impossible to resolve symbols in same binary loaded twice with dlmopen

[Mathieu Lacage <mathieu.lacage@sophia.inria.fr>]

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hi,

A couple of months ago, I reported on the gdb mailing-list this issue:
http://sourceware.org/ml/gdb/2010-02/msg00027.html (the original report
mentionned a crash which happened with a different program loader but
the root cause of the problem is the same as the one mentionned here)
and tom tromey gave hints on how it could be fixed. It took me a while
to eventually put together a patch and a reduced testcase for this issue
but here it is in the bugzilla database:
http://sourceware.org/bugzilla/show_bug.cgi?id=11766

For convenience, this email contains the reduced testcase and patch
attached. Here is the associated ChangeLog entry:

2010-XX-XX Mathieu Lacage <mathieu.lacage@inria.fr>

        Fix PR/gdb 11766: gdb does not resolve correctly symbols in
binaries loaded twice with dlmopen

        Because the name of an inferior binary present in the linkmap is
not sufficient for the test of uniqueness, of an entry in the list of
objfiles, we ensure uniqueness with an extra equality condition, the
addr_low member of the binary.

        * gdb/objfiles.h: add addr_low member variable
        * gdb/solib.c (solib_read_symbols): check for addr_low in
equality test for objfile, initialize addr_low if needed.


I really care about fixing this issue because it hits me and a lot of my
users and asking them to recompile gdb with a patch is not fun in the
long run. I am looking forward to fix this upstream so, please, let me
know what I can do to help with the resolution of this issue.

Mathieu
-- 
Mathieu Lacage <mathieu.lacage@sophia.inria.fr>
Tel: +33 4 9238 5056

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? objdir
? patch
Index: gdb/objfiles.h
===================================================================
RCS file: /cvs/src/src/gdb/objfiles.h,v
retrieving revision 1.72
diff -c -p -r1.72 objfiles.h
*** gdb/objfiles.h	14 Apr 2010 17:26:11 -0000	1.72
--- gdb/objfiles.h	7 Jul 2010 18:35:38 -0000
*************** struct objfile
*** 193,198 ****
--- 193,200 ----
  
      char *name;
  
+     CORE_ADDR addr_low;
+ 
      /* Some flag bits for this objfile. */
  
      unsigned short flags;
Index: gdb/solib.c
===================================================================
RCS file: /cvs/src/src/gdb/solib.c,v
retrieving revision 1.140
diff -c -p -r1.140 solib.c
*** gdb/solib.c	16 May 2010 23:49:58 -0000	1.140
--- gdb/solib.c	7 Jul 2010 18:35:39 -0000
*************** solib_read_symbols (struct so_list *so, 
*** 634,644 ****
        TRY_CATCH (e, RETURN_MASK_ERROR)
  	{
  	  struct section_addr_info *sap;
- 
  	  /* Have we already loaded this shared object?  */
  	  ALL_OBJFILES (so->objfile)
  	    {
! 	      if (strcmp (so->objfile->name, so->so_name) == 0)
  		break;
  	    }
  	  if (so->objfile != NULL)
--- 634,644 ----
        TRY_CATCH (e, RETURN_MASK_ERROR)
  	{
  	  struct section_addr_info *sap;
  	  /* Have we already loaded this shared object?  */
  	  ALL_OBJFILES (so->objfile)
  	    {
! 	      if (strcmp (so->objfile->name, so->so_name) == 0
! 		  && so->objfile->addr_low == so->addr_low)
  		break;
  	    }
  	  if (so->objfile != NULL)
*************** solib_read_symbols (struct so_list *so, 
*** 648,653 ****
--- 648,654 ----
  							    so->sections_end);
  	  so->objfile = symbol_file_add_from_bfd (so->abfd,
  						  flags, sap, OBJF_SHARED);
+ 	  so->objfile->addr_low = so->addr_low;
  	  free_section_addr_info (sap);
  	}