glibc/include/link.h

/* Data structure for communication from the run-time dynamic linker for
   loaded ELF shared objects.
   Copyright (C) 1995-2024 Free Software Foundation, Inc.
   This file is part of the GNU C Library.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Lesser General Public
   License as published by the Free Software Foundation; either
   version 2.1 of the License, or (at your option) any later version.

   The GNU C Library is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
   Lesser General Public License for more details.

   You should have received a copy of the GNU Lesser General Public
   License along with the GNU C Library; if not, see
   <https://www.gnu.org/licenses/>.  */

#ifndef	_PRIVATE_LINK_H
#define	_PRIVATE_LINK_H	1

#ifdef _LINK_H
# error this should be impossible
#endif

# ifndef _ISOMAC
/* Get most of the contents from the public header, but we define a
   different `struct link_map' type for private use.  The la_objopen
   prototype uses the type, so we have to declare it separately.  */
#  define link_map	link_map_public
#  define la_objopen	la_objopen_wrongproto
# endif

#include <elf/link.h>

# ifndef _ISOMAC

#undef	link_map
#undef	la_objopen

struct link_map;
extern unsigned int la_objopen (struct link_map *__map, Lmid_t __lmid,
				uintptr_t *__cookie);

#include <stdint.h>
#include <stddef.h>
#include <linkmap.h>
#include <dl-fileid.h>
#include <dl-lookupcfg.h>
#include <tls.h>
#include <libc-lock.h>


/* Some internal data structures of the dynamic linker used in the
   linker map.  We only provide forward declarations.  */
struct libname_list;
struct r_found_version;
struct r_search_path_elem;

/* Forward declaration.  */
struct link_map;

/* Structure to describe a single list of scope elements.  The lookup
   functions get passed an array of pointers to such structures.  */
struct r_scope_elem
{
  /* Array of maps for the scope.  */
  struct link_map **r_list;
  /* Number of entries in the scope.  */
  unsigned int r_nlist;
};


/* Structure to record search path and allocation mechanism.  */
struct r_search_path_struct
  {
    struct r_search_path_elem **dirs;
    int malloced;
  };

/* Search path information computed by _dl_init_paths.  */
extern struct r_search_path_struct __rtld_search_dirs attribute_hidden;
extern struct r_search_path_struct __rtld_env_path_list attribute_hidden;

/* Structure describing a loaded shared object.  The `l_next' and `l_prev'
   members form a chain of all the shared objects loaded at startup.

   These data structures exist in space used by the run-time dynamic linker;
   modifying them may have disastrous results.

   This data structure might change in future, if necessary.  User-level
   programs must avoid defining objects of this type.  */

struct link_map
  {
    /* These first few members are part of the protocol with the debugger.
       This is the same format used in SVR4.  */

    ElfW(Addr) l_addr;		/* Difference between the address in the ELF
				   file and the addresses in memory.  */
    char *l_name;		/* Absolute file name object was found in.  */
    ElfW(Dyn) *l_ld;		/* Dynamic section of the shared object.  */
    struct link_map *l_next, *l_prev; /* Chain of loaded objects.  */

    /* All following members are internal to the dynamic linker.
       They may change without notice.  */

    /* This is an element which is only ever different from a pointer to
       the very same copy of this type for ld.so when it is used in more
       than one namespace.  */
    struct link_map *l_real;

    /* Number of the namespace this link map belongs to.  */
    Lmid_t l_ns;

    struct libname_list *l_libname;
    /* Indexed pointers to dynamic section.
       [0,DT_NUM) are indexed by the processor-independent tags.
       [DT_NUM,DT_NUM+DT_THISPROCNUM) are indexed by the tag minus DT_LOPROC.
       [DT_NUM+DT_THISPROCNUM,DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM) are
       indexed by DT_VERSIONTAGIDX(tagvalue).
       [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM,
	DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM) are indexed by
       DT_EXTRATAGIDX(tagvalue).
       [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM,
	DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM) are
       indexed by DT_VALTAGIDX(tagvalue) and
       [DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM,
	DT_NUM+DT_THISPROCNUM+DT_VERSIONTAGNUM+DT_EXTRANUM+DT_VALNUM+DT_ADDRNUM)
       are indexed by DT_ADDRTAGIDX(tagvalue), see <elf.h>.  */

    ElfW(Dyn) *l_info[DT_NUM + DT_THISPROCNUM + DT_VERSIONTAGNUM
		      + DT_EXTRANUM + DT_VALNUM + DT_ADDRNUM];
    const ElfW(Phdr) *l_phdr;	/* Pointer to program header table in core.  */
    ElfW(Addr) l_entry;		/* Entry point location.  */
    ElfW(Half) l_phnum;		/* Number of program header entries.  */
    ElfW(Half) l_ldnum;		/* Number of dynamic segment entries.  */

