Re: [PATCH] sparse: ignore warning from new glibc headers

From: Ramsay Jones <ramsay@ramsayjones.plus.com>
Date: Jul 17, 2024, 19:20 UTC
Message-ID: <8dd1a2c7-5b9f-4e2f-9c5a-d5d5758714e2@ramsayjones.plus.com>
In-Reply-To: <xmqqr0br26ok.fsf@gitster.g>

On 17/07/2024 19:51, Junio C Hamano wrote:

> Ramsay Jones <ramsay@ramsayjones.plus.com> writes:

[snip]

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>> I mentioned this problem to Luc on the sparse mailing list[1] and
>> he produced a patch which 'fixed' the problem in one way, but
>> caused a different problem[2]. Namely, because git passes -Wvla
>> to gcc, it now issues the 'used vla' warnings, which gcc does
>> not because of some '# pragma GCC diagnostic ignored "-Wvla"' which
>> sparse does not honor! :(
> 
> Sorry, but I do not follow.  Isn't -Wno-vla an instruction to sparse
> to tell it *not* to complain about use of vla?

It's a warning flag for both sparse and gcc. At the time, I was trying to find a solution which didn't disable the warning for gcc at the same time (iff you used sparse as a front-end to gcc, which people on git tend not to do; ie _don't_ use 'cgcc -no-compile' ;) ).

Also, I wanted a solution that didn't require setting SPARSE_FLAGS (SP_EXTRA_FLAGS didn't exist then) in the Makefile (only some people were affected).

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> We do not pass -Wvla or -Wno-vla to sparse ourselves.  Because the
> tool comes from the Linux land where VLA is not welcome, we'd by
> default get the "hey, you used vla here---did you mean it?" error.
> 
> And the patch by Luc Van Oostenryck in the thread you raised at
> around the end of 2023 does apply to the tip and with
> 
> 	SP_EXTRA_FLAGS += -Wno-vla
> 
> in Makefile, sparse seems to be happy when I do "make sparse".

Yes, that works because 'make sparse' does not use cgcc as a front end to gcc, and the command line has -Wvla followed by -Wno-vla, so last one wins (the sparse specific flags come after the gcc flags).

ATB, Ramsay Jones