Re: gdb: disable -Wmissing-prototypes warning w/gcc

[Andrew Burgess <aburgess@redhat.com>]

* Mike Frysinger via Gdb-patches <gdb-patches@sourceware.org> [2021-11-04 08:00:53 -0400]:

> On 03 Mar 2020 17:34, Simon Marchi wrote:
> > While compiling with clang, I noticed it didn't catch cases where my
> > function declaration didn't match my function definition.  This is
> > normally caught by gcc with -Wmissing-declarations.
> > 
> > On clang, this is caught by -Wmissing-prototypes instead.
> > 
> > Note that on gcc, -Wmissing-prototypes also exists, but is only valid
> > for C and Objective-C.  It gets correctly rejected by the configure
> > script since gcc rejects it with:
> > 
> >     cc1plus: error: command line option '-Wmissing-prototypes' is valid for C/ObjC but not for C++ -Werror
> > 
> > So this warning flag ends up not used for gcc (which is what we want).
> 
> so ccache has a long standing bug where it mishandles -Werror with other
> -W options causing the configure test to pass when it shouldn't.
> https://github.com/ccache/ccache/issues/738
> 
> that means ccache+gcc builds of gdb are full of annoying logs:
>   CXX    cli/cli-decode.o
> cc1plus: warning: command-line option ‘-Wmissing-prototypes’ is valid for C/ObjC but not for C++
> 
> i get that the configure script here isn't wrong, but there aren't any
> knobs in here that i can tweak to workaround the issue either, and i'm
> trying to avoid carrying patches in all my local branches, and configure
> files are kind of meant to deal with all sorts of system warts.
> 
> so random terrible idea below.
> -mike
> 
> --- a/gdbsupport/warning.m4
> +++ b/gdbsupport/warning.m4
> @@ -51,10 +51,15 @@ build_warnings="-Wall -Wpointer-arith \
>  -Wdeprecated-copy-dtor \
>  -Wredundant-move \
>  -Wmissing-declarations \
> --Wmissing-prototypes \
>  -Wstrict-null-sentinel \
>  "
>  
> +# GCC doesn't support this flag currently, and probing via ccache breaks.
> +# https://github.com/ccache/ccache/issues/738
> +if test "${GCC}" != yes ; then
> +  build_warnings="$build_warnings -Wmissing-prototypes"
> +fi
> +
>  case "${host}" in
>    *-*-mingw32*)
>      # Enable -Wno-format by default when using gcc on mingw since many

I also tried to solve this issue, but went in a different direction:

  https://sourceware.org/pipermail/gdb-patches/2021-September/182148.html

However, Pedro objected.  He would prefer to see a solution exactly
like you proposed above.  The only reason I didn't immediately knock
out a patch was that I didn't know how to check if GCC was the
compiler or not.  Turns out it's pretty easy :)

So, what you wrote gets my +1, and based on the feedback on my thread,
I don't think anyone else will object.

Thanks,
Andrew