gdb/glibc-tdep.c

   1 /* Target-dependent code for the GNU C Library (glibc).
   2
   3    Copyright 2002, 2003 Free Software Foundation, Inc.
   4
   5    This file is part of GDB.
   6
   7    This program is free software; you can redistribute it and/or modify
   8    it under the terms of the GNU General Public License as published by
   9    the Free Software Foundation; either version 2 of the License, or
  10    (at your option) any later version.
  11
  12    This program is distributed in the hope that it will be useful,
  13    but WITHOUT ANY WARRANTY; without even the implied warranty of
  14    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15    GNU General Public License for more details.
  16
  17    You should have received a copy of the GNU General Public License
  18    along with this program; if not, write to the Free Software
  19    Foundation, Inc., 59 Temple Place - Suite 330,
  20    Boston, MA 02111-1307, USA.  */
  21
  22 #include "defs.h"
  23 #include "frame.h"
  24 #include "symtab.h"
  25 #include "symfile.h"
  26 #include "objfiles.h"
  27
  28 #include "glibc-tdep.h"
  29
  30 /* Calling functions in shared libraries.  */
  31
  32 /* Find the minimal symbol named NAME, and return both the minsym
  33    struct and its objfile.  This probably ought to be in minsym.c, but
  34    everything there is trying to deal with things like C++ and
  35    SOFUN_ADDRESS_MAYBE_TURQUOISE, ...  Since this is so simple, it may
  36    be considered too special-purpose for general consumption.  */
  37
  38 static struct minimal_symbol *
  39 find_minsym_and_objfile (char *name, struct objfile **objfile_p)
  40 {
  41   struct objfile *objfile;
  42
  43   ALL_OBJFILES (objfile)
  44     {
  45       struct minimal_symbol *msym;
  46
  47       ALL_OBJFILE_MSYMBOLS (objfile, msym)
  48         {
  49           if (SYMBOL_LINKAGE_NAME (msym)
  50               && strcmp (SYMBOL_LINKAGE_NAME (msym), name) == 0)
  51             {
  52               *objfile_p = objfile;
  53               return msym;
  54             }
  55         }
  56     }
  57
  58   return 0;
  59 }
  60
  61 /* See the comments for SKIP_SOLIB_RESOLVER at the top of infrun.c.
  62    This function:
  63    1) decides whether a PLT has sent us into the linker to resolve
  64       a function reference, and
  65    2) if so, tells us where to set a temporary breakpoint that will
  66       trigger when the dynamic linker is done.  */
  67
  68 CORE_ADDR
  69 glibc_skip_solib_resolver (struct gdbarch *gdbarch, CORE_ADDR pc)
  70 {
  71   /* The GNU dynamic linker is part of the GNU C library, and is used
  72      by all GNU systems (GNU/Hurd, GNU/Linux).  An unresolved PLT
  73      entry points to "_dl_runtime_resolve", which calls "fixup" to
  74      patch the PLT, and then passes control to the function.
  75
  76      We look for the symbol `_dl_runtime_resolve', and find `fixup' in
  77      the same objfile.  If we are at the entry point of `fixup', then
  78      we set a breakpoint at the return address (at the top of the
  79      stack), and continue.
  80
  81      It's kind of gross to do all these checks every time we're
  82      called, since they don't change once the executable has gotten
  83      started.  But this is only a temporary hack --- upcoming versions
  84      of GNU/Linux will provide a portable, efficient interface for
  85      debugging programs that use shared libraries.  */
  86
  87   struct objfile *objfile;
  88   struct minimal_symbol *resolver
  89     = find_minsym_and_objfile ("_dl_runtime_resolve", &objfile);
  90
  91   if (resolver)
  92     {
  93       struct minimal_symbol *fixup
  94         = lookup_minimal_symbol ("fixup", NULL, objfile);
  95
  96       if (fixup && SYMBOL_VALUE_ADDRESS (fixup) == pc)
  97         return frame_pc_unwind (get_current_frame ());
  98     }
  99
 100   return 0;
 101 }