/*      $NetBSD: rtld.c,v 1.226 2026/07/01 19:31:15 riastradh Exp $      */

/*
 * Copyright 1996 John D. Polstra.
 * Copyright 1996 Matt Thomas <matt@3am-software.com>
 * Copyright 2002 Charles M. Hannum <root@ihack.net>
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. All advertising materials mentioning features or use of this software
 *    must display the following acknowledgement:
 *      This product includes software developed by John Polstra.
 * 4. The name of the author may not be used to endorse or promote products
 *    derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/*
 * Dynamic linker for ELF.
 *
 * John Polstra <jdp@polstra.com>.
 */

#include <sys/cdefs.h>
#ifndef lint
__RCSID("$NetBSD: rtld.c,v 1.226 2026/07/01 19:31:15 riastradh Exp $");
#endif /* not lint */

#include <sys/param.h>
#include <sys/atomic.h>
#include <sys/mman.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <lwp.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <dirent.h>

#include <ctype.h>

#include <dlfcn.h>

#include "debug.h"
#include "hash.h"
#include "rtld.h"

#if !defined(lint)
#include "sysident.h"
#endif

/*
 * Hidden function from common/lib/libc/atomic - nop on machines
 * with enough atomic ops. Need to explicitly call it early.
 * libc has the same symbol and will initialize itself, but not our copy.
 */
void __libc_atomic_init(void);

/*
 * Function declarations.
 */
static void     _rtld_init(caddr_t, caddr_t, const char *);
static void     _rtld_exit(void);

Elf_Addr        _rtld(Elf_Addr *, Elf_Addr);


/*
 * Data declarations.
 */
static char    *error_message;  /* Message for dlopen(), or NULL */

struct r_debug  _rtld_debug;    /* The SVR4 interface for the debugger */
bool            _rtld_trust;    /* False for setuid and setgid programs */
Obj_Entry      *_rtld_objlist;  /* Head of linked list of shared objects */
Obj_Entry     **_rtld_objtail;  /* Link field of last object in list */
Obj_Entry      *_rtld_objmain;  /* The main program shared object */
Obj_Entry       _rtld_objself;  /* The dynamic linker shared object */
u_int           _rtld_objcount; /* Number of objects in _rtld_objlist */
u_int           _rtld_objrelocpending = 1; /* Number of objects pending reloc */
u_int           _rtld_objloads; /* Number of objects loaded in _rtld_objlist */
u_int           _rtld_objgen;   /* Generation count for _rtld_objlist */
const char      _rtld_path[] = _PATH_RTLD;

/* Initialize a fake symbol for resolving undefined weak references. */
Elf_Sym         _rtld_sym_zero = {
    .st_info    = ELF_ST_INFO(STB_GLOBAL, STT_NOTYPE),
    .st_shndx   = SHN_ABS,
};
size_t  _rtld_pagesz;   /* Page size, as provided by kernel */

Search_Path    *_rtld_default_paths;
Search_Path    *_rtld_paths;

Library_Xform  *_rtld_xforms;
static void    *auxinfo;

/*
 * Global declarations normally provided by crt0.
 */
char           *__progname;
char          **environ;

static volatile bool _rtld_mutex_may_recurse;

#if defined(RTLD_DEBUG)
#ifndef __sh__
extern Elf_Addr _GLOBAL_OFFSET_TABLE_[];
#else  /* 32-bit SuperH */
register Elf_Addr *_GLOBAL_OFFSET_TABLE_ asm("r12");
#endif
#endif /* RTLD_DEBUG */
extern Elf_Dyn  _DYNAMIC;

static void _rtld_call_fini_functions(sigset_t *, int);
static void _rtld_call_init_functions(sigset_t *);
static void _rtld_call_preinit_functions(sigset_t *);
static void _rtld_initlist_visit(Objlist *, Obj_Entry *, int);
static void _rtld_initlist_tsort(Objlist *, int);
static Obj_Entry *_rtld_dlcheck(void *);
static void _rtld_init_dag(Obj_Entry *);
static void _rtld_init_dag1(Obj_Entry *, Obj_Entry *);
static void _rtld_objlist_remove(Objlist *, Obj_Entry *);
static void _rtld_objlist_clear(Objlist *);
static void _rtld_unload_object(sigset_t *, Obj_Entry *, bool);
static void _rtld_unref_dag(Obj_Entry *);
static Obj_Entry *_rtld_obj_from_addr(const void *);
static void _rtld_fill_dl_phdr_info(const Obj_Entry *, struct dl_phdr_info *);

/*
 * _rtld_load_needed_enter(obj)
 *
 *      Mark obj as busy loading its dependencies.  Multiple threads
 *      may be working on a single thread's dependencies concurrently;
 *      dlclose will wait until they are all done.  Caller must follow
 *      this by _rtld_load_needed_enter.
 *
 *      Non-reentrant: a thread must not call this again until it has
 *      called _rtld_load_needed_exit.
 *
 *      Caller must hold the rtld exclusive lock.  obj must have
 *      positive refcount; if it is already slated for destruction,
 *      this is not useful.
 */
void
_rtld_load_needed_enter(Obj_Entry *obj)
{

        assert(obj->refcount > 0);
        assert(obj->neededrefcount < INT_MAX);
        obj->neededrefcount++;
}

/*
 * _rtld_load_needed_exit(obj)
 *
 *      Mark obj as no longer busy loading its dependencies after
 *      _rtld_load_needed_enter.
 *
 *      Caller must hold the rtld exclusive lock.  Will not release or
 *      reacquire it.
 *
 *      Caller must have previously called
 *      _rtld_loadingneeded_enter(obj, ...) in the same thread.
 */
void
_rtld_load_needed_exit(Obj_Entry *obj)
{

        assert(obj->neededrefcount > 0);

        if (__predict_false(--obj->neededrefcount))
                return;
        if (__predict_true(obj->neededwaiter == 0))
                return;
        assert(obj->refcount == 0);
        _lwp_unpark(obj->neededwaiter, &obj->neededrefcount);
        obj->neededwaiter = 0;
}

/*
 * _rtld_wait_for_load_needed(&obj, mask)
 *
 *      If another thread is concurrently loading obj's dependencies,
 *      release the rtld exclusive lock, wait until it is done,
 *      reacquire the rtld exclusive lock, and return true.  On
 *      return, obj is nulled out.
 *
 *      Otherwise, if there is no thread concurrently loading obj's
 *      dependencies, leave it intact and return false without
 *      releasing and reacquiring the rtld exclusive lock -- obj is
 *      safe to free now.
 *
 *      Caller must hold the rtld exclusive lock.  May release and
 *      reacquire the rtld exclusive lock.  obj must have refcount zero
 *      already; this is only for when we are preparing to free obj.
 */
static bool
_rtld_wait_for_load_needed(Obj_Entry **objp, sigset_t *mask)
{
        Obj_Entry *obj = *objp;
        lwpid_t next;

        /*
         * This is only useful when obj is already marked for
         * destruction.
         */
        assert(obj->refcount == 0);

        /*
         * If there are no threads concurrently loading obj's
         * dependencies, nothing to do.
         */
        if (__predict_true(obj->neededrefcount == 0))
                return false;

        /*
         * Queue ourselves up to be notified when all threads are done
         * loading obj's dependencies, and remember the next thread to
         * be notified.
         */
        next = obj->neededwaiter;
        obj->neededwaiter = _lwp_self();

        /*
         * Release the rtld exclusive lock to wait and reacquire it
         * when done.  After we release the lock, we can't dereference
         * obj -- it may be concurrently freed by dlclose.
         */
        _rtld_exclusive_exit(mask);
        *objp = NULL;
        _lwp_park(CLOCK_REALTIME, 0, NULL, 0, &obj->neededrefcount, NULL);
        _rtld_exclusive_enter(mask);

        /*
         * If another thread was waiting too, notify that thread.
         */
        if (next)
                _lwp_unpark(next, &obj->neededrefcount);

        /*
         * Notify the caller that we released/reacquired the rtld
         * exclusive lock to wait for a state change so they must start
         * over from the top.
         */
        return true;
}

