HP UX Developer Tools manual Register Procedure Calling Conventions, Register Synonyms Description

Program Structure

Registers and Register Mnemonics

Some additional predefined register mnemonics are provided in “Register Procedure Calling Conventions” on page 28 to match the standard procedure-calling convention. This is discussed briefly in “HP-UX Architecture Conventions” on page 39. You can find detailed information on both 32-bit and 64-bit calling conventions under the topic PA-RISC Architecture at URL: http://www.software.hp.com/STK/.

Table 2-7	Register Procedure Calling Conventions
		Register	Synonyms	Description
		%fr4	%farg0 %fret	Floating argument, return value
		%fr5	%farg1	Second floating argument
		%fr6	%farg2	Third floating argument
		%fr7	%farg3	Fourth floating argument
		%r2	%rp	Return link
		%r19	%t4	Fourth temporary register
		%r20	%t3	Third temporary register
		%r21	%t2	Second temporary register
		%r22	%t1	First temporary register
		%r23	%arg3	Argument word 3
		%r24	%arg2	Argument word 2
		%r25	%arg1	Argument word 1
		%r26	%arg0	Argument word 0
		%r27	%dp	Data pointer
		%r28	%ret0	Return value
		%r29	%ret1 %sl	Return value, static link
		%r30	%sp	Stack pointer
		%r31	%mrp	Millicode return link
		%sr1	%sret %sarg	Return value, argument

In addition, there is a special register mnemonic defined as %previous_sp, that allows access to the previous value of the stack pointer.

%previous_sp must be used in the position of a base register; it can be used only between .ENTER and .LEAVE pseudo-operations. %previous_sp is the same as %sp unless the current .PROC has a large

28 Chapter 2