include/link.h

   1 /* Data structure for communication from the run-time dynamic linker for
   2    loaded ELF shared objects.
   3    Copyright (C) 1995-2021 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 _PRIVATE_LINK_H
  21 #define _PRIVATE_LINK_H 1
  22
  23 #ifdef _LINK_H
  24 # error this should be impossible
  25 #endif
  26
  27 # ifndef _ISOMAC
  28 /* Get most of the contents from the public header, but we define a
  29    different `struct link_map' type for private use.  The la_objopen
  30    prototype uses the type, so we have to declare it separately.  */
  31 #  define link_map      link_map_public
  32 #  define la_objopen    la_objopen_wrongproto
  33 # endif
  34
  35 #include <elf/link.h>
  36
  37 # ifndef _ISOMAC
  38
  39 #undef  link_map
  40 #undef  la_objopen
  41
  42 struct link_map;
  43 extern unsigned int la_objopen (struct link_map *__map, Lmid_t __lmid,
  44                                 uintptr_t *__cookie);
  45
  46 #include <stdint.h>
  47 #include <stddef.h>
  48 #include <linkmap.h>
  49 #include <dl-fileid.h>
  50 #include <dl-lookupcfg.h>
  51 #include <tls.h>
  52 #include <libc-lock.h>
  53
  54
  55 /* Some internal data structures of the dynamic linker used in the
  56    linker map.  We only provide forward declarations.  */
  57 struct libname_list;
  58 struct r_found_version;
  59 struct r_search_path_elem;
  60
  61 /* Forward declaration.  */
  62 struct link_map;
  63
  64 /* Structure to describe a single list of scope elements.  The lookup
  65    functions get passed an array of pointers to such structures.  */
  66 struct r_scope_elem
  67 {
  68   /* Array of maps for the scope.  */
  69   struct link_map **r_list;
  70   /* Number of entries in the scope.  */
  71   unsigned int r_nlist;
  72 };
  73
  74
  75 /* Structure to record search path and allocation mechanism.  */
  76 struct r_search_path_struct
  77   {
  78     struct r_search_path_elem **dirs;
  79     int malloced;
  80   };
  81
  82 /* Search path information computed by _dl_init_paths.  */
  83 extern struct r_search_path_struct __rtld_search_dirs attribute_hidden;
  84 extern struct r_search_path_struct __rtld_env_path_list attribute_hidden;
  85
  86 /* Structure describing a loaded shared object.  The `l_next' and `l_prev'
  87    members form a chain of all the shared objects loaded at startup.
  88
  89    These data structures exist in space used by the run-time dynamic linker;
  90    modifying them may have disastrous results.
  91
  92    This data structure might change in future, if necessary.  User-level
  93    programs must avoid defining objects of this type.  */
  94
  95 struct link_map
  96   {
  97     /* These first few members are part of the protocol with the debugger.
  98        This is the same format used in SVR4.  */
  99
 100     ElfW(Addr) l_addr;          /* Difference between the address in the ELF
 101                                    file and the addresses in memory.  */
 102     char *l_name;               /* Absolute file name object was found in.  */
 103     ElfW(Dyn) *l_ld;            /* Dynamic section of the shared object.  */
 104     struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */
 105
 106     /* All following members are internal to the dynamic linker.
 107        They may change without notice.  */
 108
 109     /* This is an element which is only ever different from a pointer to
 110        the very same copy of this type for ld.so when it is used in more
 111        than one namespace.  */
 112     struct link_map *l_real;
 113
 114     /* Number of the namespace this link map belongs to.  */
 115     Lmid_t l_ns;
 116
 117     struct libname_list *l_libname;
 118     /* Indexed pointers to dynamic section.
 119        [0,DT_NUM) are indexed by the processor-independent tags.
 120        [DT_NUM,DT_NUM+DT_THISPROCNUM) are indexed by the tag minus DT_LOPROC.
 121        [DT_NUM+DT_THISPROCNUM,DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM) are
 122        indexed by DT_VERSIONTAGIDX(tagvalue).
 123        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
 124         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM) are indexed by
