[Qemu-devel] [PATCH v3] configure: sanity check the glib library that pkg-config finds

["Daniel P. Berrange" <berrange@redhat.com>]

Developers on 64-bit machines will often try to perform a
32-bit build of QEMU by running

  ./configure --extra-cflags="-m32"

Unfortunately if PKG_CONFIG_LIBDIR is not set to point to
the location of the 32-bit pkg-config files, then configure
will silently pick up the 64-bit pkg-config files and still
succeed.

This causes a problem for glib because it means QEMU will
be pulling in /usr/lib64/glib-2.0/include/glibconfig.h
instead of /usr/lib/glib-2.0/include/glibconfig.h

This causes problems because the 'gsize' type (defined as
'unsigned long') will no longer be fully compatible with
the 'size_t' type (defined as 'unsigned int'). Although
both are the same size, the compiler refuses to allow
casts from 'unsigned long *' to 'unsigned int *' as they
are different pointer types. This results in non-obvious
compiler errors when building QEMU eg

qga/commands-posix.c: In function ‘qmp_guest_set_user_password’:
qga/commands-posix.c:1912:55: error: passing argument 2 of ‘g_base64_decode’ from incompatible pointer type [-Werror=incompatible-pointer-types]
     rawpasswddata = (char *)g_base64_decode(password, &rawpasswdlen);
                                                            ^
In file included from /usr/include/glib-2.0/glib.h:35:0,
                 from qga/commands-posix.c:14:
/usr/include/glib-2.0/glib/gbase64.h:52:9: note: expected ‘gsize * {aka long unsigned int *}’ but argument is of type ‘size_t * {aka unsigned int *}’
 guchar *g_base64_decode         (const gchar  *text,
         ^
cc1: all warnings being treated as errors

To detect this problem, add a check to configure that
verifies that GLIB_SIZEOF_SIZE_T matches sizeof(size_t).
If this fails print a warning suggesting that the dev
probably needs to set PKG_CONFIG_LIBDIR.

On Fedora x86_64 it passes with any of:

 # ./configure
 # PKG_CONFIG_LIBDIR=/usr/lib/pkgconfig ./configure --extra-cflags="-m32"
 # PKG_CONFIG_LIBDIR=/usr/lib64/pkgconfig ./configure --extra-cflags="-m64"

And fails with a mis-match

 # PKG_CONFIG_LIBDIR=/usr/lib64/pkgconfig ./configure --extra-cflags="-m32"
 # PKG_CONFIG_LIBDIR=/usr/lib/pkgconfig ./configure --extra-cflags="-m64"

ERROR: sizeof(size_t) doesn't match GLIB_SIZEOF_SIZE_T.
       You probably need to set PKG_CONFIG_LIBDIR
       to point to the right pkg-config files for your
       build target

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---

Changed in v3:

 - Removed use of G_STATIC_ASSERT in favour of simplified
   version of QEMU_BUILD_BUG_ON to avoid unused typedef
   warning

 configure | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/configure b/configure
index 44ac9ab..fbd2482 100755
--- a/configure
+++ b/configure
@@ -2997,6 +2997,30 @@ for i in $glib_modules; do
     fi
 done
 
+# Sanity check that the current size_t matches the
+# size that glib thinks it should be. This catches
+# problems on multi-arch where people try to build
+# 32-bit QEMU while pointing at 64-bit glib headers
+cat > $TMPC <<EOF
+#include <glib.h>
+#include <unistd.h>
+
+#define QEMU_BUILD_BUG_ON(x) \
+  typedef char qemu_build_bug_on[(x)?-1:1] __attribute__((unused));
+
+int main(void) {
+   QEMU_BUILD_BUG_ON(sizeof(size_t) != GLIB_SIZEOF_SIZE_T);
+   return 0;
+}
+EOF
+
+if ! compile_prog "-Werror $CFLAGS" "$LIBS" ; then
+    error_exit "sizeof(size_t) doesn't match GLIB_SIZEOF_SIZE_T."\
+               "You probably need to set PKG_CONFIG_LIBDIR"\
+	       "to point to the right pkg-config files for your"\
+	       "build target"
+fi
+
 # g_test_trap_subprocess added in 2.38. Used by some tests.
 glib_subprocess=yes
 if ! $pkg_config --atleast-version=2.38 glib-2.0; then
-- 
2.5.0