Fwd: Solibs and objfile BFD ownership

[Paul Pluzhnikov <ppluzhnikov at google dot com>]

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---------- Forwarded message ----------
From: Paul Pluzhnikov <ppluzhnikov@google.com>
Date: Mon, Aug 17, 2009 at 3:44 PM
Subject: Re: Solibs and objfile BFD ownership
To: Paul Pluzhnikov <ppluzhnikov@google.com>, tromey@redhat.com,
gdb@sourceware.org


On Tue, Aug 4, 2009 at 11:47 AM, Paul Pluzhnikov<ppluzhnikov@google.com> wrote:

> So committed. Thanks,

I seem to have hit a rough patch with my patches :-(

The BFD refcounting patch from 2009-08-04 causes GDB to crash when I attach
to a process with many solibs, then (while GDB is reading solib symbols)
change my mind about attaching and hit Control-C, then 'run'.

This is happening because in symbol_add_stub refcount may not be set:

? so->objfile = symbol_file_add_from_bfd (so->abfd, flags, sap, OBJF_SHARED);

---> QUIT could be executed deep inside symbol_file_add_from_bfd, and
---> bfd_userdata below is never set.

? p_refcount = xmalloc (sizeof (*p_refcount));
? *p_refcount = 2; ?/* Both solib and objfile refer to this abfd. ?*/
? bfd_usrdata (so->abfd) = p_refcount;

Later, we re-enter symbol_add_stub, and this:

? ALL_OBJFILES (so->objfile)
? ? {
? ? ? if (strcmp (so->objfile->name, so->so_name) == 0)
? ? ? ? return;

re-connects the so with the objfile, but never sets the bfd_usrdata.

Later still (during execution of 'run'), we go through clear_solib and
objfile_purge_solibs, and the latter crashes trying to bfd_close the abfd
which has already been bfd_close()d by the former.

Here is a proposed patch. Tested on Linux/x86_64 with no new failures.

Thanks,
--
Paul Pluzhnikov

2009-08-17 ?Paul Pluzhnikov ?<ppluzhnikov@google.com>

? ? ? ?* solib.c (set_ref_count): New function.
? ? ? ?(symbol_add_stub): Call it.

Attachment: gdb-bfd-ownership-20090817.txt
Description: Text document