/*
 * _rtld_initfini_enter(&obj, mask)
 *
 *      Prepare to call an init/fini routine and return true if the
 *      caller should do it and then call _rtld_initfini_exit, or false
 *      if we waited for a state change and the caller must start over
 *      from the top.
 *
 *      If another thread is concurrently running an init/fini routine
 *      for the same object, release the rtld exclusive lock, wait
 *      until it's done (or a spurious wakeup), reacquire the rtld
 *      exclusive lock, null out obj, and return false.  Returning
 *      false does _not_ imply the init/fini is done -- it only implies
 *      that it _may_ be done but the caller must reassess the rtld
 *      state and start over from the top.
 *
 *      Otherwise, mark obj as running an init/fini routine in this
 *      thread and return true, without releasing and reacquiring the
 *      rtld exclusive lock.
 *
 *      Caller must hold the rtld exclusive lock.  May release and
 *      reacquire the rtld exclusive lock.
 */
static bool
_rtld_initfini_enter(Obj_Entry **objp, sigset_t *mask)
{
        Obj_Entry *obj = *objp;
        lwpid_t next;

        /*
         * If no other thread is concurrently running an init/fini
         * routine for this object, claim the object for this thread
         * and return true without releasing or reacquiring the rtld
         * exclusive lock.
         */
        if (__predict_true(obj->initfinilock == 0)) {
                obj->initfinilock = _lwp_self();
                return true;
        }

        /*
         * Remember whether anyone else is waiting for the lock, and
         * record ourselves as waiting.
         */
        next = obj->initfinilockwaiter;
        obj->initfinilockwaiter = _lwp_self();

        /*
         * Release the rtld exclusive lock, wait for a state change,
         * and reacquire the rtld exclusive lock.  Must not touch obj
         * after releasing the rtld exclusive lock -- it may be
         * concurrently freed by dlclose.
         */
        _rtld_exclusive_exit(mask);
        *objp = NULL;
        _lwp_park(CLOCK_REALTIME, 0, NULL, 0, &obj->initfinilock, NULL);
        _rtld_exclusive_enter(mask);

        /*
         * If anyone else was waiting for the lock, wake them too.
         */
        if (next)
                _lwp_unpark(next, &obj->initfinilock);

        /*
         * Notify the caller we failed to claim the object and
         * released/reacquired the lock to wait for a state change so
         * they must start over from the top.
         */
        return false;
}

/*
 * _rtld_initfini_exit(obj)
 *
 *      Mark obj as no longer running an init/fini routine in this
 *      thread, and wake any threads waiting for _rtld_initfini_enter
 *      on it.
 *
 *      Caller must hold the rtld exclusive lock.  Will not release or
 *      reacquire it.
 *
 *      Caller must have previously called _rtld_initfini_enter(&obj,
 *      ...) in the same thread, and it must have returned true.
 */
static void
_rtld_initfini_exit(Obj_Entry *obj)
{

        /*
         * We had better have claimed this object.  Relinquish our
         * claim.
         */
        assert(obj->initfinilock == _lwp_self());
        obj->initfinilock = 0;

        /*
         * If there's anyone waiting for the lock, wake them.  This may
         * provoke a thundering herd but it's unlikely that there will
         * be much contention on dlopen/dlclose in the real world.
         */
        if (__predict_true(obj->initfinilockwaiter == 0))
                return;
        _lwp_unpark(obj->initfinilockwaiter, &obj->initfinilock);
        obj->initfinilockwaiter = 0;
}

/*
 * _rtld_fini_done(obj)
 *
 *      Mark obj as done running destructors.  Wake any waiters in
 *      _rtld_wait_for_fini(&obj, ...).
 *
 *      Caller must hold the rtld exclusive lock.  Will not release or
 *      reacquire it.
 */
static void
_rtld_fini_done(Obj_Entry *obj)
{

        assert(obj->refcount == 0);
        if (__predict_true(obj->finiwaiter == 0))
                return;
        _lwp_unpark(obj->finiwaiter, &obj->refcount);
        obj->finiwaiter = 0;
}

/*
 * _rtld_wait_for_fini(&obj, mask)
 *
 *      If another thread is concurrently running destructors for obj,
 *      release the rtld exclusive lock, wait for that to complete,
 *      reacquire the rtld exclusive lock, and return true.  On return,
 *      obj is nulled out -- it was in the process of being destroyed
 *      when we started and it may be completely gone by the time we
 *      return.
 *
 *      Otherwise, if there is no thread concurrently running
 *      destructors for obj, leave it intact and return false without
 *      releasing and reacquiring the rtld exclusive lock -- obj is
 *      safe to use.
 *
 *      Caller must either hold the rtld exclusive lock, or be
 *      single-threaded; if single-threaded, this is guaranteed to
 *      return false, and mask may be null.
 */
bool
_rtld_wait_for_fini(Obj_Entry **objp, sigset_t *mask)
{
        Obj_Entry *obj = *objp;
        lwpid_t next;

        /*
         * If the object is still referenced, it can't be in the
         * process of destruction, so nothing to do -- notify the
         * caller we didn't wait.
         */
        if (__predict_true(obj->refcount > 0))
                return false;

        /*
         * We can only reach this point if there are threads running
         * dlopen or dlclose concurrently.  This can't happen during
         * initial program load -- pthread_create is not available for
         * use in a constructor -- so initial program load can skip
         * taking the rtld exclusive lock.
         */
        assert(mask != NULL);

        /*
         * Queue ourselves up to be notified when concurrent fini is
         * done, and remember the next thread to be notified.
         */
        next = obj->finiwaiter;
        obj->finiwaiter = _lwp_self();

        /*
         * Release the rtld exclusive lock to wait and reacquire it
         * when done.  After we release the lock, we can't dereference
         * obj -- it may be concurrently freed by dlclose.
         */
        _rtld_exclusive_exit(mask);
        *objp = NULL;
        _lwp_park(CLOCK_REALTIME, 0, NULL, 0, &obj->refcount, NULL);
        _rtld_exclusive_enter(mask);

        /*
         * If another thread was waiting too, notify that thread.
         */
        if (next)
                _lwp_unpark(next, &obj->refcount);

        /*
         * Notify the caller that we released/reacquired the rtld
         * exclusive lock to wait for a state change so they must start
         * over from the top.
         */
        return true;
}

static inline void
_rtld_call_initfini_function(fptr_t func, sigset_t *mask)
{
        _rtld_exclusive_exit(mask);
        (*func)();
        _rtld_exclusive_enter(mask);
}

static void
_rtld_call_fini_function(Obj_Entry *obj, sigset_t *mask, u_int cur_objgen)
{
        if (obj->fini_arraysz == 0 && (obj->fini == NULL || obj->fini_called))
                return;

        if (obj->fini != NULL && !obj->fini_called) {
                dbg (("calling fini function %s at %p%s", obj->path,
                    (void *)obj->fini,
                    obj->z_initfirst ? " (DF_1_INITFIRST)" : ""));
                obj->fini_called = 1;
                _rtld_call_initfini_function(obj->fini, mask);
        }
#ifdef HAVE_INITFINI_ARRAY
        /*
         * Now process the fini_array if it exists.  Simply go from
         * start to end.  We need to make restartable so just advance
         * the array pointer and decrement the size each time through
         * the loop.
         *
         * Paranoia: avoid touching obj if the generation has changed.
         */
        while (__predict_true(_rtld_objgen == cur_objgen) &&
            obj->fini_arraysz > 0) {
                fptr_t fini = *obj->fini_array++;
                obj->fini_arraysz--;
                dbg (("calling fini array function %s at %p%s", obj->path,
                    (void *)fini,
                    obj->z_initfirst ? " (DF_1_INITFIRST)" : ""));
                _rtld_call_initfini_function(fini, mask);
        }
#endif /* HAVE_INITFINI_ARRAY */
}

static void
_rtld_call_fini_functions(sigset_t *mask, int force)
{
        Objlist_Entry *elm;
        Objlist finilist;
        u_int cur_objgen;

        dbg(("_rtld_call_fini_functions(%d)", force));

restart:
        cur_objgen = _rtld_objgen;
        SIMPLEQ_INIT(&finilist);
        _rtld_initlist_tsort(&finilist, 1);

        /* First pass: objects _not_ marked with DF_1_INITFIRST. */
        SIMPLEQ_FOREACH(elm, &finilist, link) {
                Obj_Entry *obj = elm->obj;
                if (!obj->z_initfirst) {
                        if (obj->refcount > 0 && !force) {
                                continue;
                        }
                        if (!_rtld_initfini_enter(&obj, mask)) {
                                _rtld_objlist_clear(&finilist);
                                goto restart;
                        }
                        _rtld_call_fini_function(obj, mask, cur_objgen);
                        _rtld_initfini_exit(obj);
                        if (_rtld_objgen != cur_objgen) {
                                dbg(("restarting fini iteration"));
                                _rtld_objlist_clear(&finilist);
                                goto restart;
                        }
                }
        }

