Re: Make max_align_t respect _Float128 [version 2]

[Florian Weimer <fweimer at redhat dot com>]

On 09/06/2016 10:40 PM, Joseph Myers wrote:
> On Tue, 6 Sep 2016, Paul Eggert wrote:
>
> > One way to correct the code is to increase malloc's argument up to a multiple
> > of alignof(max_align_t). (One cannot portably use alignof(struct s) due to
>
> Sounds like a defect in C11 to me - none of the examples of flexible array
> members anticipate needing to add to the size to allow for tail padding
> with unknown alignment requirements.

I agree, this is a defect in C99 and C11.  The language hasn't changed 
since C99, and C99 has the same issue because it's unrelated to 
alignment specifiers.  It's a confusion between struct sizes (which are 
multiples of the struct alignment) and object sizes (which are not 
necessarily so).

I have reopened PR66661 with a more elaborate test case which shows that 
GCC packs objects more tightly than the struct alignment would permit.

Thanks,
Florian