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

[Simon Marchi via Gdb-patches <gdb-patches@sourceware.org>]

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.

Simon