Difference between revisions of "Alpha Assembly"

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Latest revision as of 18:07, 29 August 2019

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.[1]

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.[1]

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.[1]

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

References

  1. 1.0 1.1 1.2 Template:Cite web