        /* Second pass: objects marked with DF_1_INITFIRST. */
        SIMPLEQ_FOREACH(elm, &finilist, link) {
                Obj_Entry *obj = elm->obj;
                if (obj->refcount > 0 && !force) {
                        continue;
                }
                if (!_rtld_initfini_enter(&obj, mask)) {
                        _rtld_objlist_clear(&finilist);
                        goto restart;
                }
                _rtld_call_fini_function(obj, mask, cur_objgen);
                _rtld_initfini_exit(obj);
                if (_rtld_objgen != cur_objgen) {
                        dbg(("restarting fini iteration"));
                        _rtld_objlist_clear(&finilist);
                        goto restart;
                }
        }

        _rtld_objlist_clear(&finilist);
}

static void
_rtld_call_init_function(Obj_Entry *obj, sigset_t *mask, u_int cur_objgen)
{
        if (obj->init_arraysz == 0 && (obj->init_called || obj->init == NULL))
                return;

        if (!obj->init_called && obj->init != NULL) {
                dbg (("calling init function %s at %p%s",
                    obj->path, (void *)obj->init,
                    obj->z_initfirst ? " (DF_1_INITFIRST)" : ""));
                obj->init_called = 1;
                _rtld_call_initfini_function(obj->init, mask);
        }

#ifdef HAVE_INITFINI_ARRAY
        /*
         * Now process the init_array if it exists.  Simply go from
         * start to end.  We need to make restartable so just advance
         * the array pointer and decrement the size each time through
         * the loop.
         */
        while (obj->init_arraysz > 0 && _rtld_objgen == cur_objgen) {
                fptr_t init = *obj->init_array++;
                obj->init_arraysz--;
                dbg (("calling init_array function %s at %p%s",
                    obj->path, (void *)init,
                    obj->z_initfirst ? " (DF_1_INITFIRST)" : ""));
                _rtld_call_initfini_function(init, mask);
        }
#endif /* HAVE_INITFINI_ARRAY */
}

static bool
_rtld_call_ifunc_functions(sigset_t *mask, Obj_Entry *obj, u_int cur_objgen)
{
        if (!_rtld_initfini_enter(&obj, mask))
                return true;
        if (obj->ifunc_remaining
#if defined(IFUNC_NONPLT)
            || obj->ifunc_remaining_nonplt
#endif
        ) {
                _rtld_call_ifunc(obj, mask, cur_objgen);
                if (_rtld_objgen != cur_objgen) {
                        _rtld_initfini_exit(obj);
                        return true;
                }
        }
        _rtld_initfini_exit(obj);
        return false;
}

static void
_rtld_call_preinit_functions(sigset_t *mask)
{
#ifdef HAVE_INITFINI_ARRAY
        Obj_Entry      *obj = _rtld_objmain;

        /*
         * Process the init_array if it exists.  Simply go from  start
         * to end.
         */
        for (size_t i = 0; i < obj->preinit_arraysz; i++) {
                fptr_t preinit = obj->preinit_array[i];
                dbg (("calling preinit_array function %s at %p",
                    obj->path, (void *)preinit));
                _rtld_call_initfini_function(preinit, mask);
        }
#endif /* HAVE_INITFINI_ARRAY */
}

static void
_rtld_call_init_functions(sigset_t *mask)
{
        Objlist_Entry *elm;
        Objlist initlist;
        u_int cur_objgen;

        dbg(("_rtld_call_init_functions()"));

restart:
        cur_objgen = _rtld_objgen;
        SIMPLEQ_INIT(&initlist);
        _rtld_initlist_tsort(&initlist, 0);

        /* First pass: objects with IRELATIVE relocations. */
        SIMPLEQ_FOREACH(elm, &initlist, link) {
                Obj_Entry *obj = elm->obj;
                if (__predict_false(_rtld_wait_for_fini(&obj, mask))) {
                        _rtld_objlist_clear(&initlist);
                        goto restart;
                }
                if (_rtld_call_ifunc_functions(mask, obj, cur_objgen)) {
                        dbg(("restarting init iteration"));
                        _rtld_objlist_clear(&initlist);
                        goto restart;
                }
        }
        /*
         * XXX: For historic reasons, init/fini of the main object are called
         * from crt0. Don't introduce that mistake for ifunc, so look at
         * the head of _rtld_objlist that _rtld_initlist_tsort skipped.
         */
        assert(_rtld_objlist->refcount != 0);
        if (_rtld_call_ifunc_functions(mask, _rtld_objlist, cur_objgen)) {
                dbg(("restarting init iteration"));
                _rtld_objlist_clear(&initlist);
                goto restart;
        }

        /* Second pass: objects marked with DF_1_INITFIRST. */
        SIMPLEQ_FOREACH(elm, &initlist, link) {
                Obj_Entry *obj = elm->obj;
                if (__predict_false(_rtld_wait_for_fini(&obj, mask))) {
                        _rtld_objlist_clear(&initlist);
                        goto restart;
                }
                if (obj->z_initfirst) {
                        if (!_rtld_initfini_enter(&obj, mask)) {
                                _rtld_objlist_clear(&initlist);
                                goto restart;
                        }
                        _rtld_call_init_function(obj, mask, cur_objgen);
                        _rtld_initfini_exit(obj);
                        if (_rtld_objgen != cur_objgen) {
                                dbg(("restarting init iteration"));
                                _rtld_objlist_clear(&initlist);
                                goto restart;
                        }
                }
        }

        /* Third pass: all other objects. */
        SIMPLEQ_FOREACH(elm, &initlist, link) {
                Obj_Entry *obj = elm->obj;
                if (__predict_false(_rtld_wait_for_fini(&obj, mask))) {
                        _rtld_objlist_clear(&initlist);
                        goto restart;
                }
                if (!_rtld_initfini_enter(&obj, mask)) {
                        _rtld_objlist_clear(&initlist);
                        goto restart;
                }
                _rtld_call_init_function(obj, mask, cur_objgen);
                _rtld_initfini_exit(obj);
                if (_rtld_objgen != cur_objgen) {
                        dbg(("restarting init iteration"));
                        _rtld_objlist_clear(&initlist);
                        goto restart;
                }
        }

        _rtld_objlist_clear(&initlist);
}

/*
 * Initialize the dynamic linker.  The argument is the address at which
 * the dynamic linker has been mapped into memory.  The primary task of
 * this function is to create an Obj_Entry for the dynamic linker and
 * to resolve the PLT relocation for platforms that need it (those that
 * define __HAVE_FUNCTION_DESCRIPTORS
 */
static void
_rtld_init(caddr_t mapbase, caddr_t relocbase, const char *execname)
{
        const Elf_Ehdr *ehdr;

        /* Conjure up an Obj_Entry structure for the dynamic linker. */
        _rtld_objself.path = __UNCONST(_rtld_path);
        _rtld_objself.pathlen = sizeof(_rtld_path)-1;
        _rtld_objself.rtld = true;
        _rtld_objself.mapbase = mapbase;
        _rtld_objself.relocbase = relocbase;
        _rtld_objself.dynamic = (Elf_Dyn *) &_DYNAMIC;
        _rtld_objself.strtab = "_rtld_sym_zero";

        /*
         * Set value to -relocbase so that
         *
         *     _rtld_objself.relocbase + _rtld_sym_zero.st_value == 0
         *
         * This allows unresolved references to weak symbols to be computed
         * to a value of 0.
         */
        _rtld_sym_zero.st_value = -(uintptr_t)relocbase;

        _rtld_digest_dynamic(_rtld_path, &_rtld_objself);
        assert(!_rtld_objself.needed);
#if !defined(__hppa__)
        assert(!_rtld_objself.pltrel && !_rtld_objself.pltrela);
#else
        _rtld_relocate_plt_objects(&_rtld_objself);
#endif
#if !defined(__mips__) && !defined(__hppa__)
        assert(!_rtld_objself.pltgot);
#endif
#if !defined(__arm__) && !defined(__mips__) && !defined(__sh__)
        /* ARM, MIPS and SH{3,5} have a bogus DT_TEXTREL. */
        assert(!_rtld_objself.textrel);
#endif

        _rtld_add_paths(execname, &_rtld_default_paths,
            RTLD_DEFAULT_LIBRARY_PATH);

#ifdef RTLD_ARCH_SUBDIR
        _rtld_add_paths(execname, &_rtld_default_paths,
            RTLD_DEFAULT_LIBRARY_PATH "/" RTLD_ARCH_SUBDIR);
#endif

        /* Make the object list empty. */
        _rtld_objlist = NULL;
        _rtld_objtail = &_rtld_objlist;
        _rtld_objcount = 0;

