Assembly Primer Part 4 — Hello World — PPC

These are my notes for where I can see PPC varying from ia32, as presented in the video Part 4 — Hello World.  Let me know if I’ve missed something important, obvious or got something wrong.

http://www.ibm.com/developerworks/library/l-ppc/ gives a good starting overview of PPC asm, including syscalls.  The syscall number goes into gpr0 and the args in gpr3 and following, so JustExit.s becomes:

.text
.globl _start

_start:
    li 0,1 # load 1 into reg 0
    li 3,0 # load 0 into reg 3
    sc     # system call

Simple enough.

Modifying the provided HelloWorldProgram.s example (and using the example from the above link) yields

.data

HelloWorldString:
    .ascii "Hello World\n"

.text

.globl _start

_start:
    # Load all the arguments for write ()

    li   0, 4  # syscall number of 4 (write)
    li   3, 1  # filenumber 1 (stdout)
    lis  4, HelloWorldString@ha   # load upper 16 bits of addr
    addi 4, 4, HelloWorldString@l # add lower 16 bits of addr
    li   5, 12 # length of string
    sc

    # exit the program
    li 0,1
    li 3,0
    sc

There’s some subtlety in the @ha and @l high and low parts of addresses that I don’t yet have my head around fully, but I’ll be coming back to this in a later part.

Previous assembly primer notes…

Part 1 — System Organization — PPC — SPU
Part 2 — Memory Organisation — SPU
Part 3 — GDB Usage Primer — PPC & SPU