 125        DT_EXTRATAGIDX(tagvalue).
 126        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM,
 127         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM) are
 128        indexed by DT_VALTAGIDX(tagvalue) and
 129        [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM,
 130         DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM+DT_ADDRNUM)
 131        are indexed by DT_ADDRTAGIDX(tagvalue), see <elf.h>.  */
 132
 133     ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
 134                       + DT_EXTRANUM + DT_VALNUM + DT_ADDRNUM];
 135     const ElfW(Phdr) *l_phdr;   /* Pointer to program header table in core.  */
 136     ElfW(Addr) l_entry;         /* Entry point location.  */
 137     ElfW(Half) l_phnum;         /* Number of program header entries.  */
 138     ElfW(Half) l_ldnum;         /* Number of dynamic segment entries.  */
 139
 140     /* Array of DT_NEEDED dependencies and their dependencies, in
 141        dependency order for symbol lookup (with and without
 142        duplicates).  There is no entry before the dependencies have
 143        been loaded.  */
 144     struct r_scope_elem l_searchlist;
 145
 146     /* We need a special searchlist to process objects marked with
 147        DT_SYMBOLIC.  */
 148     struct r_scope_elem l_symbolic_searchlist;
 149
 150     /* Dependent object that first caused this object to be loaded.  */
 151     struct link_map *l_loader;
 152
 153     /* Array with version names.  */
 154     struct r_found_version *l_versions;
 155     unsigned int l_nversions;
 156
 157     /* Symbol hash table.  */
 158     Elf_Symndx l_nbuckets;
 159     Elf32_Word l_gnu_bitmask_idxbits;
 160     Elf32_Word l_gnu_shift;
 161     const ElfW(Addr) *l_gnu_bitmask;
 162     union
 163     {
 164       const Elf32_Word *l_gnu_buckets;
 165       const Elf_Symndx *l_chain;
 166     };
 167     union
 168     {
 169       const Elf32_Word *l_gnu_chain_zero;
 170       const Elf_Symndx *l_buckets;
 171     };
 172
 173     unsigned int l_direct_opencount; /* Reference count for dlopen/dlclose.  */
 174     enum                        /* Where this object came from.  */
 175       {
 176         lt_executable,          /* The main executable program.  */
 177         lt_library,             /* Library needed by main executable.  */
 178         lt_loaded               /* Extra run-time loaded shared object.  */
 179       } l_type:2;
 180     unsigned int l_relocated:1; /* Nonzero if object's relocations done.  */
 181     unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
 182     unsigned int l_global:1;    /* Nonzero if object in _dl_global_scope.  */
 183     unsigned int l_reserved:2;  /* Reserved for internal use.  */
 184     unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
 185                                         to by `l_phdr' is allocated.  */
 186     unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in
 187                                       the l_libname list.  */
 188     unsigned int l_faked:1;     /* Nonzero if this is a faked descriptor
 189                                    without associated file.  */
 190     unsigned int l_need_tls_init:1; /* Nonzero if GL(dl_init_static_tls)
 191                                        should be called on this link map
 192                                        when relocation finishes.  */
 193     unsigned int l_auditing:1;  /* Nonzero if the DSO is used in auditing.  */
 194     unsigned int l_audit_any_plt:1; /* Nonzero if at least one audit module
 195                                        is interested in the PLT interception.*/
 196     unsigned int l_removed:1;   /* Nozero if the object cannot be used anymore
 197                                    since it is removed.  */
 198     unsigned int l_contiguous:1; /* Nonzero if inter-segment holes are
 199                                     mprotected or if no holes are present at
 200                                     all.  */
 201     unsigned int l_symbolic_in_local_scope:1; /* Nonzero if l_local_scope
 202                                                  during LD_TRACE_PRELINKING=1
 203                                                  contains any DT_SYMBOLIC
 204                                                  libraries.  */
 205     unsigned int l_free_initfini:1; /* Nonzero if l_initfini can be
 206                                        freed, ie. not allocated with
 207                                        the dummy malloc in ld.so.  */
 208
 209     /* NODELETE status of the map.  Only valid for maps of type
 210        lt_loaded.  Lazy binding sets l_nodelete_active directly,
 211        potentially from signal handlers.  Initial loading of an
 212        DF_1_NODELETE object set l_nodelete_pending.  Relocation may
 213        set l_nodelete_pending as well.  l_nodelete_pending maps are
 214        promoted to l_nodelete_active status in the final stages of
 215        dlopen, prior to calling ELF constructors.  dlclose only
 216        refuses to unload l_nodelete_active maps, the pending status is
 217        ignored.  */
 218     bool l_nodelete_active;
 219     bool l_nodelete_pending;
 220
 221 #include <link_map.h>
 222
 223     /* Collected information about own RPATH directories.  */
 224     struct r_search_path_struct l_rpath_dirs;
 225
 226     /* Collected results of relocation while profiling.  */
 227     struct reloc_result
 228     {
 229       DL_FIXUP_VALUE_TYPE addr;
 230       struct link_map *bound;
 231       unsigned int boundndx;
 232       uint32_t enterexit;
 233       unsigned int flags;
 234       /* CONCURRENCY NOTE: This is used to guard the concurrent initialization
 235          of the relocation result across multiple threads.  See the more
 236          detailed notes in elf/dl-runtime.c.  */
 237       unsigned int init;
 238     } *l_reloc_result;
 239
 240     /* Pointer to the version information if available.  */
 241     ElfW(Versym) *l_versyms;
 242
 243     /* String specifying the path where this object was found.  */
 244     const char *l_origin;
 245
 246     /* Start and finish of memory map for this object.  l_map_start
 247        need not be the same as l_addr.  */
 248     ElfW(Addr) l_map_start, l_map_end;
 249     /* End of the executable part of the mapping.  */
 250     ElfW(Addr) l_text_end;
 251
 252     /* Default array for 'l_scope'.  */
 253     struct r_scope_elem *l_scope_mem[4];
 254     /* Size of array allocated for 'l_scope'.  */
 255     size_t l_scope_max;
 256     /* This is an array defining the lookup scope for this link map.
