elf/link.h

   1 /* Data structure for communication from the run-time dynamic linker for
   2    loaded ELF shared objects.
   3    Copyright (C) 1995-2019 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 /* Rendezvous structure used by the run-time dynamic linker to communicate
  38    details of shared object loading to the debugger.  If the executable's
  39    dynamic section has a DT_DEBUG element, the run-time linker sets that
  40    element's value to the address where this structure can be found.  */
  41
  42 struct r_debug
  43   {
  44     int r_version;              /* Version number for this protocol.  */
  45
  46     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  47
  48     /* This is the address of a function internal to the run-time linker,
  49        that will always be called when the linker begins to map in a
  50        library or unmap it, and again when the mapping change is complete.
  51        The debugger can set a breakpoint at this address if it wants to
  52        notice shared object mapping changes.  */
  53     ElfW(Addr) r_brk;
  54     enum
  55       {
  56         /* This state value describes the mapping change taking place when
  57            the `r_brk' address is called.  */
  58         RT_CONSISTENT,          /* Mapping change is complete.  */
  59         RT_ADD,                 /* Beginning to add a new object.  */
  60         RT_DELETE               /* Beginning to remove an object mapping.  */
  61       } r_state;
  62
  63     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  64   };
  65
  66 /* This is the instance of that structure used by the dynamic linker.  */
  67 extern struct r_debug _r_debug;
  68
  69 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  70    of whatever module refers to `_DYNAMIC'.  So, to find its own
  71    `struct r_debug', a program could do:
  72      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
  73        if (dyn->d_tag == DT_DEBUG)
  74          r_debug = (struct r_debug *) dyn->d_un.d_ptr;
  75    */
  76 extern ElfW(Dyn) _DYNAMIC[];
  77
  78 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
  79    members form a chain of all the shared objects loaded at startup.
  80
  81    These data structures exist in space used by the run-time dynamic linker;
  82    modifying them may have disastrous results.  */
  83
  84 struct link_map
  85   {
  86     /* These first few members are part of the protocol with the debugger.
  87        This is the same format used in SVR4.  */
  88
  89     ElfW(Addr) l_addr;          /* Difference between the address in the ELF
  90                                    file and the addresses in memory.  */
  91     char *l_name;               /* Absolute file name object was found in.  */
  92     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
  93     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
  94   };
  95
  96 #ifdef __USE_GNU
  97
  98 /* Version numbers for la_version handshake interface.  */
  99 #define LAV_CURRENT     1
 100
 101 /* Activity types signaled through la_activity.  */
 102 enum
 103   {
 104     LA_ACT_CONSISTENT,          /* Link map consistent again.  */
 105     LA_ACT_ADD,                 /* New object will be added.  */
 106     LA_ACT_DELETE               /* Objects will be removed.  */
 107   };
 108
 109 /* Values representing origin of name for dynamic loading.  */
 110 enum
 111   {
 112     LA_SER_ORIG = 0x01,         /* Original name.  */
 113     LA_SER_LIBPATH = 0x02,      /* Directory from LD_LIBRARY_PATH.  */
 114     LA_SER_RUNPATH = 0x04,      /* Directory from RPATH/RUNPATH.  */
 115     LA_SER_CONFIG = 0x08,       /* Found through ldconfig.  */
 116     LA_SER_DEFAULT = 0x40,      /* Default directory.  */
 117     LA_SER_SECURE = 0x80        /* Unused.  */
 118   };
 119
 120 /* Values for la_objopen return value.  */
 121 enum
 122   {
 123     LA_FLG_BINDTO = 0x01,       /* Audit symbols bound to this object.  */
 124     LA_FLG_BINDFROM = 0x02      /* Audit symbols bound from this object.  */
 125   };
 126
 127 /* Values for la_symbind flags parameter.  */
 128 enum
 129   {
 130     LA_SYMB_NOPLTENTER = 0x01,  /* la_pltenter will not be called.  */
 131     LA_SYMB_NOPLTEXIT = 0x02,   /* la_pltexit will not be called.  */
 132     LA_SYMB_STRUCTCALL = 0x04,  /* Return value is a structure.  */
 133     LA_SYMB_DLSYM = 0x08,       /* Binding due to dlsym call.  */
 134     LA_SYMB_ALTVALUE = 0x10     /* Value has been changed by a previous
 135                                    la_symbind call.  */
 136   };
 137
 138 struct dl_phdr_info
 139   {
 140     ElfW(Addr) dlpi_addr;
 141     const char *dlpi_name;
 142     const ElfW(Phdr) *dlpi_phdr;
 143     ElfW(Half) dlpi_phnum;
 144
 145     /* Note: Following members were introduced after the first
 146        version of this structure was available.  Check the SIZE
 147        argument passed to the dl_iterate_phdr callback to determine
 148        whether or not each later member is available.  */
 149
 150     /* Incremented when a new object may have been added.  */
 151     __extension__ unsigned long long int dlpi_adds;
 152     /* Incremented when an object may have been removed.  */
 153     __extension__ unsigned long long int dlpi_subs;
 154
 155     /* If there is a PT_TLS segment, its module ID as used in
 156        TLS relocations, else zero.  */
 157     size_t dlpi_tls_modid;
 158
 159     /* The address of the calling thread's instance of this module's
 160        PT_TLS segment, if it has one and it has been allocated
 161        in the calling thread, otherwise a null pointer.  */
 162     void *dlpi_tls_data;
 163   };
 164
 165 __BEGIN_DECLS
 166
 167 extern int dl_iterate_phdr (int (*__callback) (struct dl_phdr_info *,
 168                                                size_t, void *),
 169                             void *__data);
 170
 171
 172 /* Prototypes for the ld.so auditing interfaces.  These are not
 173    defined anywhere in ld.so but instead have to be provided by the
 174    auditing DSO.  */
 175 extern unsigned int la_version (unsigned int __version);
 176 extern void la_activity (uintptr_t *__cookie, unsigned int __flag);
 177 extern char *la_objsearch (const char *__name, uintptr_t *__cookie,
 178                            unsigned int __flag);
 179 extern unsigned int la_objopen (struct link_map *__map, Lmid_t __lmid,
 180                                 uintptr_t *__cookie);
 181 extern void la_preinit (uintptr_t *__cookie);
 182 extern uintptr_t la_symbind32 (Elf32_Sym *__sym, unsigned int __ndx,
 183                                uintptr_t *__refcook, uintptr_t *__defcook,
 184                                unsigned int *__flags, const char *__symname);
 185 extern uintptr_t la_symbind64 (Elf64_Sym *__sym, unsigned int __ndx,
 186                                uintptr_t *__refcook, uintptr_t *__defcook,
 187                                unsigned int *__flags, const char *__symname);
 188 extern unsigned int la_objclose (uintptr_t *__cookie);
 189
 190 __END_DECLS
 191
 192 #endif
 193
 194 #endif /* link.h */