        _rtld_debug.r_version = R_DEBUG_VERSION;
        _rtld_debug.r_brk = _rtld_debug_state;
        _rtld_debug.r_state = RT_CONSISTENT;
        _rtld_debug.r_ldbase = _rtld_objself.relocbase;

        ehdr = (Elf_Ehdr *)mapbase;
        _rtld_objself.phdr = (Elf_Phdr *)((char *)mapbase + ehdr->e_phoff);
        _rtld_objself.phsize = ehdr->e_phnum * sizeof(_rtld_objself.phdr[0]);

        __libc_atomic_init();
}

/*
 * Cleanup procedure.  It will be called (by the atexit() mechanism) just
 * before the process exits.
 */
static void
_rtld_exit(void)
{
        sigset_t mask;

        dbg(("rtld_exit()"));

        _rtld_exclusive_enter(&mask);

        _rtld_call_fini_functions(&mask, 1);

        _rtld_exclusive_exit(&mask);
}

__dso_public void *
_dlauxinfo(void)
{
        return auxinfo;
}

/*
 * Main entry point for dynamic linking.  The argument is the stack
 * pointer.  The stack is expected to be laid out as described in the
 * SVR4 ABI specification, Intel 386 Processor Supplement.  Specifically,
 * the stack pointer points to a word containing ARGC.  Following that
 * in the stack is a null-terminated sequence of pointers to argument
 * strings.  Then comes a null-terminated sequence of pointers to
 * environment strings.  Finally, there is a sequence of "auxiliary
 * vector" entries.
 *
 * This function returns the entry point for the main program, the dynamic
 * linker's exit procedure in sp[0], and a pointer to the main object in
 * sp[1].
 */
Elf_Addr
_rtld(Elf_Addr *sp, Elf_Addr relocbase)
{
        const AuxInfo  *pAUX_base, *pAUX_entry, *pAUX_execfd, *pAUX_phdr,
                       *pAUX_phent, *pAUX_phnum, *pAUX_euid, *pAUX_egid,
                       *pAUX_ruid, *pAUX_rgid;
        const AuxInfo  *pAUX_pagesz;
        char          **env, **oenvp;
        const AuxInfo  *auxp;
        Obj_Entry      *obj;
        Elf_Addr       *const osp = sp;
        bool            bind_now = 0;
        const char     *ld_bind_now, *ld_preload, *ld_library_path;
        const char    **argv;
        const char     *execname, *objmain_name;
        long            argc;
        const char **real___progname;
        const Obj_Entry **real___mainprog_obj;
        char ***real_environ;
        sigset_t        mask;
#ifdef DEBUG
        const char     *ld_debug;
#endif
#ifdef RTLD_DEBUG
        int i = 0;
#endif

        /*
         * On entry, the dynamic linker itself has not been relocated yet.
         * Be very careful not to reference any global data until after
         * _rtld_init has returned.  It is OK to reference file-scope statics
         * and string constants, and to call static and global functions.
         */
        /* Find the auxiliary vector on the stack. */
        /* first Elf_Word reserved to address of exit routine */
#if defined(RTLD_DEBUG)
        debug = 1;
        dbg(("sp = %p, argc = %ld, argv = %p <%s> relocbase %p", sp,
            (long)sp[2], &sp[3], (char *) sp[3], (void *)relocbase));
#ifndef __x86_64__
        dbg(("got is at %p, dynamic is at %p", _GLOBAL_OFFSET_TABLE_,
            &_DYNAMIC));
#endif
#endif

        sp += 2;                /* skip over return argument space */
        argv = (const char **) &sp[1];
        argc = *(long *)sp;
        sp += 2 + argc;         /* Skip over argc, arguments, and NULL
                                 * terminator */
        env = (char **) sp;
        while (*sp++ != 0) {    /* Skip over environment, and NULL terminator */
#if defined(RTLD_DEBUG)
                dbg(("env[%d] = %p %s", i++, (void *)sp[-1], (char *)sp[-1]));
#endif
        }
        auxinfo = (AuxInfo *) sp;

        pAUX_base = pAUX_entry = pAUX_execfd = NULL;
        pAUX_phdr = pAUX_phent = pAUX_phnum = NULL;
        pAUX_euid = pAUX_ruid = pAUX_egid = pAUX_rgid = NULL;
        pAUX_pagesz = NULL;

        execname = NULL;

        /* Digest the auxiliary vector. */
        for (auxp = auxinfo; auxp->a_type != AT_NULL; ++auxp) {
                switch (auxp->a_type) {
                case AT_BASE:
                        pAUX_base = auxp;
                        break;
                case AT_ENTRY:
                        pAUX_entry = auxp;
                        break;
                case AT_EXECFD:
                        pAUX_execfd = auxp;
                        break;
                case AT_PHDR:
                        pAUX_phdr = auxp;
                        break;
                case AT_PHENT:
                        pAUX_phent = auxp;
                        break;
                case AT_PHNUM:
                        pAUX_phnum = auxp;
                        break;
#ifdef AT_EUID
                case AT_EUID:
                        pAUX_euid = auxp;
                        break;
                case AT_RUID:
                        pAUX_ruid = auxp;
                        break;
                case AT_EGID:
                        pAUX_egid = auxp;
                        break;
                case AT_RGID:
                        pAUX_rgid = auxp;
                        break;
#endif
#ifdef AT_SUN_EXECNAME
                case AT_SUN_EXECNAME:
                        execname = (const char *)(const void *)auxp->a_v;
                        break;
#endif
                case AT_PAGESZ:
                        pAUX_pagesz = auxp;
                        break;
                }
        }

        /* Initialize and relocate ourselves. */
        if (pAUX_base == NULL) {
                _rtld_error("Bad pAUX_base");
                _rtld_die();
        }
        assert(pAUX_pagesz != NULL);
        _rtld_pagesz = (int)pAUX_pagesz->a_v;
        _rtld_init((caddr_t)pAUX_base->a_v, (caddr_t)relocbase, execname);

        __progname = _rtld_objself.path;
        environ = env;

        _rtld_trust = ((pAUX_euid ? (uid_t)pAUX_euid->a_v : geteuid()) ==
            (pAUX_ruid ? (uid_t)pAUX_ruid->a_v : getuid())) &&
            ((pAUX_egid ? (gid_t)pAUX_egid->a_v : getegid()) ==
            (pAUX_rgid ? (gid_t)pAUX_rgid->a_v : getgid()));

#ifdef DEBUG
        ld_debug = NULL;
#endif
        ld_bind_now = NULL;
        ld_library_path = NULL;
        ld_preload = NULL;
        /*
         * Inline avoid using normal getenv/unsetenv here as the libc
         * code is quite a bit more complicated.
         */
        for (oenvp = env; *env != NULL; ++env) {
                static const char bind_var[] = "LD_BIND_NOW=";
                static const char debug_var[] =  "LD_DEBUG=";
                static const char path_var[] = "LD_LIBRARY_PATH=";
                static const char preload_var[] = "LD_PRELOAD=";
#define LEN(x)  (sizeof(x) - 1)

                if ((*env)[0] != 'L' || (*env)[1] != 'D') {
                        /*
                         * Special case to skip most entries without
                         * the more expensive calls to strncmp.
                         */
                        *oenvp++ = *env;
                } else if (strncmp(*env, debug_var, LEN(debug_var)) == 0) {
                        if (_rtld_trust) {
#ifdef DEBUG
                                ld_debug = *env + LEN(debug_var);
#endif
                                *oenvp++ = *env;
                        }
                } else if (strncmp(*env, bind_var, LEN(bind_var)) == 0) {
                        if (_rtld_trust) {
                                ld_bind_now = *env + LEN(bind_var);
                                *oenvp++ = *env;
                        }
                } else if (strncmp(*env, path_var, LEN(path_var)) == 0) {
                        if (_rtld_trust) {
                                ld_library_path = *env + LEN(path_var);
                                *oenvp++ = *env;
                        }
                } else if (strncmp(*env, preload_var, LEN(preload_var)) == 0) {
                        if (_rtld_trust) {
                                ld_preload = *env + LEN(preload_var);
                                *oenvp++ = *env;
                        }
                } else {
                        *oenvp++ = *env;
                }
#undef LEN
        }
        *oenvp++ = NULL;

        /*
         * Set the main name. Prefer the name passed by the kernel first,
         * then the argument vector, and fall back to "main program"
         * This way the name will be an absolute path if available.
         */
        objmain_name = execname ? execname :
            (argv[0] ? argv[0] : "main program");

        if (ld_bind_now != NULL && *ld_bind_now != '\0')
                bind_now = true;
        if (_rtld_trust) {
#ifdef DEBUG
#ifdef RTLD_DEBUG
                debug = 0;
#endif
                if (ld_debug != NULL && *ld_debug != '\0')
                        debug = 1;
#endif
                _rtld_add_paths(execname, &_rtld_paths, ld_library_path);
        } else {
                // Prevent $ORIGIN expansion
                execname = NULL;
        }
        _rtld_process_hints(execname, &_rtld_paths, &_rtld_xforms,
            _PATH_LD_HINTS);
        dbg(("dynamic linker is initialized, mapbase=%p, relocbase=%p",
             _rtld_objself.mapbase, _rtld_objself.relocbase));

