[Crash-utility] Re: Fix for source line numbers for x86_64 modules

[Wright, John (ALPS, Fort Collins)]

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.

-- 
+----------------------------------------------------------+
| John Wright <john.wright at hp.com>                         |
| HP Mission Critical OS Enablement & Solution Test (MOST) |
+----------------------------------------------------------+
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