I've been writing a lot of assembly over recent months (the runtime routines for a lisp compiler, and of course debugging the generated assembly my compiler emits itself).

Mostly all I do is run a backtrace from the segfaults, and otherwise single-step through the code to verify my assumptions.

GDB has sufficed pretty well, though I admit I spent a long time writing the stop&copy garbage collector, and tracing through it trying to understand why I was getting segfaults.

I'm sure there are better tools, but for simple debugging it was sufficient.