        /*
         * Load the main program, or process its program header if it is
         * already loaded.
         */
        if (pAUX_execfd != NULL) {      /* Load the main program. */
                int             fd = pAUX_execfd->a_v;
                dbg(("loading main program"));
                _rtld_objmain = _rtld_map_object(objmain_name, fd, NULL);
                close(fd);
                if (_rtld_objmain == NULL)
                        _rtld_die();
        } else {                /* Main program already loaded. */
                const Elf_Phdr *phdr;
                int             phnum;
                caddr_t         entry;

                dbg(("processing main program's program header"));
                assert(pAUX_phdr != NULL);
                phdr = (const Elf_Phdr *) pAUX_phdr->a_v;
                assert(pAUX_phnum != NULL);
                phnum = pAUX_phnum->a_v;
                assert(pAUX_phent != NULL);
                assert(pAUX_phent->a_v == sizeof(Elf_Phdr));
                assert(pAUX_entry != NULL);
                entry = (caddr_t) pAUX_entry->a_v;
                _rtld_objmain = _rtld_digest_phdr(phdr, phnum, entry);
                _rtld_objmain->path = xstrdup(objmain_name);
                _rtld_objmain->pathlen = strlen(_rtld_objmain->path);
        }

        _rtld_objmain->mainprog = true;

        /*
         * Get the actual dynamic linker pathname from the executable if
         * possible.  (It should always be possible.)  That ensures that
         * the debugger will find the right dynamic linker even if a
         * non-standard one is being used.
         */
        if (_rtld_objmain->interp != NULL &&
            strcmp(_rtld_objmain->interp, _rtld_objself.path) != 0) {
                _rtld_objself.path = xstrdup(_rtld_objmain->interp);
                _rtld_objself.pathlen = strlen(_rtld_objself.path);
        }
        dbg(("actual dynamic linker is %s", _rtld_objself.path));

        _rtld_digest_dynamic(execname, _rtld_objmain);

        /* Link the main program into the list of objects. */
        *_rtld_objtail = _rtld_objmain;
        _rtld_objtail = &_rtld_objmain->next;
        _rtld_objcount++;
        _rtld_objloads++;

        _rtld_linkmap_add(_rtld_objmain);
        _rtld_objself.path = xstrdup(_rtld_objself.path);
        _rtld_linkmap_add(&_rtld_objself);

        ++_rtld_objmain->refcount;
        _rtld_objmain->mainref = 1;
        _rtld_objlist_push_tail(&_rtld_list_main, _rtld_objmain);

        if (ld_preload) {
                /*
                 * Pre-load user-specified objects after the main program
                 * but before any shared object dependencies.
                 */
                dbg(("preloading objects"));
                if (_rtld_preload(ld_preload, NULL) == -1)
                        _rtld_die();
        }

        dbg(("loading needed objects"));
        if (_rtld_load_needed_objects(_rtld_objmain, _RTLD_MAIN, NULL) == -1)
                _rtld_die();

        dbg(("checking for required versions"));
        for (obj = _rtld_objlist; obj != NULL; obj = obj->next) {
                if (_rtld_verify_object_versions(obj) == -1)
                        _rtld_die();
        }

#if defined(__HAVE_TLS_VARIANT_I) || defined(__HAVE_TLS_VARIANT_II)
        dbg(("initializing initial Thread Local Storage offsets"));
        /*
         * All initial objects get the TLS space from the static block.
         */
        for (obj = _rtld_objlist; obj != NULL; obj = obj->next)
                _rtld_tls_offset_allocate(obj);
#endif

        dbg(("relocating objects"));
        if (_rtld_relocate_objects(_rtld_objmain, bind_now) == -1)
                _rtld_die();

        dbg(("doing copy relocations"));
        if (_rtld_do_copy_relocations(_rtld_objmain) == -1)
                _rtld_die();

#if defined(__HAVE_TLS_VARIANT_I) || defined(__HAVE_TLS_VARIANT_II)
        dbg(("initializing Thread Local Storage for main thread"));
        /*
         * Set up TLS area for the main thread.
         * This has to be done after all relocations are processed,
         * since .tdata may contain relocations.
         */
        _rtld_tls_initial_allocation();
#endif

        /*
         * Set the __progname,  environ and, __mainprog_obj before
         * calling anything that might use them.
         */
        real___progname = _rtld_objmain_sym("__progname");
        if (real___progname) {
                if (argv[0] != NULL) {
                        if ((*real___progname = strrchr(argv[0], '/')) == NULL)
                                (*real___progname) = argv[0];
                        else
                                (*real___progname)++;
                } else {
                        (*real___progname) = NULL;
                }
        }
        real_environ = _rtld_objmain_sym("environ");
        if (real_environ)
                *real_environ = environ;
        /*
         * Set __mainprog_obj for old binaries.
         */
        real___mainprog_obj = _rtld_objmain_sym("__mainprog_obj");
        if (real___mainprog_obj)
                *real___mainprog_obj = _rtld_objmain;

        _rtld_debug_state();    /* say hello to the debugger! */

        _rtld_exclusive_enter(&mask);

        dbg(("calling main preinit array functions"));
        _rtld_call_preinit_functions(&mask);

        dbg(("calling _init functions"));
        _rtld_call_init_functions(&mask);

        dbg(("control at program entry point = %p, obj = %p, exit = %p",
             _rtld_objmain->entry, _rtld_objmain, _rtld_exit));

        _rtld_exclusive_exit(&mask);

#ifdef GNU_RELRO
        /*
         * If the main program is lazily bound (default -- whether or
         * not LD_BINDNOW is set in the calling environment), its RELRO
         * region has already been mapped read-only in
         * _rtld_do_copy_relocations.  The ifunc resolutions lie
         * outside this region, so future lazy ifunc resolution is
         * unaffected by the RELRO region's being read-only.
         *
         * If the main program is eagerly bound (i.e., the object has
         * DF_1_NOW set in DT_FLAGS_1, whether or not LD_BIND_NOW is
         * set in the calling environment), we deferred that from
         * _rtld_do_copy_relocations so that the ifunc resolution, we
         * have now resolved all ifuncs in it, so we can commit the
         * RELRO region to be read-only -- and that means ifunc
         * resolutions are read-only too.
         */
        if (_rtld_objmain->z_now && _rtld_relro(_rtld_objmain, true) == -1)
                _rtld_die();
#endif

        /*
         * Return with the entry point and the exit procedure in at the top
         * of stack.
         */

        ((void **) osp)[0] = _rtld_exit;
        ((void **) osp)[1] = __UNCONST(_rtld_compat_obj);
        return (Elf_Addr) _rtld_objmain->entry;
}

void
_rtld_die(void)
{
        const char *msg = dlerror();

        if (msg == NULL)
                msg = "Fatal error";
        xerrx(1, "%s", msg);
}

static Obj_Entry *
_rtld_dlcheck(void *handle)
{
        Obj_Entry *obj;

        for (obj = _rtld_objlist; obj != NULL; obj = obj->next)
                if (obj == (Obj_Entry *) handle)
                        break;

        if (obj == NULL || obj->dl_refcount == 0) {
                _rtld_error("Invalid shared object handle %p", handle);
                return NULL;
        }
        return obj;
}

static void
_rtld_initlist_visit(Objlist* list, Obj_Entry *obj, int rev)
{
        Needed_Entry* elm;

        /* dbg(("_rtld_initlist_visit(%s)", obj->path)); */

        /*
         * If the object hasn't been relocated yet, we have nothing to
         * do -- another thread is running dlopen, and will get to it
         * eventually, but it isn't ordered with respect to any
         * initializers we have to run.
         */
        if (!obj->relocated)
                return;

        /*
         * If the object has already been visited, we have nothing to
         * do, so skip it.  Note: This is reset at the beginning of
         * _rtld_initlist_topsort; it does not reflect whether the
         * initializers have actually run yet.
         */
        if (obj->init_done)
                return;
        obj->init_done = 1;

        for (elm = obj->needed; elm != NULL; elm = elm->next) {
                if (elm->obj != NULL) {
                        _rtld_initlist_visit(list, elm->obj, rev);
                }
        }

        if (rev) {
                _rtld_objlist_push_head(list, obj);
        } else {
                _rtld_objlist_push_tail(list, obj);
        }
}

static void
_rtld_initlist_tsort(Objlist* list, int rev)
{
        dbg(("_rtld_initlist_tsort"));

