From:	MERC::"uunet!CRVAX.SRI.COM!RELAY-INFO-VAX" 22-MAY-1992 19:14:31.65
To:	Mark-Tarbell@suite.com, INFO-VAX@SRI.COM
CC:	
Subj:	Re: Access to caller's SP

I posted the following code:

        .title  fixsp
        .entry  fixsp,^m<iv>
        subl2   #10000,sp
        movl    16(fp),r0
        movl    12(fp),fp
        jmp     (r0)
        .end

> However... don't you also need to restore ALL of
> the saved context from the call frame? Things such
> as all of the registers, the condition handler (if
> any), etc?  Won't these things be lost otherwise?
> Is it necessary to restore the (uh-oh) PSL?

We have to restore everything we have changed. If we change R2, then we need
to restore R2 from the call-stack-frame. But I only changed R0 and compilers
do not assume R0 an R1 unchanged after a CALLx instruction.

I do not think you need to restore the PSW (not the PSL !) with the N,Z,V and
C bits, because the CALLx instruction clears them anyway.

                                                          Arne Vajhxj

Arne Vajhxj                             local DECNET:  KO::ARNE
Computer Department                     PSI:           PSI%238310013040::ARNE
Business School of Southern Denmark     Internet:      ARNE@KO.HHS.DK