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SubjectRe: BUG: GCC-4.4.x changes the function frame on some functions
On Thu, Nov 19, 2009 at 03:17:16PM -0500, Steven Rostedt wrote:
> On Thu, 2009-11-19 at 15:05 -0500, Steven Rostedt wrote:
>
> > Well, other archs use a register to store the return address. But it
> > would also be easy to do (pseudo arch assembly):
> >
> > <function>:
> > mov lr, (%sp)
> > add 8, %sp
> > blr __fentry__
>
> Should be bl __fentry__ for "branch and link".
>
> > sub 8, %sp
> > mov (%sp), lr
> >
> >
> > That way the lr would have the current function, and the parent would
> > still be at 8(%sp)
>
> Actually, if we add a new profiler and can make our own specification, I
> would say that the add and sub lines be the responsibility of
> __fentry__. Then we would have:
>
> <function>:
> mov lr, (%sp)
> bl __fentry__
> mov (%sp), lr
>
> If sp points to the current content, then replace (%sp) above with
> -8(%sp). Then the implementation of a nop __fentry__ would simply be:
>
> __fentry__:
> blr


Good point!


> For anything more elaborate, __fentry__ would be responsible for all
> adjustments.


Yep. The more we control it from __fentry__, the less we fall
down into unexpected surprises.



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