    /* Array of DT_NEEDED dependencies and their dependencies, in
       dependency order for symbol lookup (with and without
       duplicates).  There is no entry before the dependencies have
       been loaded.  */
    struct r_scope_elem l_searchlist;

    /* We need a special searchlist to process objects marked with
       DT_SYMBOLIC.  */
    struct r_scope_elem l_symbolic_searchlist;

    /* Dependent object that first caused this object to be loaded.  */
    struct link_map *l_loader;

    /* Array with version names.  */
    struct r_found_version *l_versions;
    unsigned int l_nversions;

    /* Symbol hash table.  */
    Elf_Symndx l_nbuckets;
    Elf32_Word l_gnu_bitmask_idxbits;
    Elf32_Word l_gnu_shift;
    const ElfW(Addr) *l_gnu_bitmask;
    union
    {
      const Elf32_Word *l_gnu_buckets;
      const Elf_Symndx *l_chain;
    };
    union
    {
      const Elf32_Word *l_gnu_chain_zero;
      const Elf_Symndx *l_buckets;
    };

    unsigned int l_direct_opencount; /* Reference count for dlopen/dlclose.  */
    enum			/* Where this object came from.  */
      {
	lt_executable,		/* The main executable program.  */
	lt_library,		/* Library needed by main executable.  */
	lt_loaded		/* Extra run-time loaded shared object.  */
      } l_type:2;
    unsigned int l_dt_relr_ref:1; /* Nonzero if GLIBC_ABI_DT_RELR is
				     referenced.  */
    unsigned int l_relocated:1;	/* Nonzero if object's relocations done.  */
    unsigned int l_init_called:1; /* Nonzero if DT_INIT function called.  */
    unsigned int l_global:1;	/* Nonzero if object in _dl_global_scope.  */
    unsigned int l_reserved:2;	/* Reserved for internal use.  */
    unsigned int l_main_map:1;  /* Nonzero for the map of the main program.  */
    unsigned int l_visited:1;   /* Used internally for map dependency
				   graph traversal.  */
    unsigned int l_map_used:1;  /* These two bits are used during traversal */
    unsigned int l_map_done:1;  /* of maps in _dl_close_worker. */
    unsigned int l_phdr_allocated:1; /* Nonzero if the data structure pointed
					to by `l_phdr' is allocated.  */
    unsigned int l_soname_added:1; /* Nonzero if the SONAME is for sure in
				      the l_libname list.  */
    unsigned int l_faked:1;	/* Nonzero if this is a faked descriptor
				   without associated file.  */
    unsigned int l_need_tls_init:1; /* Nonzero if GL(dl_init_static_tls)
				       should be called on this link map
				       when relocation finishes.  */
    unsigned int l_auditing:1;	/* Nonzero if the DSO is used in auditing.  */
    unsigned int l_audit_any_plt:1; /* Nonzero if at least one audit module
				       is interested in the PLT interception.*/
    unsigned int l_removed:1;	/* Nozero if the object cannot be used anymore
				   since it is removed.  */
    unsigned int l_contiguous:1; /* Nonzero if inter-segment holes are
				    mprotected or if no holes are present at
				    all.  */
    unsigned int l_free_initfini:1; /* Nonzero if l_initfini can be
				       freed, ie. not allocated with
				       the dummy malloc in ld.so.  */
    unsigned int l_ld_readonly:1; /* Nonzero if dynamic section is readonly.  */
    unsigned int l_find_object_processed:1; /* Zero if _dl_find_object_update
					       needs to process this
					       lt_library map.  */
    unsigned int l_tls_in_slotinfo:1; /* TLS slotinfo updated in dlopen.  */

    /* NODELETE status of the map.  Only valid for maps of type
       lt_loaded.  Lazy binding sets l_nodelete_active directly,
       potentially from signal handlers.  Initial loading of an
       DF_1_NODELETE object set l_nodelete_pending.  Relocation may
       set l_nodelete_pending as well.  l_nodelete_pending maps are
       promoted to l_nodelete_active status in the final stages of
       dlopen, prior to calling ELF constructors.  dlclose only
       refuses to unload l_nodelete_active maps, the pending status is
       ignored.  */
    bool l_nodelete_active;
    bool l_nodelete_pending;

#include <link_map.h>

    /* Collected information about own RPATH directories.  */
    struct r_search_path_struct l_rpath_dirs;

    /* Collected results of relocation while profiling.  */
    struct reloc_result
    {
      DL_FIXUP_VALUE_TYPE addr;
      struct link_map *bound;
      unsigned int boundndx;
      uint32_t enterexit;
      unsigned int flags;
      /* CONCURRENCY NOTE: This is used to guard the concurrent initialization
	 of the relocation result across multiple threads.  See the more
	 detailed notes in elf/dl-runtime.c.  */
      unsigned int init;
    } *l_reloc_result;