        Obj_Entry* obj;

        /*
         * We don't include objmain here (starting from next)
         * because csu handles it
         */
        for (obj = _rtld_objlist->next; obj; obj = obj->next) {
                obj->init_done = 0;
        }

        for (obj = _rtld_objlist->next; obj; obj = obj->next) {
                _rtld_initlist_visit(list, obj, rev);
        }
}

static void
_rtld_init_dag(Obj_Entry *root)
{

        _rtld_init_dag1(root, root);
}

static void
_rtld_init_dag1(Obj_Entry *root, Obj_Entry *obj)
{
        const Needed_Entry *needed;

        if (!obj->mainref) {
                if (_rtld_objlist_find(&obj->dldags, root))
                        return;
                dbg(("add %p (%s) to %p (%s) DAG", obj, obj->path, root,
                    root->path));
                _rtld_objlist_push_tail(&obj->dldags, root);
                _rtld_objlist_push_tail(&root->dagmembers, obj);
        }
        for (needed = obj->needed; needed != NULL; needed = needed->next)
                if (needed->obj != NULL)
                        _rtld_init_dag1(root, needed->obj);
}

/*
 * Note, this is called only for objects loaded by dlopen().
 */
static void
_rtld_unload_object(sigset_t *mask, Obj_Entry *root, bool do_fini_funcs)
{

        _rtld_unref_dag(root);
        if (root->refcount == 0) { /* We are finished with some objects. */
                Obj_Entry *obj;
                Obj_Entry **linkp;
                Objlist_Entry *elm;

                assert(root->dl_refcount == 0);
                assert(!root->z_nodelete);
                assert(!root->ref_nodel);

                /*
                 * A concurrent dlopen of some other library might have
                 * picked up this object while loading needed entries.
                 * Wait for that to complete.  The root can't go away
                 * at this point: we already hold the last actual
                 * reference to it.
                 */
                obj = root;
                (void)_rtld_wait_for_load_needed(&obj, mask);
                assert(root->refcount == 0);
                assert(root->dl_refcount == 0);
                assert(!root->z_nodelete);
                assert(!root->ref_nodel);

                /*
                 * Finalize objects that are about to be unmapped.  Set
                 * root->dlclosing while we do this so concurrent
                 * dlclose calls, which can run while the rtld
                 * exclusive lock is dropped across fini calls, will
                 * skip this when garbage-collecting the object list.
                 */
                if (do_fini_funcs) {
                        root->dlclosing = true;
                        _rtld_call_fini_functions(mask, 0);
                        assert(root->dlclosing);
                        assert(root->refcount == 0);
                        assert(root->dl_refcount == 0);
                        root->dlclosing = false;
                }

                /* Remove the DAG from all objects' DAG lists. */
                SIMPLEQ_FOREACH(elm, &root->dagmembers, link)
                        _rtld_objlist_remove(&elm->obj->dldags, root);

                /* Remove the DAG from the RTLD_GLOBAL list. */
                if (root->globalref) {
                        root->globalref = 0;
                        _rtld_objlist_remove(&_rtld_list_global, root);
                }

                /*
                 * Unmap all objects that are no longer referenced.
                 *
                 * Objects that are unreferenced but have dlclosing or
                 * initfinilock set must be in use in a concurrent call
                 * to _rtld_unload_object, which will go through the
                 * list of objects to unmap when it is done, so we skip
                 * them -- this avoids pulling the rug out from under
                 * the concurrent call, and won't leak.
                 *
                 * For objects that are still having their dependencies
                 * loaded, we have to wait until the loading is done --
                 * and while we're waiting, another thread might free
                 * it, so we have to start over from the top.
                 */
restart:
                linkp = &_rtld_objlist->next;
                while ((obj = *linkp) != NULL) {
                        if (obj->refcount == 0 &&
                            !obj->dlclosing &&
                            obj->initfinilock == 0) {
                                if (__predict_false(
                                    _rtld_wait_for_load_needed(&obj, mask)))
                                        goto restart;
                                dbg(("unloading \"%s\"", obj->path));
                                if (obj->ehdr != MAP_FAILED)
                                        munmap(obj->ehdr, _rtld_pagesz);
                                munmap(obj->mapbase, obj->mapsize);
                                _rtld_objlist_remove(&_rtld_list_global, obj);
                                _rtld_linkmap_delete(obj);
                                *linkp = obj->next;
                                _rtld_objcount--;
                                _rtld_fini_done(obj);
                                _rtld_obj_free(obj);
                        } else
                                linkp = &obj->next;
                }
                _rtld_objtail = linkp;
                _rtld_objgen++;
        }
}

void
_rtld_ref_dag(Obj_Entry *root)
{
        const Needed_Entry *needed;

        assert(root);
        assert(root->refcount > 0);

        ++root->refcount;

        dbg(("incremented reference on \"%s\" (%d)", root->path,
            root->refcount));
        for (needed = root->needed; needed != NULL;
             needed = needed->next) {
                if (needed->obj != NULL)
                        _rtld_ref_dag(needed->obj);
        }
}

static void
_rtld_unref_dag(Obj_Entry *root)
{

        assert(root);
        assert(root->refcount != 0);

        --root->refcount;
        dbg(("decremented reference on \"%s\" (%d)", root->path,
            root->refcount));

        if (root->refcount == 0) {
                const Needed_Entry *needed;

                for (needed = root->needed; needed != NULL;
                     needed = needed->next) {
                        if (needed->obj != NULL)
                                _rtld_unref_dag(needed->obj);
                }
        }
}

__strong_alias(__dlclose,dlclose)
int
dlclose(void *handle)
{
        Obj_Entry *root;
        sigset_t mask;

        dbg(("dlclose of %p", handle));

        _rtld_exclusive_enter(&mask);

        root = _rtld_dlcheck(handle);

        if (root == NULL) {
                _rtld_exclusive_exit(&mask);
                return -1;
        }
        assert(root->refcount != 0);
        assert(root->dl_refcount != 0);

        _rtld_debug.r_state = RT_DELETE;
        _rtld_debug_state();

        --root->dl_refcount;
        assert(root->refcount != 0);
        _rtld_unload_object(&mask, root, true);

        _rtld_debug.r_state = RT_CONSISTENT;
        _rtld_debug_state();

        _rtld_exclusive_exit(&mask);

        return 0;
}

__strong_alias(__dlerror,dlerror)
char *
dlerror(void)
{
        char *msg = error_message;

        error_message = NULL;
        return msg;
}

__strong_alias(__dlopen,dlopen)
void *
dlopen(const char *name, int mode)
{
        Obj_Entry *obj = NULL;
        int flags = _RTLD_DLOPEN;
        bool nodelete;
        bool now;
        sigset_t mask;
        int result;

        dbg(("dlopen of %s 0x%x", name, mode));

        _rtld_exclusive_enter(&mask);

        flags |= (mode & RTLD_GLOBAL) ? _RTLD_GLOBAL : 0;
        flags |= (mode & RTLD_NOLOAD) ? _RTLD_NOLOAD : 0;

        nodelete = (mode & RTLD_NODELETE) ? true : false;
        now = ((mode & RTLD_MODEMASK) == RTLD_NOW) ? true : false;

        _rtld_debug.r_state = RT_ADD;
        _rtld_debug_state();

        if (name == NULL) {
                obj = _rtld_objmain;
                assert(obj->refcount > 0);
                obj->refcount++;
        } else
                obj = _rtld_load_library(name, _rtld_objmain, flags, &mask);

        if (obj != NULL) {
                assert(obj->refcount > 0);
                ++obj->dl_refcount;
                if (_rtld_objrelocpending) {    /* We loaded something new. */
                        result = _rtld_load_needed_objects(obj, flags, &mask);
                        if (result != -1) {
                                Objlist_Entry *entry;
                                _rtld_init_dag(obj);
                                SIMPLEQ_FOREACH(entry, &obj->dagmembers, link) {
                                        result = _rtld_verify_object_versions(entry->obj);
                                        if (result == -1)
                                                break;
                                }
                        }
                        if (result == -1 || _rtld_relocate_objects(_rtld_objlist,
                            (now || obj->z_now)) == -1) {
                                obj->dl_refcount--;
                                _rtld_unload_object(&mask, obj, false);
                                obj = NULL;
                        } else {
                                _rtld_call_init_functions(&mask);
                        }
                }
                if (obj != NULL) {
                        if ((nodelete || obj->z_nodelete) && !obj->ref_nodel) {
                                dbg(("dlopen obj %s nodelete", obj->path));
                                _rtld_ref_dag(obj);
                                obj->z_nodelete = obj->ref_nodel = true;
                        }
                }
        }
        _rtld_debug.r_state = RT_CONSISTENT;
        _rtld_debug_state();

        dbg(("dlopen of %s 0x%x returned %p%s%s%s", name, mode, obj,
            obj ? "" : " (", obj ? "" : error_message, obj ? "" : ")"));

