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Re: getcontext() on ppc32 destroys saved parameter 1 in caller's frame

On Mon, Aug 30, 2004 at 02:01:27PM -0500, Steve Munroe wrote:
> Jakub Bogusz <> wrote on 08/29/2004 12:25:25 PM:
> > GLIBC_2.3.4 getcontext() on ppc32 changes the value of the first
> > parameter passed to caller's function.
> > It's caused by the first instruction of __getcontext()
> > (sysdeps/unix/sysv/linux/powerpc/powerpc32/getcontext.S:29):
> > 
> > ENTRY(__getcontext)
> >         stw     r3,_FRAME_PARM_SAVE1(r1)
> > 
> > __getcontext doesn't have its own stack frame, so it uses caller's
> > stack frame, thus destroying it...
> > 
> > The same applies to GLIBC_2.3.4 swapcontext(), but it may be less/not(?)
> > harmful as successful swapcontext() never returns.
> > 
> Actually the problem is a little different. The PPC32 ABI is different 
> from the PPC64 ABI in that it does not allocate space for the first 
> 8-parms on in the stack frame. So the attempt to save r3 into the parm 
> save area (there is none in this frame) is storing over the variable "a". 
> So for PPC32 need to use negative offsets before pushing the small frame 
> that getcontext uses. Also getcontext should be returning 0 (in r3) to 
> indicate success.
> Have you opened a buzilla for this?

No; I can, if really needed. In the shortage of time it was easier/faster
to just send an e-mail...

Jakub Bogusz
PLD Team

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