    /* Pointer to the version information if available.  */
    ElfW(Versym) *l_versyms;

    /* String specifying the path where this object was found.  */
    const char *l_origin;

    /* Start and finish of memory map for this object.  l_map_start
       need not be the same as l_addr.  */
    ElfW(Addr) l_map_start, l_map_end;

    /* Default array for 'l_scope'.  */
    struct r_scope_elem *l_scope_mem[4];
    /* Size of array allocated for 'l_scope'.  */
    size_t l_scope_max;
    /* This is an array defining the lookup scope for this link map.
       There are initially at most three different scope lists.  */
    struct r_scope_elem **l_scope;

    /* A similar array, this time only with the local scope.  This is
       used occasionally.  */
    struct r_scope_elem *l_local_scope[2];

    /* This information is kept to check for sure whether a shared
       object is the same as one already loaded.  */
    struct r_file_id l_file_id;

    /* Collected information about own RUNPATH directories.  */
    struct r_search_path_struct l_runpath_dirs;

    /* List of object in order of the init and fini calls.  */
    struct link_map **l_initfini;

    /* List of the dependencies introduced through symbol binding.  */
    struct link_map_reldeps
      {
	unsigned int act;
	struct link_map *list[];
      } *l_reldeps;
    unsigned int l_reldepsmax;

    /* Nonzero if the DSO is used.  */
    unsigned int l_used;

    /* Various flag words.  */
    ElfW(Word) l_feature_1;
    ElfW(Word) l_flags_1;
    ElfW(Word) l_flags;

    /* Temporarily used in `dl_close'.  */
    int l_idx;

    struct link_map_machine l_mach;

    struct
    {
      const ElfW(Sym) *sym;
      int type_class;
      struct link_map *value;
      const ElfW(Sym) *ret;
    } l_lookup_cache;

    /* Thread-local storage related info.  */

    /* Start of the initialization image.  */
    void *l_tls_initimage;
    /* Size of the initialization image.  */
    size_t l_tls_initimage_size;
    /* Size of the TLS block.  */
    size_t l_tls_blocksize;
    /* Alignment requirement of the TLS block.  */
    size_t l_tls_align;
    /* Offset of first byte module alignment.  */
    size_t l_tls_firstbyte_offset;
#ifndef NO_TLS_OFFSET
# define NO_TLS_OFFSET	0
#endif
#ifndef FORCED_DYNAMIC_TLS_OFFSET
# if NO_TLS_OFFSET == 0
#  define FORCED_DYNAMIC_TLS_OFFSET -1
# elif NO_TLS_OFFSET == -1
#  define FORCED_DYNAMIC_TLS_OFFSET -2
# else
#  error "FORCED_DYNAMIC_TLS_OFFSET is not defined"
# endif
#endif
    /* For objects present at startup time: offset in the static TLS block.  */
    ptrdiff_t l_tls_offset;
    /* Index of the module in the dtv array.  */
    size_t l_tls_modid;

    /* Number of thread_local objects constructed by this DSO.  This is
       atomically accessed and modified and is not always protected by the load
       lock.  See also: CONCURRENCY NOTES in cxa_thread_atexit_impl.c.  */
    size_t l_tls_dtor_count;

    /* Information used to change permission after the relocations are
       done.  */
    ElfW(Addr) l_relro_addr;
    size_t l_relro_size;

    unsigned long long int l_serial;
  };

#include <dl-relocate-ld.h>

/* Information used by audit modules.  For most link maps, this data
   immediate follows the link map in memory.  For the dynamic linker,
   it is allocated separately.  See link_map_audit_state in
   <ldsodefs.h>.  */
struct auditstate
{
  uintptr_t cookie;
  unsigned int bindflags;
};


/* This is the hidden instance of struct r_debug_extended used by the
   dynamic linker.  */
extern struct r_debug_extended _r_debug_extended attribute_hidden;

#if __ELF_NATIVE_CLASS == 32
# define symbind symbind32
# define LA_SYMBIND "la_symbind32"
#elif __ELF_NATIVE_CLASS == 64
# define symbind symbind64
# define LA_SYMBIND "la_symbind64"
#else
# error "__ELF_NATIVE_CLASS must be defined"
#endif

extern int __dl_iterate_phdr (int (*callback) (struct dl_phdr_info *info,
					       size_t size, void *data),
			      void *data);
hidden_proto (__dl_iterate_phdr)

/* We use this macro to refer to ELF macros independent of the native
   wordsize.  `ELFW(R_TYPE)' is used in place of `ELF32_R_TYPE' or
   `ELF64_R_TYPE'.  */
#define ELFW(type)	_ElfW (ELF, __ELF_NATIVE_CLASS, type)

# endif /* !_ISOMAC */
#endif /* include/link.h */