Debug Linux kernel pre-decompression stage

Posted by Shawn J. Goff on Stack Overflow See other posts from Stack Overflow or by Shawn J. Goff
Published on 2012-03-05T23:40:39Z Indexed on 2012/10/12 3:37 UTC
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Filed under:

gdb

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embedded

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linux-kernel

I am trying to use GDB to debug a Linux kernel zImage before it is decompressed. The kernel is running on an ARM target and I have a JTAG debugger connected to it with a GDB server stub. The target has to load a boot loader. The boot loader reads the kernel image from flash and puts it in RAM at 0x20008000, then branches to that location.

I have started GDB and connected to the remote target, then I use GDB's add-symbol-file command like so:

add-symbol-file arch/arm/boot/compressed/vmlinux 0x20008000 -readnow

When I set a breakpoint for that address, it does trap at the correct place - right when it branches to the kernel. However, GDB shows the wrong line from the source of arch/arm/boot/compressed/head.S. It's 4 lines behind. How can I fix this?

I also have tried adding the -s section addr option to add-symbol-file with -s .start 0x20008000; this results in exactly the same problem.

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