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

From: Ramsay Jones <ramsay@ramsayjones.plus.com>
Date: Jul 17, 2024, 18:40 UTC
Message-ID: <9bdac465-5f43-42de-9cad-e6c43a5a53cc@ramsayjones.plus.com>
In-Reply-To: <xmqqikx42c42.fsf@gitster.g>

On 17/07/2024 17:54, Junio C Hamano wrote:

Show 16 quoted lines

> Đoàn Trần Công Danh <congdanhqx@gmail.com> writes:
> 
>> With at least glibc 2.39, glibc provides a function declaration that
>> matches with this POSIX interface:
>>
>>     int regexec(const regex_t *restrict preg, const char *restrict string,
>>            size_t nmatch, regmatch_t pmatch[restrict], int eflags);
>>
>> such prototype requires variable-length-array for `pmatch'.
>> ...
>> Thus, sparse reports this error:
>>
>>> ../add-patch.c: note: in included file (through ../git-compat-util.h):
>>> /usr/include/regex.h:682:41: error: undefined identifier '__nmatch'
>>> /usr/include/regex.h:682:41: error: bad constant expression type
>>> /usr/include/regex.h:682:41: error: Variable length array is used.

Yes, I noted this about 2 years ago! If memory serves, it was when the libc6-dev package went from v2.31 to 2.35 (well 2.31-0ubuntu9.9).

As I said at the time, this only affected glibc platforms (so not newlib on cygwin for example) of a certain vintage, so I just added

  SPARSE_FLAGS += -D__STDC_NO_VLA__

to my config.mak file.

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> I get the same with 
> 
> 	$ sparse --version
> 	v0.6.4-66-g0196afe1
>

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! :(

So, his patch was not applied in the end.

ATB, Ramsay Jones

The sparse mailing list archive can be found at:

   https://lore.kernel.org/linux-sparse

The messages below were from December 2023 (approx. 20/12/2023)

[1] Message-ID: <6f853a6b-9ac3-4bfd-a968-89d43fbcce2a@ramsayjones.plus.com> [2] Message-ID: <24cb6194-d04d-4c80-bd95-4f7356667884@ramsayjones.plus.com>