elf/dl-debug.c

   1 /* Communicate dynamic linker state to the debugger at runtime.
   2    Copyright (C) 1996-2023 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4
   5    The GNU C Library is free software; you can redistribute it and/or
   6    modify it under the terms of the GNU Lesser General Public
   7    License as published by the Free Software Foundation; either
   8    version 2.1 of the License, or (at your option) any later version.
   9
  10    The GNU C Library is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  13    Lesser General Public License for more details.
  14
  15    You should have received a copy of the GNU Lesser General Public
  16    License along with the GNU C Library; if not, see
  17    <https://www.gnu.org/licenses/>.  */
  18
  19 #include <ldsodefs.h>
  20
  21
  22 /* These are the members in the public `struct link_map' type.
  23    Sanity check that the internal type and the public type match.  */
  24 #define VERIFY_MEMBER(name) \
  25   (offsetof (struct link_map_public, name) == offsetof (struct link_map, name))
  26 extern const int verify_link_map_members[(VERIFY_MEMBER (l_addr)
  27                                           && VERIFY_MEMBER (l_name)
  28                                           && VERIFY_MEMBER (l_ld)
  29                                           && VERIFY_MEMBER (l_next)
  30                                           && VERIFY_MEMBER (l_prev))
  31                                          ? 1 : -1];
  32
  33 /* Update the `r_map' member and return the address of `struct r_debug'
  34    of the namespace NS. */
  35
  36 struct r_debug *
  37 _dl_debug_update (Lmid_t ns)
  38 {
  39   struct r_debug_extended *r;
  40   if (ns == LM_ID_BASE)
  41     r = &_r_debug_extended;
  42   else
  43     r = &GL(dl_ns)[ns]._ns_debug;
  44   if (r->base.r_map == NULL)
  45     atomic_store_release (&r->base.r_map,
  46                           (void *) GL(dl_ns)[ns]._ns_loaded);
  47   return &r->base;
  48 }
  49
  50 /* Initialize _r_debug_extended for the namespace NS.  LDBASE is the
  51    run-time load address of the dynamic linker, to be put in
  52    _r_debug_extended.r_ldbase.  Return the address of _r_debug.  */
  53
  54 struct r_debug *
  55 _dl_debug_initialize (ElfW(Addr) ldbase, Lmid_t ns)
  56 {
  57   struct r_debug_extended *r, **pp = NULL;
  58
  59   if (ns == LM_ID_BASE)
  60     {
  61       r = &_r_debug_extended;
  62       /* Initialize r_version to 1.  */
  63       if (_r_debug_extended.base.r_version == 0)
  64         _r_debug_extended.base.r_version = 1;
  65     }
  66   else if (DL_NNS > 1)
  67     {
  68       r = &GL(dl_ns)[ns]._ns_debug;
  69       if (r->base.r_brk == 0)
  70         {
  71           /* Add the new namespace to the linked list.  After a namespace
  72              is initialized, r_brk becomes non-zero.  A namespace becomes
  73              empty (r_map == NULL) when it is unused.  But it is never
  74              removed from the linked list.  */
  75           struct r_debug_extended *p;
  76           for (pp = &_r_debug_extended.r_next;
  77                (p = *pp) != NULL;
  78                pp = &p->r_next)
  79             ;
  80
  81           r->base.r_version = 2;
  82         }
  83     }
  84
  85   if (r->base.r_brk == 0)
  86     {
  87       /* Tell the debugger where to find the map of loaded objects.
  88          This function is called from dlopen.  Initialize the namespace
  89          only once.  */
  90       r->base.r_ldbase = ldbase ?: _r_debug_extended.base.r_ldbase;
  91       r->base.r_brk = (ElfW(Addr)) &_dl_debug_state;
  92       r->r_next = NULL;
  93     }
  94
  95   if (r->base.r_map == NULL)
  96     atomic_store_release (&r->base.r_map,
  97                           (void *) GL(dl_ns)[ns]._ns_loaded);
  98
  99   if (pp != NULL)
 100     {
 101       atomic_store_release (pp, r);
 102       /* Bump r_version to 2 for the new namespace.  */
 103       atomic_store_release (&_r_debug_extended.base.r_version, 2);
 104     }
 105
 106   return &r->base;
 107 }
 108
 109
 110 /* This function exists solely to have a breakpoint set on it by the
 111    debugger.  The debugger is supposed to find this function's address by
 112    examining the r_brk member of struct r_debug, but GDB 4.15 in fact looks
 113    for this particular symbol name in the PT_INTERP file.  */
 114 void
 115 _dl_debug_state (void)
 116 {
 117 }
 118 rtld_hidden_def (_dl_debug_state)