On 14/11/2019 20:40, selva.n...@gmail.com wrote: > From: Selva Nair <selva.n...@gmail.com> > > Some compilers (e.g., clang) only issue a warning for > unsupported options unless additional flags such > as -Werror are used to convert the warning to an error. > > Add support for extra flags in ACL_CHECK_ADD_COMPILE_FLAGS. > > Note: a similar approach is used in AX_CHECK_COMPILE_FLAG > in autoconf archives.
I'm glad I didn't spend more time on thinking about this earlier today, as you
have almost the same ideas as I had :)
[...snip...]
>
> +# Usage: ACL_CHECK_ADD_COMPILE_FLAGS(flag, [extra-flags])
> +# Some compilers require extra flags to trigger an error on
> +# unsupported options. E.g., clang requires -Werror.
> AC_DEFUN([ACL_CHECK_ADD_COMPILE_FLAGS], [
> old_cflags="$CFLAGS"
> - CFLAGS="$1 $CFLAGS"
> - AC_MSG_CHECKING([whether the compiler acceppts $1])
> - AC_COMPILE_IFELSE([AC_LANG_PROGRAM()], [AC_MSG_RESULT([yes])],
> + CFLAGS="$2 $1 $CFLAGS"
> + AC_MSG_CHECKING([whether the compiler accepts $1])
> + AC_COMPILE_IFELSE([AC_LANG_PROGRAM()], [AC_MSG_RESULT([yes])];
> CFLAGS="$1 $old_cflags",
My idea was just to add -Werror right in the line above, and not extend the
ACL_CHECK_ADD_COMPILE_FLAGS macro with another argument.
But I stopped when I realized that GCC has some quirks as well, as I needed to
ponder about this a bit.
Clang is fairly consistent:
* first with an unknown -Wno-* argument
$ clang-6.0 -o test test.c -Wall -Wno-non-existing-flag
warning: unknown warning option '-Wno-non-existing-flag'; did you mean
'-Wno-non-virtual-dtor'? [-Wunknown-warning-option]
$ clang-6.0 -o test test.c -Wall -Wno-non-existing-flag -Werror
error: unknown warning option '-Wno-non-existing-flag'; did you mean
'-Wno-non-virtual-dtor'? [-Werror,-Wunknown-warning-option]
* then with an unknown -W* argument (without the no- prefix)
$ clang-6.0 -o test test.c -Wall -Wnon-existing-flag
warning: unknown warning option '-Wnon-existing-flag'; did you mean
'-Wnon-virtual-dtor'? [-Wunknown-warning-option]
$ clang-6.0 -o test test.c -Wall -Wnon-existing-flag -Werror
error: unknown warning option '-Wnon-existing-flag'; did you mean
'-Wnon-virtual-dtor'? [-Werror,-Wunknown-warning-option]
This is consistent and I can live with this behavior, using -Werror to bail
out on warnings.
So lets running the same tests with GCC:
* first with an unknown -Wno-* argument
$ gcc -o test test.c -Wall -Wno-non-existing-flag
(no error nor warning)
$ gcc -o test test.c -Wall -Wno-non-existing-flag -Werror
(no error nor warning)
* then with an unknown -W* argument (without the no- prefix)
$ gcc -o test test.c -Wall -Wnon-existing-flag
gcc: error: unrecognized command line option ‘-Wnon-existing-flag’
I think you said it pretty well in your mail:
> Darn compilers and darn -Werror
So your change does improve Clang ... I dunno what we will do with GCC.
--
kind regards,
David Sommerseth
OpenVPN Inc
signature.asc
Description: OpenPGP digital signature
_______________________________________________ Openvpn-devel mailing list Openvpn-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/openvpn-devel
