----- "John Wright (ALPS, Fort Collins)" <john.wright@xxxxxx> wrote: > On Wed, Sep 16, 2009 at 04:44:32PM -0600, Bob Montgomery wrote: > > John and I think that this code in gdb searches things too many times, > > particularly with this patch, but it's a start since it seems to fix the > > problem. > > I'm attaching a new version of the patch, that performs way better when > disassembling functions that live in the kernel. (Bob found that the > original patch made crash disassemble in-kernel functions at least 3 > times slower, but that number will be larger depending on how close the > symbol table the function lives in is to the head of the psymtabs list. > Module disassembly speed wasn't changed much at all.) With this updated > patch, we found the performance penalty of "dis -l" to be marginal. > > The problem with the original patch is that once the address we want is > found in a symbol table, it then looks through the rest of the symbol > tables in that objfile for a better match. The original code would then > return the best pst out of that objfile (and never get the next pst > from ALL_PSYMTABS), but we want to go through the rest of the objfiles > just in case, so I moved the return statement outside of the > ALL_PSYMTABS loop. But the next pst from ALL_PSYMTABS will not be from > a new objfile - so we would wind up traversing the list (minus one > element) again, and again, and again... > > The new patch removes the inner list traversal, and just takes advantage > of the fact that we already iterate through every pst via > ALL_PSYMTABS. Hi John Yeah, this second patch works much better. In fact, I only noticed today -- using your first patch -- that if I pick a text address in the kernel proper that is very close to "_etext", the disassembly never returns from gdb. For example, on an 2.6.29.4-167.fc11 kernel, if I do this with the first patch applied: crash> sym -l ... [ snip ] ... ffffffff813afac4 (T) register_kprobes ffffffff813afb26 (T) recycle_rp_inst ffffffff813afbbb (T) kprobe_flush_task ffffffff813afc75 (t) collect_one_slot ffffffff813afd18 (t) collect_garbage_slots ffffffff813afda9 (T) free_insn_slot ffffffff813afe4d (T) get_insn_slot ffffffff813aff85 (T) __kprobes_text_end ffffffff813b02ec (t) bad_iret ffffffff813b0313 (t) bad_gs ffffffff813b2250 (T) bad_from_user ffffffff813b2256 (t) bad_to_user ffffffff813b2830 (T) __start_notes ffffffff813b2830 (T) _etext ... crash> dis -l register_kprobes < never returns > With your new patch (and unpatched for that matter) it works OK. Dave -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
