Re: Alpha assembly language - ldah/lda after jsr

On Thu, 8 Oct 2003, Timothy Jones wrote:


> ldah/lda pair of instructions to load the $gp after a function call.


If it is assembler code /you/ write, then use the ldgp instruction
instead.


(it is not a good idea to disassemble alpha object code, fiddle with it,
and then reassemble it unless you know what you are doing)


ldgp is actually not a real instruction but a socalled pseudoinstruction
that expands at assembly-time to whatever the assembler deems necessary to
get the right value loaded into the global pointer register ($gp).


The really important part is that the address you specify must be the
address of the ldgp pseudoinstruction itself. You usually use a register
for that purpose, the return address register ($ra) seems particularly
handy right after a jsr, don't you think? ;)


> which is all very well but if I want to change the schedule slightly
> by adding a nop like this:


And then it obviously goes wrong because you use the address of the nop...


(or rather, an incorrect displacement relative to  $ra, to get the address
to load $gp from, hence you get an incorrect $gp value)


> I've already been reading the Assembly Language
> Programmer's Guide without much luck.


Try again...


-Peter


"People seem to misinterpret complexity as sophistication." -- Niklaus Wirth

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