How to make gcc psABI conformant

[H.J. Lu]

On Wed, Oct 10, 2007 at 09:10:06AM -0400, Daniel Jacobowitz wrote:
> On Wed, Oct 10, 2007 at 06:05:01AM -0700, H.J. Lu wrote:
> > > Isn't that STACK_BOUNDARY?  If not, since you seem to understand the
> > > difference between these variables, could you improve the
> > > documentation?
> > 
> > STACK_BOUNDARY is enforced by hardware. INCOMING_STACK_BOUNDARY is
> > specified by psABI. INCOMING_STACK_BOUNDARY >= STACK_BOUNDARY.
> 
> Great, a third one...

For the backends which support INCOMING_STACK_BOUNDARY, we may
undefine PREFERRED_STACK_BOUNDARY since we can align variables
on stack properly.

> 
> > That is we save the original stack pointer in the frame pointer and
> > align the stack in prologue. It will touch frondend, middleend and
> > backend. Will this scheme work for PowerPC?
> 
> Probably not.  I don't think we have the freedom to abuse the frame
> pointer that way.  But the PowerPC case really ought to be simple,
> modulo correct debug info.
> 

Each backend needs to specify a hard register for the original stack
pointer.  Using the frame pointer on x86 since it is less useful than
others.  Will align stack cause problem for PowerPC?


H.J.