I've noticed recently an annoying quantity of error messages like the
following in builds in various places:
gcc: error: unrecognized command line option ‘-Wunknown-warning-option’
This didn't really make sense because OVS checks whether the compiler
supports warning options before it uses them. Looking closer, the GCC
manual has a note that explains the issue:
When an unrecognized warning option is requested (e.g.,
'-Wunknown-warning'), GCC emits a diagnostic stating that the
option is not recognized. However, if the '-Wno-' form is used,
the behavior is slightly different: no diagnostic is produced for
'-Wno-unknown-warning' unless other diagnostics are being
produced. This allows the use of new '-Wno-' options with old
compilers, but if something goes wrong, the compiler warns that
an unrecognized option is present.
Thus, we can properly check only for the *positive* version of a warning
option, so this commit makes the OVS tests do that.
Fixes: a7021b08b0d5 ("configure: Disable -Wnull-pointer-arithmetic Clang
warning.")
Signed-off-by: Ben Pfaff <b...@ovn.org>
---
acinclude.m4 | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/acinclude.m4 b/acinclude.m4
index 0690baedfb9d..8d850349817f 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -996,7 +996,11 @@ AC_DEFUN([_OVS_CHECK_CC_OPTION], [dnl
dnl gcc: unrecognized option '-Qunused-arguments'
dnl 0
dnl %
- CFLAGS="$CFLAGS $WERROR $1"
+ dnl
+ dnl In addition, GCC does not complain about a -Wno-<foo> option that
+ dnl it does not understand, unless it has another error to report, so
+ dnl instead of testing for -Wno-<foo>, test for the positive version.
+ CFLAGS="$CFLAGS $WERROR m4_bpatsubst([$1], [-Wno-], [-W])"
AC_COMPILE_IFELSE(
[AC_LANG_SOURCE([int x;])],
[if test -s conftest.err && grep "unrecognized option" conftest.err
--
2.16.1
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