Elf

Elf Encoder/Decoder

This directory contains code for encoding and decoding of little-endian Elf executables. The C++ implementation assumes that the host system is also little-endian.

The implementation is slightly more comprehensive than what is needed by Cwerg and might be useful by itself. Shared executables and dynamic libraries have not been tested as they are out of scope for the project. The code is a bit opinionated about the format of the executable but should works for many executables found in the wild.

Expected format

    [EhdrIdent]     16 bytes
    [Ehdr]          (32 or 64 bit version)
    [Phdr]+         (32 or 64 bit version)
    [Section Data]+ (mapped data precedes unmapped data)
    [Shdr]+         (32 or 64 bit version)

Concepts

Symbol (Wraps Elf Symbol)

TBD

Reloc (Wraps Elf Relocation)

TBD

Section (Wraps Elf Section)

A Section consists of an Elf Shdr and the corresponding data.

Segment (Wraps Elf Segment)

A Segment consists of an Elf Phdr and a list of Sections whose address range falls within the Segment. Segments can be primary or auxiliary. If a Section belongs to multiple Segments at most one of them can be primary. A special pseude Segment which is always comes last contains all the unmapped Sections. This Segment is not reflected as a Phdr in the Elf executable.

API

gen_elf_test.py and gen_elf_test.cc show how to use this library to generated simple executables for A32, A64 and X64.

Executable

An Executable consists of an Elf Ehdr and a list of Segments.