[uml-devel] Using GDB in debugging UML kernel (2.6)

[Kristian Slavov <kristian.slavov@iki.fi>]

Hi,

I'm trying to debug my kernel code with UML and have run into couple of 
troubles. My host kernel is 2.6.3 patched with host-skas3-2.6.3-v1, the UML 
kernel is 2.6.3 with uml-patch-2.6.3-rc2-1. Both systems run Debian testing (sarge).

* GDB 5.3 with GCC 2.95

GDB does not recognize most of the structures. For example, try typing 'info 
types xfrm_state' (requires IPv6 + IPsec stuff compiled in kernel).
GDB will list many files. Some of them will show 'struct xfrm_state', most of 
them 'struct unknown'.
If I have a breakpoint in one of those file (that don't recognize the structure) 
I can't print the structure. I've tried 'print {struct xfrm_state *}variable' 
etc... but still nothing.
I don't really like to dump memory and try to interpret the structures manually.

* GDB 5.3 with GCC 3.3.3

info types xfrm_state shows the same files as above, but all of them now 
recognize the xfrm_state. The problem in this case is that GDB will only show me
one frame in the backtrace :( Not really useful having breakpoint in panic().

Actually I've exerienced this same behaviour with GCC-2.95 too. I changed -g to 
-ggdb in Linux makefiles. Perhaps GCC-3.3's -g is equal to GCC-2.95's -ggdb?

* GDB 6.0 with GCC 2.95 or 3.3.3

UML kernel does not send SIGTRAP at the beginning, or GDB ignores it. I checked 
info signal and the SIGTRAP's actions were 'stop, print, don't pass'. This is 
the same in both GDBs.

Now the actual question :)
What kind of setups do you use to debug UML? Do you have some ideas/suggestions 
to help me?

TIA
-- 
Kristian Slavov


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