The Mach Object (Mach-O) is the binary format used on Apple’s operating systems for executables, libraries, and object code. It was created for the Mach kernel (hence the name) and introduced in NeXTSTEP, the predecessor to macOS, as a replacement for the a.out format. Mach-O’s design supports multiple architectures (via universal binaries), and contains metadata via load commands. In this post, we’ll explore Mach-O’s layout and history. Then, we will examine how macs use Mach-O for code signing...