 257        There are initially at most three different scope lists.  */
 258     struct r_scope_elem **l_scope;
 259
 260     /* A similar array, this time only with the local scope.  This is
 261        used occasionally.  */
 262     struct r_scope_elem *l_local_scope[2];
 263
 264     /* This information is kept to check for sure whether a shared
 265        object is the same as one already loaded.  */
 266     struct r_file_id l_file_id;
 267
 268     /* Collected information about own RUNPATH directories.  */
 269     struct r_search_path_struct l_runpath_dirs;
 270
 271     /* List of object in order of the init and fini calls.  */
 272     struct link_map **l_initfini;
 273
 274     /* List of the dependencies introduced through symbol binding.  */
 275     struct link_map_reldeps
 276       {
 277         unsigned int act;
 278         struct link_map *list[];
 279       } *l_reldeps;
 280     unsigned int l_reldepsmax;
 281
 282     /* Nonzero if the DSO is used.  */
 283     unsigned int l_used;
 284
 285     /* Various flag words.  */
 286     ElfW(Word) l_feature_1;
 287     ElfW(Word) l_flags_1;
 288     ElfW(Word) l_flags;
 289
 290     /* Temporarily used in `dl_close'.  */
 291     int l_idx;
 292
 293     struct link_map_machine l_mach;
 294
 295     struct
 296     {
 297       const ElfW(Sym) *sym;
 298       int type_class;
 299       struct link_map *value;
 300       const ElfW(Sym) *ret;
 301     } l_lookup_cache;
 302
 303     /* Thread-local storage related info.  */
 304
 305     /* Start of the initialization image.  */
 306     void *l_tls_initimage;
 307     /* Size of the initialization image.  */
 308     size_t l_tls_initimage_size;
 309     /* Size of the TLS block.  */
 310     size_t l_tls_blocksize;
 311     /* Alignment requirement of the TLS block.  */
 312     size_t l_tls_align;
 313     /* Offset of first byte module alignment.  */
 314     size_t l_tls_firstbyte_offset;
 315 #ifndef NO_TLS_OFFSET
 316 # define NO_TLS_OFFSET  0
 317 #endif
 318 #ifndef FORCED_DYNAMIC_TLS_OFFSET
 319 # if NO_TLS_OFFSET == 0
 320 #  define FORCED_DYNAMIC_TLS_OFFSET -1
 321 # elif NO_TLS_OFFSET == -1
 322 #  define FORCED_DYNAMIC_TLS_OFFSET -2
 323 # else
 324 #  error "FORCED_DYNAMIC_TLS_OFFSET is not defined"
 325 # endif
 326 #endif
 327     /* For objects present at startup time: offset in the static TLS block.  */
 328     ptrdiff_t l_tls_offset;
 329     /* Index of the module in the dtv array.  */
 330     size_t l_tls_modid;
 331
 332     /* Number of thread_local objects constructed by this DSO.  This is
 333        atomically accessed and modified and is not always protected by the load
 334        lock.  See also: CONCURRENCY NOTES in cxa_thread_atexit_impl.c.  */
 335     size_t l_tls_dtor_count;
 336
 337     /* Information used to change permission after the relocations are
 338        done.  */
 339     ElfW(Addr) l_relro_addr;
 340     size_t l_relro_size;
 341
 342     unsigned long long int l_serial;
 343   };
 344
 345 /* Information used by audit modules.  For most link maps, this data
 346    immediate follows the link map in memory.  For the dynamic linker,
 347    it is allocated separately.  See link_map_audit_state in
 348    <ldsodefs.h>.  */
 349 struct auditstate
 350 {
 351   uintptr_t cookie;
 352   unsigned int bindflags;
 353 };
 354
 355
 356 #if __ELF_NATIVE_CLASS == 32
 357 # define symbind symbind32
 358 #elif __ELF_NATIVE_CLASS == 64
 359 # define symbind symbind64
 360 #else
 361 # error "__ELF_NATIVE_CLASS must be defined"
 362 #endif
 363
 364 extern int __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
 365                                                size_t size, void *data),
 366                               void *data);
 367 hidden_proto (__dl_iterate_phdr)
 368
 369 /* We use this macro to refer to ELF macros independent of the native
 370    wordsize.  `ELFW(R_TYPE)' is used in place of `ELF32_R_TYPE' or
 371    `ELF64_R_TYPE'.  */
 372 #define ELFW(type)      _ElfW (ELF, __ELF_NATIVE_CLASS, type)
 373
 374 # endif /* !_ISOMAC */
 375 #endif /* include/link.h */