Re: some basic problems with ppc assembler
On Wed, 25 Jun 2003, Oliver Ripka wrote:
> I try to understand some ppc-assembler-code but it is harder than
> x86 to me because of the missing documentation. I have a big reference
> from ibm here. And some websites which deal with this topic.
There's lots of documentation about PPC assembler on the Motorola website, too.
> .LC0: //I guess this means .LC0
> .string "Hello World" //is a global string
> .globl main //within the main label.
>
> .type main, @function //whats that for?
> main:
> stwu 1,-32(1) //I do not understand this.
Store Word Unsigned, i.e. save r1 to address r1-32.
> mflr 0 //Does this
Move From LR (Link Register). LR is used to store the return address for a
subroutine, i.e. save the return address in r0.
I.e. move LR to r0.
> stw 31,28(1) //setup some
Store r31 to address r1+28.
> stw 0,36(1) //GPRs for the
Store r0 to address r1+36
> mr 31,1 //begin of the code??
Move r1 to r31.
> lis 9,.LC0@ha //this is
> la 3,.LC0@l(9) //fine
OK
> crxor 6,6,6 //this clears the contend of crb6 right?
> bl printf //mhh..
Branch with Link Register, i.e. subroutine call
> li 0,0 //set the GPR0 to completly to zeros
> mr 3,0 //why that?? since 0 OR 0 is 0 it just
> //moves GPR0 to GRP3, right?
Yep
> lwz 11,0(1) //GPR3 pointing to 0?
Load r11 from address r1
> lwz 0,4(11) //GPR0 pointing to 4?
Load r0 from address r11+4
> mtlr 0 //again this mt* function what does it?
Move To Link Register, i.e. restore the return address
> lwz 31,-4(11) //...
Load r31 from address r11-4
> mr 1,11 //..
Move r11 to r1
> blr //...
Branch to Link Register, i.e. return from subroutine.
> TIA
You're welcome ;-)
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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