Skip to content

Latest commit

 

History

History
44 lines (33 loc) · 1.62 KB

README.md

File metadata and controls

44 lines (33 loc) · 1.62 KB
Raw

dynamic-loader

A simple dynamic library loader for Linux capable of loading simple binaries using simple shared libraries.

Features

  • Actually readable codebase for a dynamic loader
  • Loads simple shared objects (no glibc or musl support*)
  • Calls initializers and finalizers
  • Performs relocations at load-time (no lazy loading supported yet)
  • Supports dlopen(), dlsym(), and dlclose()
  • no support for threads or TLS, though rudimentary thread-safety is supported in the loader

* glibc and musl provide their own dynamic library loader that they expect to be loaded with:

  • ld-linux-x86_64.so.2 (aka ld.so) for glibc
  • ld-musl-x86_64.so.1 (a symlink to musl's libc.so) for musl

Dependencies

  • libmusl.a and musl-gcc (arch: musl, debian: musl musl-tools)
  • elf.h (arch: part of base, debian: libelf-dev)

Building

  • cmake -B build
  • cd build
  • make
  • run build/loader/libloader.so or any of the binaries in build/tests/bin/

Resources

This loader was written mostly by using specifications from refspecs.linuxbase.org, mainly the ELF spec and the x86_64 processor supplement.

For some parts of the early loader startup code (mainly the code in crt/), I also read the source code of musl libc to get a better understanding of typical ways to handle early loader init. To understand ELF symbol hash tables, I used multiple sources, but this blog post on flagpenguin.me was most useful.