| Message ID | 20180918091120.14083-1-blp@ovn.org |
|---|---|
| State | Accepted |
| Headers | show |
| Series | [ovs-dev] acinclude.m4: Really check whether GCC support -Wno-null-pointer-arithmetic. | expand |
Ben Pfaff <blp@ovn.org> writes: > 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 <blp@ovn.org> > --- I didn't get a chance to test this out, but the change looks sane. Acked-by: Aaron Conole <aconole@redhat.com>
On Wed, Sep 26, 2018 at 01:26:46PM -0400, Aaron Conole wrote: > Ben Pfaff <blp@ovn.org> writes: > > > 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 <blp@ovn.org> > > --- > > I didn't get a chance to test this out, but the change looks sane. > > Acked-by: Aaron Conole <aconole@redhat.com> Thanks. I applied this to master.
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
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 <blp@ovn.org> --- acinclude.m4 | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)