef _GNU_SOURCE
   #define _GNU_SOURCE
   #endif
 '''
-statx_test = gnu_source_prefix + '''
-  #include <sys/stat.h>
-  int main(void) {
-    struct statx statxbuf;
-    statx(0, "", 0, STATX_BASIC_STATS, &statxbuf);
-    return 0;
-  }'''
 
-has_statx = cc.links(statx_test)
+# Check whether the glibc provides STATX_BASIC_STATS
+
+has_statx = cc.has_header_symbol('sys/stat.h', 'STATX_BASIC_STATS', prefix: gnu_source_prefix)
 
 # Check whether statx() provides mount ID information
 
-statx_mnt_id_test = gnu_source_prefix + '''
-  #include <sys/stat.h>
-  int main(void) {
-    struct statx statxbuf;
-    statx(0, "", 0, STATX_BASIC_STATS | STATX_MNT_ID, &statxbuf);
-    return statxbuf.stx_mnt_id;
-  }'''
-
-has_statx_mnt_id = cc.links(statx_mnt_id_test)
+has_statx_mnt_id = cc.has_header_symbol('sys/stat.h', 'STATX_MNT_ID', prefix: gnu_source_prefix)
 
 have_vhost_user_blk_server = get_option('vhost_user_blk_server') \
   .require(targetos == 'linux',