[Libguestfs] [libnbd PATCH 3/5] libev: Check for old compiler
At some point GCC added some optimisations and checks that started emitting
warnings on harmless code:
...dereferencing type-punned pointer will break strict-aliasing rules...
This was later fixed, but can still break the build (or report warnings) on old
GCCs (e.g. 7.5.0) when building the libev example.
Signed-off-by: Martin Kletzander <mkletzan(a)redhat.com>
---
configure.ac | 24 ++++++++++++++++++++++++
1 file changed, 24 insertions(+)
diff --git a/configure.ac b/configure.ac
index 19b7bfdb5d2a..3b51354346cc 100644
--- a/configure.ac
+++ b/configure.ac
@@ -247,6 +247,30 @@ PKG_CHECK_MODULES([LIBEV], [libev], [
AC_MSG_WARN([ev.h not found, some examples will not be compiled])
])
])
+
+AS_IF([test "x$LIBEV_LIBS" != "x"], [
+ old_CFLAGS="$CFLAGS"
+ CFLAGS="-Werror=strict-aliasing -O2"
+ AC_MSG_CHECKING([if the compiler is new enough for good aliasing rules])
+ AC_COMPILE_IFELSE([
+ AC_LANG_PROGRAM([
+ #include <ev.h>
+
+ static void cb (struct ev_loop *l, ev_timer *t, int e) { }
+ static ev_timer timer;
+ ], [
+ ev_timer_init (&timer, cb, 0, .1);
+ ])
+ ], [
+ AC_MSG_RESULT([yes])
+ ], [
+ AC_MSG_RESULT([no])
+ AC_SUBST([LIBEV_CFLAGS], [""])
+ AC_SUBST([LIBEV_LIBS], [""])
+ AC_MSG_WARN([compiler is probably too old to compile with libev without errors,
some examples will not be compiled])
+ ])
+ CFLAGS="$old_CFLAGS"
+])
AM_CONDITIONAL([HAVE_LIBEV], [test "x$LIBEV_LIBS" != "x"])
dnl FUSE 3 is optional to build the nbdfuse program.
--
2.31.1