Debugging kernel very early in boot process

Question

I'm porting the Linux kernel to a new platform and I'm having a little trouble debugging.

The kernel seems to hang after Uncompressing Linux... done, booting the kernel. is printed to UART. I've enabled early printk but it still doesn't print anything new so I'm assuming it's hanging very early in the boot process.

The platform I'm porting to does have a LED I can use to try and pinpoint where it is actually hanging. The problem with this is that it's messy and I don't know when the MMU is going to be switched on so I can't reliably access the port.

Are there other ways to try and pinpoint where the kernel is hanging?

Answer 1

The MMU is turned on in the kernel bootstrap (head.S), so just add some LED poking around there. See this slightly outdated file for overview of the boot sequence on ARM Linux.