Reference Guide

48 Chapter 3

HP-UX Architecture Conventions

Compiler Conventions

the return link either in a register or on the stack. Also, it can determine

the previous stack pointer by subtracting the current procedure's stack

frame size.

The Assembler requires that you follow programming conventions to

generate unwind descriptors. The beginning and end of each procedure

must be noted with the .PROC and .PROCEND directives. The .CALLINFO

directive supplies additional information about the procedure, including

the stack frame size. The Assembler passes this information to the

linker, which creates the unwind descriptor. It can also generate the

standard entry and exit code to create and destroy the stack frame, save

and restore the return link (if necessary), and save and restore any

necessary registers. These code sequences are generated at the points

indicated by the .ENTER and .LEAVE pseudo-operations. For a more

thorough discussion of programming conventions, refer to the 64-bit

Runtime Architecture for PA-RISC 2.0, at URL:

http://www.software.hp.com/STK/.

Arguments to procedures are loaded into general registers 26, 25, 24,

and 23; these registers are named, respectively, %arg0, %arg1, %arg2,

and %arg3. If more than four words of arguments are required, the

remaining arguments are stored in the caller's stack frame in the

variable argument list. The return value should be returned in general

the low-order bits of a double-word return value, while %ret0 contains

the high order bits. In addition to the argument and return registers, the

procedure can use registers 19 through 22 and registers 1 and 31 as

scratch registers. Any other general registers must be saved before use

at entry and restored before exit.

Chapter 4, “Assembler Directives and Pseudo-Operations,” on page 53

contains detailed descriptions of the Assembler directives described

above. For a more thorough discussion of the procedure calling

conventions, refer to the topic PA-RISC Architecture at URL:

http://www.software.hp.com/STK/.

In order for an assembly language procedure to be callable from another

language or another assembly language module, the name of the

procedure must be exported. The .EXPORT directive does this. It also

allows you to declare the symbol type. For procedure entry points, the

symbol type should be ENTRY.

The Assembler and linker treat all symbols as case-sensitive, while some

compilers do not. By convention, compilers that are case-insensitive

uniformly convert all exported names to lower case. For example, it is