        _rtld_exclusive_exit(&mask);

        return obj;
}

/*
 * Find a symbol in the main program.
 */
_Pragma("GCC diagnostic push")  /* _rtld_donelist_init: -Wno-stack-protector */
_Pragma("GCC diagnostic ignored \"-Wstack-protector\"")
void *
_rtld_objmain_sym(const char *name)
{
        Elf_Hash hash;
        const Elf_Sym *def;
        const Obj_Entry *obj;
        DoneList donelist;

        hash.sysv = _rtld_sysv_hash(name);
        hash.gnu = _rtld_gnu_hash(name);
        obj = _rtld_objmain;
        _rtld_donelist_init(&donelist);

        def = _rtld_symlook_list(name, &hash, &_rtld_list_main, &obj, 0,
            NULL, &donelist);

        if (def != NULL)
                return obj->relocbase + def->st_value;
        return NULL;
}
_Pragma("GCC diagnostic pop")

#if defined(__powerpc__) && !defined(__clang__)
static __noinline void *
hackish_return_address(void)
{
#if __GNUC_PREREQ__(6,0)
#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wframe-address"
#endif
        return __builtin_return_address(1);
#if __GNUC_PREREQ__(6,0)
#pragma GCC diagnostic pop
#endif
}
#endif

#ifdef __HAVE_FUNCTION_DESCRIPTORS
#define lookup_mutex_enter()    _rtld_exclusive_enter(&mask)
#define lookup_mutex_exit()     _rtld_exclusive_exit(&mask)
#else
#define lookup_mutex_enter()    _rtld_shared_enter()
#define lookup_mutex_exit()     _rtld_shared_exit()
#endif

_Pragma("GCC diagnostic push")  /* _rtld_donelist_init: -Wno-stack-protector */
_Pragma("GCC diagnostic ignored \"-Wstack-protector\"")
static void *
do_dlsym(void *handle, const char *name, const Ver_Entry *ventry, void *retaddr)
{
        const Obj_Entry *obj;
        Elf_Hash hash;
        const Elf_Sym *def;
        const Obj_Entry *defobj;
        DoneList donelist;
        const u_int flags = SYMLOOK_DLSYM | SYMLOOK_IN_PLT;
#ifdef __HAVE_FUNCTION_DESCRIPTORS
        sigset_t mask;
#endif

        lookup_mutex_enter();

        hash.sysv = _rtld_sysv_hash(name);
        hash.gnu = _rtld_gnu_hash(name);
        def = NULL;
        defobj = NULL;

        switch ((intptr_t)handle) {
        case (intptr_t)NULL:
        case (intptr_t)RTLD_NEXT:
        case (intptr_t)RTLD_DEFAULT:
        case (intptr_t)RTLD_SELF:
                if ((obj = _rtld_obj_from_addr(retaddr)) == NULL) {
                        _rtld_error("Cannot determine caller's shared object");
                        lookup_mutex_exit();
                        return NULL;
                }

                switch ((intptr_t)handle) {
                case (intptr_t)NULL:     /* Just the caller's shared object. */
                        def = _rtld_symlook_obj(name, &hash, obj, flags, ventry);
                        defobj = obj;
                        break;

                case (intptr_t)RTLD_NEXT:       /* Objects after callers */
                        obj = obj->next;
                        /*FALLTHROUGH*/

                case (intptr_t)RTLD_SELF:       /* Caller included */
                        for (; obj; obj = obj->next) {
                                if ((def = _rtld_symlook_obj(name, &hash, obj,
                                    flags, ventry)) != NULL) {
                                        defobj = obj;
                                        break;
                                }
                        }
                        /*
                         * Search the dynamic linker itself, and possibly
                         * resolve the symbol from there if it is not defined
                         * already or weak. This is how the application links
                         * to dynamic linker services such as dlopen.
                         */
                        if (!def || ELF_ST_BIND(def->st_info) == STB_WEAK) {
                                const Elf_Sym *symp = _rtld_symlook_obj(name,
                                    &hash, &_rtld_objself, flags, ventry);
                                if (symp != NULL) {
                                        def = symp;
                                        defobj = &_rtld_objself;
                                }
                        }
                        break;

                case (intptr_t)RTLD_DEFAULT:
                        def = _rtld_symlook_default(name, &hash, obj, &defobj,
                            flags, ventry);
                        break;

                default:
                        abort();
                }
                break;

        default:
                if ((obj = _rtld_dlcheck(handle)) == NULL) {
                        lookup_mutex_exit();
                        return NULL;
                }

                _rtld_donelist_init(&donelist);

                if (obj->mainprog) {
                        /* Search main program and all libraries loaded by it */
                        def = _rtld_symlook_list(name, &hash, &_rtld_list_main,
                            &defobj, flags, ventry, &donelist);
                } else {
                        Needed_Entry fake;
                        DoneList depth;

                        /* Search the object and all the libraries loaded by it. */
                        fake.next = NULL;
                        fake.obj = __UNCONST(obj);
                        fake.name = 0;

                        _rtld_donelist_init(&depth);
                        def = _rtld_symlook_needed(name, &hash, &fake, &defobj,
                            flags, ventry, &donelist, &depth);
                }

                break;
        }

        if (def != NULL) {
                void *p;

                if (ELF_ST_TYPE(def->st_info) == STT_GNU_IFUNC) {
#ifdef __HAVE_FUNCTION_DESCRIPTORS
                        lookup_mutex_exit();
                        _rtld_shared_enter();
#endif
                        p = (void *)_rtld_resolve_ifunc(defobj, def);
                        _rtld_shared_exit();
                        return p;
                }

#ifdef __HAVE_FUNCTION_DESCRIPTORS
                if (ELF_ST_TYPE(def->st_info) == STT_FUNC) {
                        p = (void *)_rtld_function_descriptor_alloc(defobj,
                            def, 0);
                        lookup_mutex_exit();
                        return p;
                }
#endif /* __HAVE_FUNCTION_DESCRIPTORS */
                p = defobj->relocbase + def->st_value;
                lookup_mutex_exit();
                return p;
        }

        _rtld_error("Undefined symbol \"%s\"", name);
        lookup_mutex_exit();
        return NULL;
}
_Pragma("GCC diagnostic pop")

__strong_alias(__dlsym,dlsym)
void *
dlsym(void *handle, const char *name)
{
        void *retaddr;

        dbg(("dlsym of %s in %p", name, handle));

#if defined(__powerpc__) && !defined(__clang__)
        retaddr = hackish_return_address();
#else
        retaddr = __builtin_return_address(0);
#endif
        return do_dlsym(handle, name, NULL, retaddr);
}

__strong_alias(__dlvsym,dlvsym)
void *
dlvsym(void *handle, const char *name, const char *version)
{
        Ver_Entry *ventry = NULL;
        Ver_Entry ver_entry;
        void *retaddr;

        dbg(("dlvsym of %s@%s in %p", name, version ? version : NULL, handle));

        if (version != NULL) {
                ver_entry.name = version;
                ver_entry.file = NULL;
                ver_entry.hash = _rtld_sysv_hash(version);
                ver_entry.flags = 0;
                ventry = &ver_entry;
        }
#if defined(__powerpc__) && !defined(__clang__)
        retaddr = hackish_return_address();
#else
        retaddr = __builtin_return_address(0);
#endif
        return do_dlsym(handle, name, ventry, retaddr);
}

__strong_alias(__dladdr,dladdr)
int
dladdr(const void *addr, Dl_info *info)
{
        const Obj_Entry *obj;
        const Elf_Sym *def, *best_def;
        void *symbol_addr;
        unsigned long symoffset;
#ifdef __HAVE_FUNCTION_DESCRIPTORS
        sigset_t mask;
#endif

        dbg(("dladdr of %p", addr));

        lookup_mutex_enter();

#ifdef __HAVE_FUNCTION_DESCRIPTORS
        addr = _rtld_function_descriptor_function(addr);
#endif /* __HAVE_FUNCTION_DESCRIPTORS */

        obj = _rtld_obj_from_addr(addr);
        if (obj == NULL) {
                _rtld_error("No shared object contains address");
                lookup_mutex_exit();
                return 0;
        }
        info->dli_fname = obj->path;
        info->dli_fbase = obj->mapbase;
        info->dli_saddr = (void *)0;
        info->dli_sname = NULL;

