# Libdwarf Internals Introduction

The library is organized into a conceptual LeftHandSide (LHS, DWARF related) and a conceptual RightHandSide (RHS,object file related). All the functions in the API are functions in the LHS, and the LHS knows nothing about the actual object file.

The RHS provides a small number of function pointers and the LHS uses those functions to access any object file being read. The RHS knows nothing about the functions in the LHS.

There are three RHS code blocks. An Elf, a PE, and a MacOS block (reflected in header and source names in libdwarf). The structure of simple Elf objects is reflected in the function pointers each of the three provide. The PE and MacOS blocks hide the differences from Elf from the LHS.

All the code blocks are available at runtime, there is no selecting at library-build time.

# Libdwarf Internals Overview

## Initialization

Any one of the functions

dwarfinitpath(), dwarfinitpatha(), dwarfinitpathdl(), dwarfinitpathdla(), or dwarfinitb() may be used.

dwarfinitpathdla() is the most general, but for most objects dwarfinitpath() suffices. Other flavors allow more control in looking to find an object file containing actual DWARF when given a path to an object without DWARF data (compilers provide hints to libdwarf to help find the DWARF-containing object).

When initialization is complete both the LHS DWARF data and the RHS object-specific data have arrays of sections. These are defined as, and must be, one-to-one identical in terms of numbering so index B in one and index B in the other refer to the same actual object section. This is crucial as section index is what connects LHS data and RHS data.

## Reading DWARF via the API.

The API functions work on any object, regardless of ABI and all functions account for endianness.

## dwarf_finish()

Finish by calling dwarf_finish(), releasing all memory allocations and making any pointers to libdwarf data in your application memory stale and unusable.

Before release 0.12.0 the functions

dwarfdestructelfnlaccess(dbg->deobjfile), dwarfdestructmachoaccess(dbg->deobjfile), dwarfdestructpeaccess(dbg->deobjfile).

were visible to the entire library, but as of 0.12.0 there is a new function pointer in DwarfObjAccessMethodsa: om_finish(), and those three are declared static, invisible to the LHS.

# The Special Case

If there is no object file to read (such as with just-in-time DWARF creation)
an extra initialization call (dwarfobjinit()) lets one invent RHS code that behaves as if there was a file and present the DWARF data to the LHS in the same was as for the standard object files.

Initialize by calling dwarfobjectinit_b().

Finish by calling dwarfobjectfinish().

See src/bin/dwarfexample/jitreader.c