Re: [PATCH] Use mmap for symbol tables

[Eirik Fuller <eirik@hackrat.com>]

> One important note: you bypassed symfile_relocate_debug_section.

The first time I read this I didn't fully understand it (I just hadn't
really read that code yet).  I think I understand it now.

I also saw comments near symfile_relocate_debug_section which suggest
that it won't be trivial to find a test case, contrary to my earlier
response.  UPS delivered my disk drive from NewEgg today, which means
I should have a PowerPC GNU/Linux system soon (the disk will soon be
the second disk in my G5).  I might still need to pay attention to
linker issues to fully explore this; I guess I'll find out soon.  :-)

Nonetheless I do have this revised patch.  On symbol tables I use it
seems to be equivalent to the one I sent earlier.  I'm not resending
the entire patch, just the part that affects gdb/dwarf2read.c

One assumption in this revised patch which I haven't fully validated
is that it makes sense to free the obstack_alloc'd buf if bfd_fetch
returns a non-NULL value.  I figure if symfile_relocate_debug_section
returns NULL, either there were no subsequent calls to obstack_alloc,
or nothing allocated by obstack_alloc after buf matters any more.  I'm
sure there's a cleaner way to approach this (which almost certainly
requires a bit more complication in the patch), but if the mmap calls
are eventually per-section in the BFD code (due to other complications
in the patch) instead of covering an entire file, this piece of the
patch will presumably look very different anyway.

> No, probably you should just bypass the mmap if the code in that
> function triggers.

I think this revised patch fits that description, by deferring the
call to bfd_fetch.

--- gdb/dwarf2read.c.orig	2006-01-17 14:30:29.000000000 -0800
+++ gdb/dwarf2read.c	2006-02-07 12:57:46.000000000 -0800
@@ -4958,6 +4958,13 @@
   if (retbuf != NULL)
     return retbuf;
 
+  retbuf = bfd_fetch(sectp->filepos, size, abfd);
+  if (retbuf != NULL)
+    {
+      obstack_free(&objfile->objfile_obstack, buf);
+      return retbuf;
+    }
+
   if (bfd_seek (abfd, sectp->filepos, SEEK_SET) != 0
       || bfd_bread (buf, size, abfd) != size)
     error (_("Dwarf Error: Can't read DWARF data from '%s'"),