include/link.h

   1 /* Data structure for communication from the run-time dynamic linker for
   2    loaded ELF shared objects.
   3    Copyright (C) 1995-2002, 2003, 2004, 2005 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, write to the Free
  18    Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  19    02111-1307 USA.  */
  20
  21 #ifndef _LINK_H
  22 #define _LINK_H 1
  23
  24 #include <elf.h>
  25 #include <dlfcn.h>
  26 #include <stddef.h>
  27 #include <sys/types.h>
  28
  29 /* We use this macro to refer to ELF types independent of the native wordsize.
  30    `ElfW(TYPE)' is used in place of `Elf32_TYPE' or `Elf64_TYPE'.  */
  31 #define ElfW(type)      _ElfW (Elf, __ELF_NATIVE_CLASS, type)
  32 #define _ElfW(e,w,t)    _ElfW_1 (e, w, _##t)
  33 #define _ElfW_1(e,w,t)  e##w##t
  34
  35 #include <bits/elfclass.h>              /* Defines __ELF_NATIVE_CLASS.  */
  36 #include <bits/link.h>
  37 #include <bits/linkmap.h>
  38 #include <dl-lookupcfg.h>
  39 #include <tls.h>                /* Defines USE_TLS.  */
  40
  41 /* Rendezvous structure used by the run-time dynamic linker to communicate
  42    details of shared object loading to the debugger.  If the executable's
  43    dynamic section has a DT_DEBUG element, the run-time linker sets that
  44    element's value to the address where this structure can be found.  */
  45
  46 struct r_debug
  47   {
  48     int r_version;              /* Version number for this protocol.  */
  49
  50     struct link_map *r_map;     /* Head of the chain of loaded objects.  */
  51
  52     /* This is the address of a function internal to the run-time linker,
  53        that will always be called when the linker begins to map in a
  54        library or unmap it, and again when the mapping change is complete.
  55        The debugger can set a breakpoint at this address if it wants to
  56        notice shared object mapping changes.  */
  57     ElfW(Addr) r_brk;
  58     enum
  59       {
  60         /* This state value describes the mapping change taking place when
  61            the `r_brk' address is called.  */
  62         RT_CONSISTENT,          /* Mapping change is complete.  */
  63         RT_ADD,                 /* Beginning to add a new object.  */
  64         RT_DELETE               /* Beginning to remove an object mapping.  */
  65       } r_state;
  66
  67     ElfW(Addr) r_ldbase;        /* Base address the linker is loaded at.  */
  68   };
  69
  70 /* This is the instance of that structure used by the dynamic linker.  */
  71 extern struct r_debug _r_debug;
  72
  73 /* This symbol refers to the "dynamic structure" in the `.dynamic' section
  74    of whatever module refers to `_DYNAMIC'.  So, to find its own
  75    `struct r_debug', a program could do:
  76      for (dyn = _DYNAMIC; dyn->d_tag != DT_NULL; ++dyn)
  77        if (dyn->d_tag == DT_DEBUG)
  78          r_debug = (struct r_debug *) dyn->d_un.d_ptr;
  79    */
  80 extern ElfW(Dyn) _DYNAMIC[];
  81
  82
  83 /* Some internal data structures of the dynamic linker used in the
  84    linker map.  We only provide forward declarations.  */
  85 struct libname_list;
  86 struct r_found_version;
  87 struct r_search_path_elem;
  88
  89 /* Forward declaration.  */
  90 struct link_map;
  91
  92 /* Structure to describe a single list of scope elements.  The lookup
  93    functions get passed an array of pointers to such structures.  */
  94 struct r_scope_elem
  95 {
  96   /* Array of maps for the scope.  */
  97   struct link_map **r_list;
  98   /* Number of entries in the scope.  */
  99   unsigned int r_nlist;
 100 };
 101
 102
 103 /* Structure to record search path and allocation mechanism.  */
 104 struct r_search_path_struct
 105   {
 106     struct r_search_path_elem **dirs;
 107     int malloced;
 108   };
 109
 110
 111 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
 112    members form a chain of all the shared objects loaded at startup.
 113
 114    These data structures exist in space used by the run-time dynamic linker;
 115    modifying them may have disastrous results.
 116
 117    This data structure might change in future, if necessary.  User-level
 118    programs must avoid defining objects of this type.  */
 119
 120 struct link_map
 121   {
 122     /* These first few members are part of the protocol with the debugger.
 123        This is the same format used in SVR4.  */
 124
 125     ElfW(Addr) l_addr;          /* Base address shared object is loaded at.  */
 126     char *l_name;               /* Absolute file name object was found in.  */
 127     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 128     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 129
 130     /* All following members are internal to the dynamic linker.
 131        They may change without notice.  */
 132
 133     /* This is an element which is only ever different from a pointer to
 134        the very same copy of this type for ld.so when it is used in more
 135        than one namespace.  */
 136     struct link_map *l_real;
 137
 138     /* Number of the namespace this link map belongs to.  */
 139     Lmid_t l_ns;
 140
 141     struct libname_list *l_libname;
 142     /* Indexed pointers to dynamic section.
