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StarkeBlog – Reverse Engineering MenuetOS 64 – Primary Boot Loader
Firmware and Hacking There are two types of boot systems in x86/x64 environments: UEFI and BIOS-based. UEFI provides a standard and reference implementation for the code that executes between the CPU being released from reset and the computer transferring execution to code stored on fixed media, such as hard disks and USB drives.
Before we begin reverse engineering the MenuetOS 64 primary bootloader, there is a small amount of prerequisite background that will help us in understanding how the PBL works. This makes sense, as the legacy grub implementation is also a primary bootloader for BIOS-based systems, performing many of the same functions as the MenuetOS 64 PBL. Likewise, if we have a debugger attach at this point and we send an interrupt signal by pressing CTRL+C at the gdb prompt, we will see that the CPU is in the tight loop that is the last instruction of the PBL:
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