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Re: [PATCH] c/67882 - improve -Warray-bounds for invalid offsetof
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Bernd Schmidt <bschmidt at redhat dot com>, Martin Sebor <msebor at gmail dot com>, Joseph Myers <joseph at codesourcery dot com>, Gcc Patch List <gcc-patches at gcc dot gnu dot org>
- Date: Mon, 26 Oct 2015 13:27:53 +0100
- Subject: Re: [PATCH] c/67882 - improve -Warray-bounds for invalid offsetof
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On Mon, Oct 26, 2015 at 1:01 PM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Mon, Oct 26, 2015 at 12:57:53PM +0100, Bernd Schmidt wrote:
>> On 10/26/2015 12:47 PM, Jakub Jelinek wrote:
>>
>> >Because the amount of code that uses this (including GCC itself) is just too
>> >huge, so everywhere in the middle-end we also special case last array members of
>> >structs. While C99+ has flexible array members, e.g. C++ does not, so users
>> >are left with using struct { ... type fld[1]; };
>>
>> Yes, and that case is documented. However, the issue is arrays declared with
>> a larger size than 1 or 0 - is there really code using them as flexible
>> array members?
>
> I believe so, though don't have pointers to that right now. But vaguely
> remember we saw various cases of using 2 or other values too.
Yes, char[4] is quite common (basically making sure there is no appearant
padding behind the array due to alignment - just in case compilers might
be clever because of that).
Richard.
> Jakub