Question

I am connecting gdb to a virtual machine’s kernel and trying to debug the kernel module. I am able to connect to the virtual machine. I have symbol information for kernel code, and can step through kernel code just fine.

When I add the symbol file for my kernel module (whether I do this before or after remote connection, incidentally), I am able to list <function_name> information about the function, until I set a breakpoint; after that:

(gdb) b function_name
Breakpoint 1 at 0xffffffffa01d0074 (3 locations)
(gdb) list function_name
No line number known for function_name.

Additional information:

• Both host and guest are Fedora 16 64-bit.
• The kernel I am debugging is 3.0.8 – note that this kernel worked fine on a prior 32-bit setup with a different environment and remote-connection setup.
• I have tried this with gdb 7.2 and 7.3.50.

Any ideas on whats wrong? It would help if I even knew for certain whether the problem was my kernel, kernel module compilation, the connection, or gdb.

Update: With gdb 7.1, I get the following:

...
(gdb) b function_name
/gdb/breakpoint.c:7903: internal-error: expand_line_sal_maybe: Assertion `found' failed.
A problem internal to GDB has been detected,
further debugging may prove unreliable.

What does that mean?

Answer 1

A partial answer:

With gdb 7.1, recompiling the kernel and kernel module with -gdwarf-2, and the module with -O0 seems to have done the trick. I’m not sure which it is or why yet.