Re: [PATCH] Use mmap for symbol tables

[Michael Snyder <msnyder@redhat.com>]

> I'm just concerned about wasting address space.  People these days do
> have awfully big programs.  There are executables out there in the
> gigabytes (cue lurkers to share their horror stories).
> 

<snrk> Hmm?  Oh!  Um...

Yeah, you're right, Jim.  I've got users who have symbol files
with over a gigabyte of debug info.

Eirik, how about making this a user-specified option,
from the command line?  Seems like that would facilitate
performance testing anyways... besides helping on platforms
that don't have mmap.

I noticed a side thread about gdb "scanning the symbol info linearly"
on the first pass, and my thought on THAT was... what makes you think
it's linear?  With stabs it sure as hell isn't...

And another aside -- when one of my users with the gigabyte symtabs
tries to debug on a machine without enough physical memory, gdb
thrashes (naturally) -- but it thrashes BAD.  For all practical
purposes, the initial symbol scan never terminates.  That also
makes me doubt that the scan is linear.

One final ps -- this has been done before!  It was put in,
and it was taken out again.  One wonders if there was a reason
for taking it out.  A brief glance at Changelogs suggests that
it was put in in 1992, and removed again in 1996.  Hmm, here's
one that's poignant...

Wed Jan 31 13:34:52 1996  Fred Fish  <fnf@cygnus.com>

         * config/i386/xm-linux.h (MMAP_BASE_ADDRESS, MMAP_INCREMENT):
         Define to what should be reasonable values.  However, apparently
         a bug in linux mmap prevents mapped symbol tables from working.