Ftrace, KASLR and gdb

[alexandre.ferrieux@orange.com]

Hi,

Ftrace is a jewel to dig into the kernel, be it for troubleshooting, perf tuning 
or just understanding.
But when one needs to disassemble the running kernel (eg to move kprobes around 
in a function, in order to understand a given code path), KASLR makes it 
impossible for gdb to get useful symbol addresses, even with a debug image.
That said, /proc/kallsyms always gives the accurate, present symbol addresses. 
But, to my knowledge, gdb isn't able to import /proc/kallsyms as a symbol table.
To circumvent this, I've written a small userland tool, usling libbfd, that 
creates an ELF file out of /proc/kallsyms. Passing this ELF file to gdb instead 
of "vmlinux", and /proc/kcore as core, then allows for a perfect gdb session on 
the running kernel. Of course this ELF file is only valid until the next reboot, 
but that's okay as its creation is fast.

Now, my question: did I miss an alternative ?

In other words, is there some kind of "kallsyms plug-in" for gdb somewhere ?
Or, taking the problem from the other side, some kernel module exposing a 
"/proc/kallsyms.elf" or similar, for direct consumption by gdb ?
Or another method, that people routinely use for the same purpose ?

Thanks in advance,

-Alex




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