Re: [PATCH] gdbsupport: better detection of -Wmissing-prototypes support

[Pedro Alves <pedro@palves.net>]

On 2021-09-24 3:22 p.m., Simon Marchi wrote:
> 
> 
> On 2021-09-24 10:06 a.m., Pedro Alves wrote:
>> On 2021-09-24 2:40 p.m., Simon Marchi via Gdb-patches wrote:
>>> On 2021-09-24 9:16 a.m., Andrew Burgess wrote:
>>>> It has been pointed out to me on IRC (thanks Simon), that this issue
>>>> is not GCC, but ccache:
>>>>
>>>>   https://github.com/ccache/ccache/issues/738#issuecomment-740133374
>>>>
>>>> So this patch certainly shouldn't go in as it is currently written.
>>>>
>>>> It's still pretty annoying seeing those warnings though, so I wonder
>>>> if we can consider having a work around for this ccache issue in the
>>>> GDB configure scripts?
>>>>
>>>> Maybe something as simple as setting CCACHE_DISABLE in the environment
>>>> prior to running the AM_GDB_WARNINGS checks?
>>>>
>>>> All ideas welcome...
>>>
>>> Either way would be fine with me:
>>>
>>>  - to use AC_LINK_IFELSE all the time (I don't think the execution time
>>>    would be significantly higher)
>>>  - to set CCACHE_DISABLE during the execution of AM_GDB_WARNINGS
>>
>> Does working around this in configure tests still mean that when using ccache
>> for really building gdb, ccache will still misreorder arguments and thus
>> potentially a -Wmissing-prototypes warning would not be turned into an error?
> 
> I think it's only the "-Wmissing-prototypes is useless in C++" warning
> that has this order problem.  If you were compiling something in C and
> was missing a prototype, that warning would be not be affected by the
> order bug (although I haven't tried).
> 
> By working around in the problem in configure, that means
> -Wmissing-prototypes will not be present when compiling with GCC (as it
> does nothing in C++), so there's nothing to miss here.
> 
>> So, here's another option, I think:
>>
>> #3 - drop -Wmissing-prototypes completely.
>>
>> As the GCC warning says,
>>
>>   cc1plus: warning: command line option ‘-Wmissing-prototypes’ is valid for C/ObjC but not for C++
>>
>> it's only valid for C, not C++.  Do we compile anything with a C compiler nowadays?
> 
> It's there because it does something for clang in C++, see:
> 
>   https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=a0761e34f054767de6d6389929d27e9015fb299b
> 
> If we find that the rationale for having it there isn't valid anymore,
> we can remove it.

How about skipping checking for -Wmissing-prototypes support if compiling with gcc then?