Skeleton for building a ELF loader

Introduction

This project contains a skeleton for building an ELF binary on-demand loader in Linux. The loader will provide two methods, defined in the loader.h header:

• int so_init_loader(void); - initializes the on-demand loader
• int so_execute(char *path, char *argv[]); - executes the binary located in path with the required argv arguments.

Content

The project contains of three components, each of them in its own directory:

• loader - a dynamic library that can be used to run ELF binaries. It consists of the following files:
  • exec_parser.c - Implements an ELF binary parser.
  • exec_parser.h - The header exposed by the ELF parser.
  • loader.h - The interface of the loader, described in the Introduction section.
  • loader.c - This is where the loader should be implemented.
  • debug.h - header for the dprintf function that can be used for logging and debugging.
• exec - a program that uses the libso_loader.so library to run an ELF binary received as argument.
• test_prog - an ELF binary used to test the loader implementation.

There project also contains 2 makefiles:

• Makefile - builds the libso_loader.so library from the loader directory
• Makefile.example - builds the so_exec and so_test_prog binaries from the exec and test_prog directories that can be used to test the loader.

Usage Build the loader:

make

This should generate the libso_loader.so library. Next, build the example:

make -f Makefile.example

This should generate the so_exec and so_test_prog used for the test:

LD_LIBRARY_PATH=. ./so_exec so_test_prog

NOTE: the skeleton does not have the loader implemented, thus when running the command above, your program will crash!

Notes

This skeleton is provided by the Operating System team from the University Politehnica of Bucharest to their students to help them complete their Executable Loader assignment.