Gareth: Imported from http://web.archive.org/web/20100713091906/http://www.alphalinux.org/wiki/index.php?title=Alpha_Assembly&action=edit

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Imported from http://web.archive.org/web/20100713091906/http://www.alphalinux.org/wiki/index.php?title=Alpha_Assembly&action=edit

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== Registers ==

The Alpha has split integer and floating-point register files. It has 32 64-bit wide integer and 32 64-bit wide floating-point registers.<ref name="Alpha Architecture Handbook">{{cite web
|url=http://h18002.www1.hp.com/alphaserver/technology/literature/alphaahb.pdf|title=Alpha Architecture Handbook|year=1998|month=October|format=PDF|publisher=Compaq Computer Corporation}}</ref>

=== Integer Registers ===

Of the 32 integer registers, 12 are temporary registers, 6 are saved across function calls, and 6 are for passing arguments. The '''$31''' register always holds the value 0. Writes to it are ignored.<ref name="Alpha Architecture Handbook" />

{| class="wikitable" style="font-size:97%;"
|-
! Register
! Alternate Name
! Preserved?
! Purpose
|-
! $0
| $v0 || No || Return Value
|-
! $1-$8
| $t0-$t7 || No || Temporary Registers
|-
! $9-$14
| $s0-$s5 || Yes || Saved Registers
|-
! $15
| $s6 or $fp || Yes || Saved Register or Frame Pointer
|-
! $16-$21
| $a0-$a5 || No || Function Arguments
|-
! $22-$25
| $t8-$t11 || No || Temporary Registers
|-
! $26
| $ra || Yes || Function Return Address
|-
! $27
| $pv or $t12 || No || Procedure Value or Temporary Register
|-
! $28
| $at || No || Reserved for Assembler
|-
! $29
| $gp || No || Global Pointer
|-
! $30
| $sp || Yes || Stack Pointer
|-
! $31
| $zero || || Zero Sink
|}

=== Floating-Point Registers ===

Of the 32 floating-point registers, 15 are temporary registers, 8 are saved across function calls, and 6 are for passing arguments. The '''$f31''' register always holds the value 0.0. Writes to it are ignored.<ref name="Alpha Architecture Handbook" />

{| class="wikitable" style="font-size:97%;"
|-
! Register
! Preserved?
! Purpose
|-
! $f0
| No || Return Value
|-
! $f1
| No || Return Value of Imaginary Part
|-
! $f2-$f9
| Yes || Saved Registers
|-
! $f10-$f15
| No || Temporary Registers
|-
! $f16-$f21
| No || Function Arguments
|-
! $f22-$f30
| No || Temporary Registers
|-
! $f31
| || Zero Sink
|}

== Hello, World! ==

# hello.S
# gcc hello.S -o hello
# ./hello

.data
PRINT: .ascii "Hello, World!\n"

.text
.align 4
.set noreorder
.arch ev4
.globl main
.ent main

main: ldgp $gp,0($27) # load global pointer (necessary)
stq $26,0($sp) # setup stack pointer

lda $16,PRINT # load format string
# $16 is first argument to functions
jsr $26,printf # call printf
ldgp $gp,0($26) # reload global pointer
# (necessary after function calls)

mov $31,$0 # return val = 0
ldq $26,0($sp) # clean up stack
ret $31,($26),1 # return, (1 signifies return from a procedure)
.end main

== External Links ==
* [http://h18002.www1.hp.com/alphaserver/technology/chip-docs.html Alpha Architecture Chip Documents]
** [http://h18002.www1.hp.com/alphaserver/technology/literature/cmpwrgd.pdf Compiler Writer's Guide for the Alpha 21264]
* [http://mattst88.com/programming/?page=alpha-asm Alpha Assembly for Linux/UNIX]
* [http://www.cs.hut.fi/~cessu/compilers/alpha-intro.html Introduction to Alpha]
* [http://lkml.org/lkml/1998/3/29/96 Re: Question re: Alpha asm code]

== References ==
<references />

[[Category:Programming]]

Alpha Assembly - Revision history

Gareth: Imported from http://web.archive.org/web/20100713091906/http://www.alphalinux.org/wiki/index.php?title=Alpha_Assembly&action=edit