elf/link.h

   1 /* Data structure for communication from the run-time dynamic linker for
   2    loaded ELF shared objects.
   3    Copyright (C) 1995-2022 Free Software Foundation, Inc.
   4    This file is part of the GNU C Library.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <https://www.gnu.org/licenses/>.  */
  19
  20 #ifndef _LINK_H
  21 #define _LINK_H 1
  22
  23 #include <features.h>
  24 #include <elf.h>
  25 #include <dlfcn.h>
  26 #include <sys/types.h>
  27
  28 /* We use this macro to refer to ELF types independent of the native wordsize.
  29    `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
  30 #define ElfW(type)      _ElfW (Elf, __ELF_NATIVE_CLASS, type)
  31 #define _ElfW(e,w,t)    _ElfW_1 (e, w, _##t)
  32 #define _ElfW_1(e,w,t)  e##w##t
  33
  34 #include <bits/elfclass.h>              /* Defines __ELF_NATIVE_CLASS.  */
  35 #include <bits/link.h>
  36
  37 /* The legacy rendezvous structure used by the run-time dynamic linker to
  38    communicate details of shared object loading to the debugger.  */
  39
  40 struct r_debug
  41   {
  42     /* Version number for this protocol.  It should be greater than 0.  */
  43     int r_version;
  44
  45     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  46
  47     /* This is the address of a function internal to the run-time linker,
  48        that will always be called when the linker begins to map in a
  49        library or unmap it, and again when the mapping change is complete.
  50        The debugger can set a breakpoint at this address if it wants to
  51        notice shared object mapping changes.  */
  52     ElfW(Addr) r_brk;
  53     enum
  54       {
  55         /* This state value describes the mapping change taking place when
  56            the `r_brk' address is called.  */
  57         RT_CONSISTENT,          /* Mapping change is complete.  */
  58         RT_ADD,                 /* Beginning to add a new object.  */
  59         RT_DELETE               /* Beginning to remove an object mapping.  */
  60       } r_state;
  61
  62     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  63   };
  64
  65 /* This is the symbol of that structure provided by the dynamic linker.  */
  66 extern struct r_debug _r_debug;
  67
  68 /* The extended rendezvous structure used by the run-time dynamic linker
  69    to communicate details of shared object loading to the debugger.  If
  70    the executable's dynamic section has a DT_DEBUG element, the run-time
  71    linker sets that element's value to the address where this structure
  72    can be found.  */
  73
  74 struct r_debug_extended
  75   {
  76     struct r_debug base;
  77
  78     /* The following field is added by r_version == 2.  */
  79
  80     /* Link to the next r_debug_extended structure.  Each r_debug_extended
  81        structure represents a different namespace.  The first
  82        r_debug_extended structure is for the default namespace.  */
  83     struct r_debug_extended *r_next;
  84   };
  85
  86 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  87    of whatever module refers to `_DYNAMIC'.  So, to find its own
  88    `struct r_debug_extended', a program could do:
  89      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
  90        if (dyn->d_tag == DT_DEBUG)
  91          r_debug_extended = (struct r_debug_extended *) dyn->d_un.d_ptr;
  92  */
  93 extern ElfW(Dyn) _DYNAMIC[];
  94
  95 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
  96    members form a chain of all the shared objects loaded at startup.
  97
  98    These data structures exist in space used by the run-time dynamic linker;
  99    modifying them may have disastrous results.  */
 100
 101 struct link_map
 102   {
 103     /* These first few members are part of the protocol with the debugger.
