[Qemu-devel] Problems with gdbserver and debugging

[Andre Pech <apech@arastra.com>]

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Hi,

I'm running into problems using qemu to debug a kernel module. My host and
virtual machine are both x86 running Fedora Core 4. After insmoding the
module in the virtual machine, starting gdbserver, running gdb on the host
with the module sections loaded at the right place, and setting a breakpoint
in the module code, gdb does not always get notified when the code is
exectuted. After adding debugging statements to qemu, I've experienced the
following two different failure cases:

1) The breakpoint is set, but translate.c:gen_intermediate_code_internal is
not being called for the breakpoint address. If I understand things
correctly, this suggests that the translation block invalidation code which
is executed each time a breakpoint is set has a problem in it.

2) translate.c:gen_intermetiate_code_internal is called on the address where
the breakpoint is set, and gen_debug is called. However, gdb does not break
into the code. With DEBUG_GDB set, you can see that the gdbstub code isn't
doing anything in this case, so the gdb process i am running is never
notified that the breakpoint was hit.

Both of these cases occur frequently, but not every time. I can run gdb,
have it break correctly, kill gdb (after disabling the breakpoint and
continuing), then start gdb again and have it fail.

I'm going to keep trying to debug this, but I was hoping that someone might
have some insight into what is going on here. I have not upgraded to qemu
0.8.0 yet, but i couldn't find anything that suggested that this would fix
the problem. Has anyone else run into similar problems?

Thanks
Andre Pech

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