Alpha Assembly

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.

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.

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.

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

• Alpha Architecture Chip Documents
  • Compiler Writer's Guide for the Alpha 21264
• Alpha Assembly for Linux/UNIX
• Introduction to Alpha
• Re: Question re: Alpha asm code