 143        [0,DT_NUM) are indexed by the processor-independent tags.
 144        [DT_NUM,DT_NUM+DT_THISPROCNUM) are indexed by the tag minus DT_LOPROC.
 145        [DT_NUM+DT_THISPROCNUM,DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM) are
 146        indexed by DT_VERSIONTAGIDX(tagvalue).
 147        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
 148         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM) are indexed by
 149        DT_EXTRATAGIDX(tagvalue).
 150        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM,
 151         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM) are
 152        indexed by DT_VALTAGIDX(tagvalue) and
 153        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM,
 154         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM+DT_ADDRNUM)
 155        are indexed by DT_ADDRTAGIDX(tagvalue), see <elf.h>.  */
 156
 157     ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
 158                      + DT_EXTRANUM + DT_VALNUM + DT_ADDRNUM];
 159     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 160     ElfW(Addr) l_entry;         /* Entry point location.  */
 161     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 162     ElfW(Half) l_ldnum; /* Number of dynamic segment entries.  */
 163
 164     /* Array of DT_NEEDED dependencies and their dependencies, in
 165        dependency order for symbol lookup (with and without
 166        duplicates).  There is no entry before the dependencies have
 167        been loaded.  */
 168     struct r_scope_elem l_searchlist;
 169
 170     /* We need a special searchlist to process objects marked with
 171        DT_SYMBOLIC.  */
 172     struct r_scope_elem l_symbolic_searchlist;
 173
 174     /* Dependent object that first caused this object to be loaded.  */
 175     struct link_map *l_loader;
 176
 177     /* Symbol hash table.  */
 178     Elf_Symndx l_nbuckets;
 179     const Elf_Symndx *l_buckets, *l_chain;
 180
 181     unsigned int l_direct_opencount; /* Reference count for dlopen/dlclose.  */
 182     enum                        /* Where this object came from.  */
 183       {
 184         lt_executable,          /* The main executable program.  */
 185         lt_library,             /* Library needed by main executable.  */
 186         lt_loaded               /* Extra run-time loaded shared object.  */
 187       } l_type:2;
 188     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 189     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 190     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 191     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 192     unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
 193                                         to by `l_phdr' is allocated.  */
 194     unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in
 195                                       the l_libname list.  */
 196     unsigned int l_faked:1;     /* Nonzero if this is a faked descriptor
 197                                    without associated file.  */
 198     unsigned int l_need_tls_init:1; /* Nonzero if GL(dl_init_static_tls)
 199                                        should be called on this link map
 200                                        when relocation finishes.  */
 201     unsigned int l_used:1;      /* Nonzero if the DSO is used.  */
 202     unsigned int l_auditing:1;  /* Nonzero if the DSO is used in auditing.  */
 203     unsigned int l_audit_any_plt:1; /* Nonzero if at least one audit module
 204                                        is interested in the PLT interception.*/
 205     unsigned int l_removed:1;   /* Nozero if the object cannot be used anymore
 206                                    since it is removed.  */
 207
 208     /* Array with version names.  */
 209     unsigned int l_nversions;
 210     struct r_found_version *l_versions;
 211
 212     /* Collected information about own RPATH directories.  */
 213     struct r_search_path_struct l_rpath_dirs;
 214
 215     /* Collected results of relocation while profiling.  */
 216     struct reloc_result
 217     {
 218       DL_FIXUP_VALUE_TYPE addr;
 219       struct link_map *bound;
 220       unsigned int boundndx;
 221       uint32_t enterexit;
 222       unsigned int flags;
 223     } *l_reloc_result;
 224
 225     /* Pointer to the version information if available.  */
 226     ElfW(Versym) *l_versyms;
 227
 228     /* String specifying the path where this object was found.  */
 229     const char *l_origin;
 230
 231     /* Start and finish of memory map for this object.  l_map_start
 232        need not be the same as l_addr.  */
 233     ElfW(Addr) l_map_start, l_map_end;
 234     /* End of the executable part of the mapping.  */
 235     ElfW(Addr) l_text_end;
 236
 237     /* Default array for 'l_scope'.  */
 238     struct r_scope_elem *l_scope_mem[4];
 239     /* Size of array allocated for 'l_scope'.  */
 240     size_t l_scope_max;
 241     /* This is an array defining the lookup scope for this link map.
