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Re: EABI stack alignment for ppc


Olivier Hainque <hainque@adacore.com> writes:

> Hello,
> 
> PPC EABI targets are currently configured with both BIGGEST_ALIGNMENT and
> PREFERRED_STACK_BOUNDARY set to 128, I believe to accomodate
> 
>   "a long double member within a structure or union shall start at the lowest
>    available offset aligned on a 16byte boundary"

BIGGEST_ALIGNMENT is 128 for a number of reasons, but
PREFERRED_STACK_BOUNDARY is 128 primarily so that code compiled with
-meabi can also be used on Linux and other SVR4 targets, and for
Altivec support.

> Now, I'm a bit unclear on the meaning of the ABI statement quoted above, and
> on the real implications this should have in the compiler. 
> 
> Does it imply that a long double field *address* should always be a multiple
> of 16, or just that the *offset* should be such a multiple ?

It says offset, so it probably means offset.


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