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Re: [PATCH, libgcc]: Avoid warning: array subscript is above array bounds when compiling crtstuff.c
- From: Richard Biener <richard dot guenther at gmail dot com>
- To: Jakub Jelinek <jakub at redhat dot com>
- Cc: Uros Bizjak <ubizjak at gmail dot com>, Ian Lance Taylor <iant at google dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>
- Date: Tue, 11 Mar 2014 11:58:01 +0100
- Subject: Re: [PATCH, libgcc]: Avoid warning: array subscript is above array bounds when compiling crtstuff.c
- Authentication-results: sourceware.org; auth=none
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On Mon, Mar 10, 2014 at 11:14 AM, Jakub Jelinek <jakub@redhat.com> wrote:
> On Mon, Mar 10, 2014 at 11:10:05AM +0100, Uros Bizjak wrote:
>> > Well, better is non-obvious, while it is smaller (which is good for
>> > initialization and thus rarely executed code), the common case is that
>> > *jcr_list is 0 (gcj is used rarely these days) and for the common case it is
>> > one instruction longer.
>> > Perhaps at least use if (__builtin_expect (*jcr_list != NULL, 0))?
>> > Otherwise looks good to me.
>>
>> Following source:
>>
>> void frame_dummy (void)
>> {
>> void **jcr_list = __JCR_LIST__;
>> if (__builtin_expect (*jcr_list != 0, 0))
>> register_classes (jcr_list);
>> }
>>
>> generates exactly the same code while avoiding the warning. So,
>> following your concern, I am testing following patch:
>
> But then the asm is gone and it can start to break any time soon.
> For GCC __JCR_LIST__ is simply a zero sized local array and thus
> dereferencing it's first element is invalid. It doesn't know that we use
> linker magic to populate the array.
You can also declare it extern and define the symbol in a global asm ...
Richard.
> Jakub