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nolibcshell

This project is a minimal Linux shell written in C that is compiled without including libc.

Compiling

There are three options for building this project:

  1. An x86_64 binary using the make shell command.
  2. An x86 binary using the make shell32 command.
  3. An x86_64 binary made with a unity build (why not?) using the make unity command.

Design

The shell is implemented in shell.c along with a custom library that provides helpful functions needed by the shell.

The library is implemented in strings.{c,h} which contains helpful functions for interacting with "strings," heap.{c,h} which contains a simplistic heap implementation and malloc() and free() functions, and mylib.{c,h} which primarily contains the wrapper functions for making system-calls.

System-calls are implemented in $(ARCH)/syscall.h as in-line assembly macros. There are supported values for $(ARCH) are x86 and x86_64.

The entrypoint for the shell is written in assembly in $(ARCH)/entry.S. The entry.S file is necessary to provide the _start function and to provide argc, argv and envp to main().

Credit

An excellent heap implementation tutorial: https://danlulu.com/malloc-tutorial.