Re: aligned attribute

[Maurizio Vitale <maurizio.vitale@polymath-solutions.com>]

Thanks. Now to add to my confusion, on my system __alignof(long  
double) returns 16, which I presume means that all allocation,  
static, dynamic and automatic for long double objects are 16 byte  
aligned.


On Dec 20, 2006, at 8:37 AM, Andrew Haley wrote:

> Maurizio Vitale writes:
>> But when I move to my real application (an event-driven simulator) I
>> get stack allocated objects on 8-byte boundaries.
>>
>> Now, my reading of the documentation is that the aligned attribute
>> (when used for types, as in the example I gave) applies to all
>> allocations (global, auto and heap). Is there any place where it is
>> said otherwise? Regardless of the documentation, what does the
>> implementation do?
>
> You can't get alignment any greater than the alignment of the stack
> pointer.  The alignment of the stack pointer is defined the the ABI of
> the particular target you're using.  I think it's 16 for x86
> processors, but the processor itself doesn't enforce that: it varies
> across operating systems and processor variants.
>
>> This lead me to believe that every time a variable of type S is
>> allocated, the requested alignment is used (modulo linker
>> limitations of above).
>
> Sure, but that only really applies to statically allocated objects.  I
> guess no-one appreciated that someone might want to use it for
> auto variables.
>
> Andrew.
>
>