How to debug a bootloader (syslinux on x86)

[anatolik]

I need to patch/compile syslinux on Linux Arch (BIOS+GPT partition). Unfortunately when I install my version of syslinux it fails to boot. It gives me black screen at very early stages. There is something wrong, but syslinux does not provide any useful information. I would like to debug the problem.

What is the best way to debug bootloaders? My gut feeling that there are 2 way:
- use serial port to connect to running machine and check the debug output
- use qemu/bosch and remote gdb debugger

I was not able to find any useful information about doing either way. Did anyone tried to do these thing? Could you share your experience/steps to reproduce?

Thanks for your reply in advance.

[Roman]

I need to patch/compile syslinux on Linux Arch (BIOS+GPT partition). Unfortunately when I install my version of syslinux it fails to boot. It gives me black screen at very early stages. There is something wrong, but syslinux does not provide any useful information. I would like to debug the problem.

What is the best way to debug bootloaders? My gut feeling that there are 2 way:
- use serial port to connect to running machine and check the debug output
- use qemu/bosch and remote gdb debugger

I was not able to find any useful information about doing either way. Did anyone tried to do these thing? Could you share your experience/steps to reproduce?

Thanks for your reply in advance.

Hi, you can also create break points with cli and hlt and test in QEMU. About using GDB with QEMU: http://wiki.qemu.org/Documentation/Debugging