Pavel Cahyna <pavel.cahyna@st.cuni.cz> writes:

> Please use "bt/l" in ddb next time you repeat this bug. I saw that
> sometimes (maybe always?) one frame is missed by gdb, but shows in ddb
> when the kernel panics with uvm_fault (which is usually a symptom of a
> NULL-pointer dereference). See for example PR kern/28669:

The trouble here is that GDB's stack-walking code doesn't know that
trap frames are different from ordinary stack frames. DDB does know
this. The Right Thing would be to manually add some DWARF-2
annotations to the assembly code that handles trap so that GDB could
understand how to find the real next frame.

        - Nathan