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Re: [PATCH] Use mmap for symbol tables
- From: Eirik Fuller <eirik at hackrat dot com>
- To: Daniel Jacobowitz <drow at false dot org>
- Cc: gdb-patches at sourceware dot org
- Date: Tue, 7 Feb 2006 14:05:34 -0800 (PST)
- Subject: Re: [PATCH] Use mmap for symbol tables
- References: <20060131022330.GA24934@nevyn.them.org> <20060131033837.GA26401@nevyn.them.org>
> 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'"),