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

[Simon Marchi <simon.marchi@polymtl.ca>]

On 2021-11-04 08:17, Andrew Burgess via Gdb-patches wrote:
> * 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

Just wondering, does anybody care about building GDB with a compiler
other than GCC and Clang?  Because another way that excludes the warning
just for gcc (rather than include it for anything that isn't gcc) would
be (in pseudo code):

diff --git a/gdbsupport/warning.m4 b/gdbsupport/warning.m4
index 46036fa461e8..33a729a60d5d 100644
--- a/gdbsupport/warning.m4
+++ b/gdbsupport/warning.m4
@@ -150,7 +150,7 @@ then
 		[WARN_CFLAGS="${WARN_CFLAGS} $w"],
 		[]
 	      )
-	    else
+	    elif (compiler is not gcc) or (warning is not -Wmissing-prototypes); then
 	      AC_COMPILE_IFELSE(
 		[AC_LANG_PROGRAM([], [])],
 		[WARN_CFLAGS="${WARN_CFLAGS} $w"],

If that works, I think it would be preferable, but otherwise I think
your patch is OK.  Please push whatever makes the most sense to you, so
we can finally get rid of this warning :).

Simon