 104        This is the same format used in SVR4.  */
 105
 106     ElfW(Addr) l_addr;          /* Difference between the address in the ELF
 107                                    file and the addresses in memory.  */
 108     char *l_name;               /* Absolute file name object was found in.  */
 109     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 110     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 111   };
 112
 113 #ifdef __USE_GNU
 114
 115 /* Version numbers for la_version handshake interface.  */
 116 #include <bits/link_lavcurrent.h>
 117
 118 /* Activity types signaled through la_activity.  */
 119 enum
 120   {
 121     LA_ACT_CONSISTENT,          /* Link map consistent again.  */
 122     LA_ACT_ADD,                 /* New object will be added.  */
 123     LA_ACT_DELETE               /* Objects will be removed.  */
 124   };
 125
 126 /* Values representing origin of name for dynamic loading.  */
 127 enum
 128   {
 129     LA_SER_ORIG = 0x01,         /* Original name.  */
 130     LA_SER_LIBPATH = 0x02,      /* Directory from LD_LIBRARY_PATH.  */
 131     LA_SER_RUNPATH = 0x04,      /* Directory from RPATH/RUNPATH.  */
 132     LA_SER_CONFIG = 0x08,       /* Found through ldconfig.  */
 133     LA_SER_DEFAULT = 0x40,      /* Default directory.  */
 134     LA_SER_SECURE = 0x80        /* Unused.  */
 135   };
 136
 137 /* Values for la_objopen return value.  */
 138 enum
 139   {
 140     LA_FLG_BINDTO = 0x01,       /* Audit symbols bound to this object.  */
 141     LA_FLG_BINDFROM = 0x02      /* Audit symbols bound from this object.  */
 142   };
 143
 144 /* Values for la_symbind flags parameter.  */
 145 enum
 146   {
 147     LA_SYMB_NOPLTENTER = 0x01,  /* la_pltenter will not be called.  */
 148     LA_SYMB_NOPLTEXIT = 0x02,   /* la_pltexit will not be called.  */
 149     LA_SYMB_STRUCTCALL = 0x04,  /* Return value is a structure.  */
 150     LA_SYMB_DLSYM = 0x08,       /* Binding due to dlsym call.  */
 151     LA_SYMB_ALTVALUE = 0x10     /* Value has been changed by a previous
 152                                    la_symbind call.  */
 153   };
 154
 155 struct dl_phdr_info
 156   {
 157     ElfW(Addr) dlpi_addr;
 158     const char *dlpi_name;
 159     const ElfW(Phdr) *dlpi_phdr;
 160     ElfW(Half) dlpi_phnum;
 161
 162     /* Note: Following members were introduced after the first
 163        version of this structure was available.  Check the SIZE
 164        argument passed to the dl_iterate_phdr callback to determine
 165        whether or not each later member is available.  */
 166
 167     /* Incremented when a new object may have been added.  */
 168     __extension__ unsigned long long int dlpi_adds;
 169     /* Incremented when an object may have been removed.  */
 170     __extension__ unsigned long long int dlpi_subs;
 171
 172     /* If there is a PT_TLS segment, its module ID as used in
 173        TLS relocations, else zero.  */
 174     size_t dlpi_tls_modid;
 175
 176     /* The address of the calling thread's instance of this module's
 177        PT_TLS segment, if it has one and it has been allocated
 178        in the calling thread, otherwise a null pointer.  */
 179     void *dlpi_tls_data;
 180   };
 181
 182 __BEGIN_DECLS
 183
 184 extern int dl_iterate_phdr (int (*__callback) (struct dl_phdr_info *,
 185                                                size_t, void *),
 186                             void *__data);
 187
 188
 189 /* Prototypes for the ld.so auditing interfaces.  These are not
 190    defined anywhere in ld.so but instead have to be provided by the
 191    auditing DSO.  */
 192 extern unsigned int la_version (unsigned int __version);
 193 extern void la_activity (uintptr_t *__cookie, unsigned int __flag);
 194 extern char *la_objsearch (const char *__name, uintptr_t *__cookie,
 195                            unsigned int __flag);
 196 extern unsigned int la_objopen (struct link_map *__map, Lmid_t __lmid,
 197                                 uintptr_t *__cookie);
 198 extern void la_preinit (uintptr_t *__cookie);
 199 extern uintptr_t la_symbind32 (Elf32_Sym *__sym, unsigned int __ndx,
 200                                uintptr_t *__refcook, uintptr_t *__defcook,
 201                                unsigned int *__flags, const char *__symname);
 202 extern uintptr_t la_symbind64 (Elf64_Sym *__sym, unsigned int __ndx,
 203                                uintptr_t *__refcook, uintptr_t *__defcook,
 204                                unsigned int *__flags, const char *__symname);
 205 extern unsigned int la_objclose (uintptr_t *__cookie);
 206
 207 __END_DECLS
 208
 209 #endif
 210
 211 #endif /* link.h */