 242        There are at most three different scope lists.  */
 243     struct r_scope_elem **l_scope;
 244
 245     /* A similar array, this time only with the local scope.  This is
 246        used occasionally.  */
 247     struct r_scope_elem *l_local_scope[2];
 248
 249     /* This information is kept to check for sure whether a shared
 250        object is the same as one already loaded.  */
 251     dev_t l_dev;
 252     ino64_t l_ino;
 253
 254     /* Collected information about own RUNPATH directories.  */
 255     struct r_search_path_struct l_runpath_dirs;
 256
 257     /* List of object in order of the init and fini calls.  */
 258     struct link_map **l_initfini;
 259
 260     /* List of the dependencies introduced through symbol binding.  */
 261     unsigned int l_reldepsmax;
 262     unsigned int l_reldepsact;
 263     struct link_map **l_reldeps;
 264
 265     /* Various flag words.  */
 266     ElfW(Word) l_feature_1;
 267     ElfW(Word) l_flags_1;
 268     ElfW(Word) l_flags;
 269
 270     /* Temporarily used in `dl_close'.  */
 271     int l_idx;
 272
 273     struct link_map_machine l_mach;
 274
 275     struct
 276     {
 277       const ElfW(Sym) *sym;
 278       int type_class;
 279       struct link_map *value;
 280       const ElfW(Sym) *ret;
 281     } l_lookup_cache;
 282
 283 #ifdef USE_TLS
 284     /* Thread-local storage related info.  */
 285
 286     /* Start of the initialization image.  */
 287     void *l_tls_initimage;
 288     /* Size of the initialization image.  */
 289     size_t l_tls_initimage_size;
 290     /* Size of the TLS block.  */
 291     size_t l_tls_blocksize;
 292     /* Alignment requirement of the TLS block.  */
 293     size_t l_tls_align;
 294     /* Offset of first byte module alignment.  */
 295     size_t l_tls_firstbyte_offset;
 296 # ifndef NO_TLS_OFFSET
 297 #  define NO_TLS_OFFSET 0
 298 # endif
 299     /* For objects present at startup time: offset in the static TLS block.  */
 300     ptrdiff_t l_tls_offset;
 301     /* Index of the module in the dtv array.  */
 302     size_t l_tls_modid;
 303 #endif
 304
 305     /* Information used to change permission after the relocations are
 306        done.  */
 307     ElfW(Addr) l_relro_addr;
 308     size_t l_relro_size;
 309
 310     /* Audit information.  This array apparent must be the last in the
 311        structure.  Never add something after it.  */
 312     struct auditstate
 313     {
 314       uintptr_t cookie;
 315       unsigned int bindflags;
 316     } l_audit[0];
 317   };
 318
 319 /* Version numbers for la_version handshake interface.  */
 320 #define LAV_CURRENT     1
 321
 322 /* Activity types signaled through la_activity.  */
 323 enum
 324   {
 325     LA_ACT_CONSISTENT,
 326     LA_ACT_ADD,
 327     LA_ACT_DELETE
 328   };
 329
 330 /* Values representing origin of name for dynamic loading.  */
 331 enum
 332   {
 333     LA_SER_ORIG = 0x01,         /* Original name.  */
 334     LA_SER_LIBPATH = 0x02,      /* Directory from LD_LIBRARY_PATH.  */
 335     LA_SER_RUNPATH = 0x04,      /* Directory from RPATH/RUNPATH.  */
 336     LA_SER_CONFIG = 0x08,       /* Found through ldconfig.  */
 337     LA_SER_DEFAULT = 0x40,      /* Default directory.  */
 338     LA_SER_SECURE = 0x80        /* Unused.  */
 339   };
 340
 341 /* Values for la_objopen return value.  */
 342 enum
 343   {
 344     LA_FLG_BINDTO = 0x01,       /* Audit symbols bound to this object.  */
 345     LA_FLG_BINDFROM = 0x02      /* Audit symbols bound from this object.  */
 346   };
 347
 348 /* Values for la_symbind flags parameter.  */
 349 enum
 350   {
 351     LA_SYMB_NOPLTENTER = 0x01,  /* la_pltenter will not be called.  */
 352     LA_SYMB_NOPLTEXIT = 0x02,   /* la_pltexit will not be called.  */
 353     LA_SYMB_STRUCTCALL = 0x04,  /* Return value is a structure.  */
 354     LA_SYMB_DLSYM = 0x08,       /* Binding due to dlsym call.  */
 355     LA_SYMB_ALTVALUE = 0x10     /* Value has been changed by a previous
 356                                    la_symbind call.  */
 357   };
 358
 359 #if __ELF_NATIVE_CLASS == 32
 360 # define symbind symbind32
 361 #elif __ELF_NATIVE_CLASS == 64
 362 # define symbind symbind64
 363 #else
 364 # error "__ELF_NATIVE_CLASS must be defined"
 365 #endif
 366
 367 struct dl_phdr_info
 368   {
 369     ElfW(Addr) dlpi_addr;
 370     const char *dlpi_name;
 371     const ElfW(Phdr) *dlpi_phdr;
 372     ElfW(Half) dlpi_phnum;
 373
 374     unsigned long long int dlpi_adds;
 375     unsigned long long int dlpi_subs;
 376   };
 377
 378 extern int dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 379                                              size_t size, void *data),
 380                             void *data);
 381 extern int __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 382                                                size_t size, void *data),
 383                               void *data);
 384
 385 #endif /* link.h */