Skip to main content

Home

info

The content is written with a focus on macOS as it is the OS used at 42 Mulhouse, it should mostly work the same on Linux.

The goal of this website is to provide an introduction to the methods and tools you can use to debug your program during the common core of 42 and beyond.

You will not find in-depth information on the inner working of the tools or their advanced options, for that dig on your own and RTFM.

The tools presented here are very useful, but they are not magic. They are themselves subject to bugs and cannot be trusted at 100%. They are not a replacement for the understanding of your code and the machine they are running on.

I would also suggest spending more time understanding the methods to debug a program than the tools to do so. They will be relevant with most of the programming languages you will encounter.

This project is a work in progress. You can take part in its improvement by opening issues or sending pull request to its repository.

Setup​

Before continuing, here are some preliminary steps you should do to set up your machine.

Homebrew​

Homebrew is a package manager, you will use it to install, manage and update software on your machine.

Since you do not have the admin rights on 42's computers and the disk space is limited I suggest you to use this script to install it in the goinfre of the machine you are using.

https://github.com/omimouni/42homebrew

$ curl -fsSL https://raw.githubusercontent.com/omimouni/42homebrew/master/install-goinfre.sh | zsh

LLVM​

LLVM is an open source compiler and toolchain that include Clang. By default, macOS ship with an old version of it, you can use Homebrew to install the latest version, this will give you access to better tooling, performance and error handling.

$ brew install LLVM

To be able to use it you will have to update the PATH variable. In your .zshrc add the following line:

export PATH=~/goinfre/.brew/opt/llvm/bin:$PATH

When you type clang in your terminal you will use the latest version, the one you just installed. You can still use cc to access the default version (required for your projects).

Debug information​

To have more accurate information with the tools, you must generate the debug information while compiling your program.

To do that, add the -g flag when compiling.

This will add the debug information to the output file or in a .dSYM file for macOS.

As it does not load these informations when running normally, your program performance will not be affected.

More flags are available to output these informations, such as -g3, -ggdb, you can find more details in your compiler documentation.

Example​

Without debug information:

==41461==The signal is caused by a WRITE memory access.
==41461==Hint: address points to the zero page.
    #0 0x10d3a4f4c in main+0x5c (a.out:x86_64+0x100003f4c)
    #1 0x7fff72f3fcc8 in start+0x0 (libdyld.dylib:x86_64+0x1acc8)

With debug information:

==41523==The signal is caused by a WRITE memory access.
==41523==Hint: address points to the zero page.
    #0 0x106f73f4c in main test.c:7
    #1 0x7fff72f3fcc8 in start+0x0 (libdyld.dylib:x86_64+0x1acc8)