[PATCH v2 1/3] util/osdep: Avoid madvise proto on modern Solaris

[Andrew Deason]

On older Solaris releases, we didn't get a protype for madvise, and so
util/osdep.c provides its own prototype. Some time between the public
Solaris 11.4 release and Solaris 11.4.42 CBE, we started getting an
madvise prototype that looks like this:

    extern int madvise(void *, size_t, int);

which conflicts with the prototype in util/osdeps.c. Instead of always
declaring this prototype, check if we're missing the madvise()
prototype, and only declare it ourselves if the prototype is missing.

The 'missing_madvise_proto' meson check contains an obviously wrong
prototype for madvise. So if that code compiles and links, we must be
missing the actual prototype for madvise.

Signed-off-by: Andrew Deason <adeason@sinenomine.net>
---
To be clear, I'm okay with removing the prototype workaround
unconditionally; I'm just not sure if there's enough consensus on doing
that.

The "missing prototype" check is based on getting a compiler error on a
conflicting prototype, since this just seems more precise and certain
than getting an error from a missing prototype (needs
-Werror=missing-prototypes or -Werror). But I can do it the other way
around if needed.

Changes since v1:
- madvise prototype check changed to not be platforms-specific, and turned into
  CONFIG_MADVISE_MISSING_PROTOTYPE. 

 meson.build  | 17 +++++++++++++++--
 util/osdep.c |  3 +++
 2 files changed, 18 insertions(+), 2 deletions(-)

diff --git a/meson.build b/meson.build
index 2d6601467f..ff5fce693e 100644
--- a/meson.build
+++ b/meson.build
@@ -1705,25 +1705,38 @@ config_host_data.set('CONFIG_EVENTFD', cc.links('''
   int main(void) { return eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC); }'''))
 config_host_data.set('CONFIG_FDATASYNC', cc.links(gnu_source_prefix + '''
   #include <unistd.h>
   int main(void) {
   #if defined(_POSIX_SYNCHRONIZED_IO) && _POSIX_SYNCHRONIZED_IO > 0
   return fdatasync(0);
   #else
   #error Not supported
   #endif
   }'''))
-config_host_data.set('CONFIG_MADVISE', cc.links(gnu_source_prefix + '''
+
+has_madvise = cc.links(gnu_source_prefix + '''
   #include <sys/types.h>
   #include <sys/mman.h>
   #include <stddef.h>
-  int main(void) { return madvise(NULL, 0, MADV_DONTNEED); }'''))
+  int main(void) { return madvise(NULL, 0, MADV_DONTNEED); }''')
+missing_madvise_proto = false
+if has_madvise
+  missing_madvise_proto = cc.links(gnu_source_prefix + '''
+    #include <sys/types.h>
+    #include <sys/mman.h>
+    #include <stddef.h>
+    extern int madvise(int);
+    int main(void) { return madvise(0); }''')
+endif
+config_host_data.set('CONFIG_MADVISE', has_madvise)
+config_host_data.set('CONFIG_MADVISE_MISSING_PROTOTYPE', missing_madvise_proto)
+
 config_host_data.set('CONFIG_MEMFD', cc.links(gnu_source_prefix + '''
   #include <sys/mman.h>
   int main(void) { return memfd_create("foo", MFD_ALLOW_SEALING); }'''))
 config_host_data.set('CONFIG_OPEN_BY_HANDLE', cc.links(gnu_source_prefix + '''
   #include <fcntl.h>
   #if !defined(AT_EMPTY_PATH)
   # error missing definition
   #else
   int main(void) { struct file_handle fh; return open_by_handle_at(0, &fh, 0); 
}
   #endif'''))
diff --git a/util/osdep.c b/util/osdep.c
index 7c4deda6fe..560ce9111a 100644
--- a/util/osdep.c
+++ b/util/osdep.c
@@ -21,20 +21,23 @@
  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  * THE SOFTWARE.
  */
 #include "qemu/osdep.h"
 #include "qapi/error.h"
 
 /* Needed early for CONFIG_BSD etc. */
 
 #ifdef CONFIG_SOLARIS
 #include <sys/statvfs.h>
+#endif
+
+#ifdef HAVE_MADVISE_MISSING_PROTOTYPE
 /* See MySQL bug #7156 (http://bugs.mysql.com/bug.php?id=7156) for
    discussion about Solaris header problems */
 extern int madvise(char *, size_t, int);
 #endif
 
 #include "qemu-common.h"
 #include "qemu/cutils.h"
 #include "qemu/sockets.h"
 #include "qemu/error-report.h"
 #include "qemu/madvise.h"
-- 
2.11.0