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DWARF for the LoongArch™ Architecture

Abstract

This document describes the use of the DWARF debugging information format in the Application Binary Interface (ABI) for the LoongArch architecture.

Keywords

LoongArch, DWARF, Stack frame, CFA, CIE

Version History

Version Description

20230425

initial version.

Overview

The DWARF debugging format for LoongArch uses DWARF Standard [dwarfstd]. This specification only describes LoongArch-specific definitions.

Terms and Abbreviations

DWARF
Debugging With Attributed Record Formats.

LoongArch-specific DWARF Definitions

DWARF Register Numbers

DWARF Standard suggests that the mapping from a DWARF register name to a target register number should be defined by the ABI for the target architecture. DWARF register names are encoded as unsigned LEB128 integers.

The table below lists the mapping from DWARF register numbers to LoongArch64 registers.

Table 1. Mapping from DWARF register numbers to LoongArch64 registers
DWARF Register Number LoongArch64 Register Name Description

0 - 31

$r0 - $r31

General-purpose Register

32 - 63

$f0 - $f31

Floating-point Register

64 -

Reserved for future standard extensions

CFA (Canonical Frame Address)

The term Canonical Frame Address (CFA) is defined in DWARF Debugging Information Format Version 5 [dwarf5], §6.4 Call Frame Information.

This ABI adopts the typical definition of CFA given there:

the CFA is defined to be the value of the stack pointer at the call site in the
previous frame (which may be different from its value on entry to the current frame).

The position of CFA in frame structure of LoongArch is shown below:

         |                |
         | previous frame |
         |________________|
CFA----->|________________|<------ previous sp
         |_______ra_______|
         |_______fp_______|
         |                |
         | current frame  |
         |________________|
         |________________|<------ current sp

CIE (Common Information Entry)

The $r1 register is used to store the return address of the function, and the value of the return address register field in CIE structure is 1.

The default CFA register at the function entry is $r3, and initial_instructions field in CIE structure can define 3 as the default CFA register.

Call frame instructions

Using the existing definitions in DWARF Standard.

DWARF expression operations

Using the existing definitions in DWARF Standard.

References