Re: [PATCH] [gdb/testsuite] Fix gdb.arch/i386-avx.exp with clang

Tom de Vries via Gdb-patches
2021-11-05T13:36:44Z

On 11/5/21 2:20 PM, Pedro Alves wrote:
> On 2021-11-05 13:15, Tom de Vries wrote:
>> On 11/5/21 1:55 PM, Pedro Alves wrote:
>>> On 2021-11-05 12:23, Tom de Vries via Gdb-patches wrote:
>>>
>>>>> No, but in gdb/testsuite/lib/attribute.h we do setup a compatibility
>>>>> macro for 'noclone', so there's definitely precedent for using
>>>>> attributes that might not be supported everywhere.
>>>>>
>>>>
>>>> Right, I'm aware of this, but that's a typical case where we have no
>>>> portable alternative.
>>>
>>> We actually do -- _Alignas is standard C11. This fixes the test as well:
>>>
>>> _Alignas(32) v8sf_t data[] =
>>>
>>
>> I was referring to the noclone, but ok, I was not aware of the _Alignas,
>> good to know, thanks.
>>
>> Anyway, in the latest version this is not relevant anymore, since the
>> precise alignment implementation has an extra benefit, as explained in
>> the post.
>>
>
> OOC, is that benefit important here?
>

So, this is the post I mentioned (
https://sourceware.org/pipermail/gdb-patches/2021-November/183183.html ).

Well, the benefit is that it prevents accidental overalignment, which is
the reason that this problem escaped detection and/or fixing for so long.

Without that, I could do a thinko and specify too small an alignment and
have the test passing accidentally, only to fail in a different setup.

Thanks,
- Tom