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How to get file descriptor from abfd?
- From: Paul Pluzhnikov <ppluzhnikov at google dot com>
- To: binutils at sourceware dot org
- Cc: Tom Tromey <tromey at redhat dot com>, gdb-patches ml <gdb-patches at sourceware dot org>
- Date: Sun, 31 May 2009 10:56:34 -0700
- Subject: How to get file descriptor from abfd?
Greetings,
Currently GDB allocates memory and does a bfd_read() on dwarf debug sections.
This causes GDB to be significantly slower on low-memory machines than
it has to be, and I have a patch to fix this by directly mmap()ing the
debug sections instead:
http://sourceware.org/ml/gdb-patches/2009-05/txt00023.txt
In that patch, I do:
+ caddr_t retbuf = mmap (0, map_length, PROT_READ, MAP_PRIVATE,
+ fileno ((FILE *)abfd->iostream),
+ pg_offset);
and this cast of abfd->iostream has been flagged as possibly un-kosher.
What is the proper way to get access to the underlying file descriptor
for a given abfd (if there is one)?
If there isn't a way, should there be?
I would have used bfd_get_file_window(), but it's only compiled in
when --use-mmap was given to bfd/configure.
Is there a way to turn that on for GDB?
The bfd_get_file_window() performs above cast, after checking for:
(abfd->flags & BFD_IN_MEMORY) == 0)
and later
if (abfd->iostream == NULL
&& (abfd->iovec == NULL
|| abfd->iovec->bseek (abfd, offset, SEEK_SET) != 0))
The last 3 conditions can not be true in gdb/dwarf2read.c because we just
performed bfd_seek and bfd_bread on abfd.
Looks like BFD_IN_MEMORY could be set though.
Is it ok to do this:
if ((abfd->flags & BFD_IN_MEMORY) == 0) ...
in gdb/dwarf2read.c?
Thanks,
--
Paul Pluzhnikov