        /*
         * Walk the symbol list looking for the symbol whose address is
         * closest to the address sent in.
         */
        best_def = NULL;
        for (symoffset = 0; symoffset < obj->nchains; symoffset++) {
                def = obj->symtab + symoffset;

                /*
                 * For skip the symbol if st_shndx is either SHN_UNDEF or
                 * SHN_COMMON.
                 */
                if (def->st_shndx == SHN_UNDEF || def->st_shndx == SHN_COMMON)
                        continue;

                /*
                 * If the symbol is greater than the specified address, or if it
                 * is further away from addr than the current nearest symbol,
                 * then reject it.
                 */
                symbol_addr = obj->relocbase + def->st_value;
                if (symbol_addr > addr || symbol_addr < info->dli_saddr)
                        continue;

                /* Update our idea of the nearest symbol. */
                info->dli_sname = obj->strtab + def->st_name;
                info->dli_saddr = symbol_addr;
                best_def = def;


                /* Exact match? */
                if (info->dli_saddr == addr)
                        break;
        }

#ifdef __HAVE_FUNCTION_DESCRIPTORS
        if (best_def != NULL && ELF_ST_TYPE(best_def->st_info) == STT_FUNC)
                info->dli_saddr = (void *)_rtld_function_descriptor_alloc(obj,
                    best_def, 0);
#else
        __USE(best_def);
#endif /* __HAVE_FUNCTION_DESCRIPTORS */

        lookup_mutex_exit();
        return 1;
}

__strong_alias(__dlinfo,dlinfo)
int
dlinfo(void *handle, int req, void *v)
{
        const Obj_Entry *obj;
        void *retaddr;

        dbg(("dlinfo for %p %d", handle, req));

        _rtld_shared_enter();

        if (handle == RTLD_SELF) {
#if defined(__powerpc__) && !defined(__clang__)
                retaddr = hackish_return_address();
#else
                retaddr = __builtin_return_address(0);
#endif
                if ((obj = _rtld_obj_from_addr(retaddr)) == NULL) {
                        _rtld_error("Cannot determine caller's shared object");
                        _rtld_shared_exit();
                        return -1;
                }
        } else {
                if ((obj = _rtld_dlcheck(handle)) == NULL) {
                        _rtld_shared_exit();
                        return -1;
                }
        }

        switch (req) {
        case RTLD_DI_LINKMAP:
                {
                const struct link_map **map = v;

                *map = &obj->linkmap;
                break;
                }

        default:
                _rtld_error("Invalid request");
                _rtld_shared_exit();
                return -1;
        }

        _rtld_shared_exit();
        return 0;
}

static void
_rtld_fill_dl_phdr_info(const Obj_Entry *obj, struct dl_phdr_info *phdr_info)
{

        phdr_info->dlpi_addr = (Elf_Addr)obj->relocbase;
        /* XXX: wrong but not fixing it yet */
        phdr_info->dlpi_name = obj->path;
        phdr_info->dlpi_phdr = obj->phdr;
        phdr_info->dlpi_phnum = obj->phsize / sizeof(obj->phdr[0]);
#if defined(__HAVE_TLS_VARIANT_I) || defined(__HAVE_TLS_VARIANT_II)
        phdr_info->dlpi_tls_modid = obj->tlsindex;
        phdr_info->dlpi_tls_data = obj->tlsinit;
#else
        phdr_info->dlpi_tls_modid = 0;
        phdr_info->dlpi_tls_data = 0;
#endif
        phdr_info->dlpi_adds = _rtld_objloads;
        phdr_info->dlpi_subs = _rtld_objloads - _rtld_objcount;
}

__strong_alias(__dl_iterate_phdr,dl_iterate_phdr);
int
dl_iterate_phdr(int (*callback)(struct dl_phdr_info *, size_t, void *), void *param)
{
        struct dl_phdr_info phdr_info;
        const Obj_Entry *obj;
        int error = 0;

        dbg(("dl_iterate_phdr"));

        _rtld_shared_enter();

        for (obj = _rtld_objlist;  obj != NULL;  obj = obj->next) {
                _rtld_fill_dl_phdr_info(obj, &phdr_info);

                /* XXXlocking: exit point */
                error = callback(&phdr_info, sizeof(phdr_info), param);
                if (error)
                        break;
        }

        if (error == 0) {
                _rtld_fill_dl_phdr_info(&_rtld_objself, &phdr_info);

                /* XXXlocking: exit point */
                error = callback(&phdr_info, sizeof(phdr_info), param);
        }

        _rtld_shared_exit();
        return error;
}

void
__dl_cxa_refcount(void *addr, ssize_t delta)
{
        sigset_t mask;
        Obj_Entry *obj;

        if (delta == 0)
                return;

        dbg(("__dl_cxa_refcount of %p with %zd", addr, delta));

        _rtld_exclusive_enter(&mask);
        obj = _rtld_obj_from_addr(addr);

        if (obj == NULL) {
                dbg(("__dl_cxa_refcont: address not found"));
                _rtld_error("No shared object contains address");
                _rtld_exclusive_exit(&mask);
                return;
        }
        if (delta > 0 && obj->cxa_refcount > SIZE_MAX - delta)
                _rtld_error("Reference count overflow");
        else if (delta < 0 && obj->cxa_refcount < -1 + (size_t)-(delta + 1))
                _rtld_error("Reference count underflow");
        else {
                if (obj->cxa_refcount == 0) {
                        assert(obj->refcount > 0);
                        ++obj->refcount;
                }
                obj->cxa_refcount += delta;
                dbg(("new reference count: %zu", obj->cxa_refcount));
                if (obj->cxa_refcount == 0) {
                        --obj->refcount;
                        if (obj->refcount == 0)
                                _rtld_unload_object(&mask, obj, true);
                }
        }

        _rtld_exclusive_exit(&mask);
}

__dso_public pid_t
__locked_fork(int *my_errno)
{
        pid_t result;

        _rtld_shared_enter();
        result = __fork();
        if (result == -1)
                *my_errno = errno;
        _rtld_shared_exit();

        return result;
}

/*
 * Error reporting function.  Use it like printf.  If formats the message
 * into a buffer, and sets things up so that the next call to dlerror()
 * will return the message.
 */
void
_rtld_error(const char *fmt,...)
{
        static char     buf[512];
        va_list         ap;

        va_start(ap, fmt);
        xvsnprintf(buf, sizeof buf, fmt, ap);
        dbg(("%s: %s", __func__, buf));
        error_message = buf;
        va_end(ap);
}

void
_rtld_debug_state(void)
{
#if defined(__hppa__)
        __asm volatile("nop" ::: "memory");
#endif

        /* Prevent optimizer from removing calls to this function */
        __insn_barrier();
}

void
_rtld_linkmap_add(Obj_Entry *obj)
{
        struct link_map *l = &obj->linkmap;
        struct link_map *prev;

        obj->linkmap.l_name = obj->path;
        obj->linkmap.l_addr = obj->relocbase;
        obj->linkmap.l_ld = obj->dynamic;
#ifdef __mips__
        /* XXX This field is not standard and will be removed eventually. */
        obj->linkmap.l_offs = obj->relocbase;
#endif

        if (_rtld_debug.r_map == NULL) {
                _rtld_debug.r_map = l;
                return;
        }

        /*
         * Scan to the end of the list, but not past the entry for the
         * dynamic linker, which we want to keep at the very end.
         */
        for (prev = _rtld_debug.r_map;
            prev->l_next != NULL && prev->l_next != &_rtld_objself.linkmap;
            prev = prev->l_next);

        l->l_prev = prev;
        l->l_next = prev->l_next;
        if (l->l_next != NULL)
                l->l_next->l_prev = l;
        prev->l_next = l;
}

void
_rtld_linkmap_delete(Obj_Entry *obj)
{
        struct link_map *l = &obj->linkmap;

        if (l->l_prev == NULL) {
                if ((_rtld_debug.r_map = l->l_next) != NULL)
                        l->l_next->l_prev = NULL;
                return;
        }
        if ((l->l_prev->l_next = l->l_next) != NULL)
                l->l_next->l_prev = l->l_prev;
}

static Obj_Entry *
_rtld_obj_from_addr(const void *addr)
{
        Obj_Entry *obj;

        for (obj = _rtld_objlist;  obj != NULL;  obj = obj->next) {
                if (addr < (void *) obj->mapbase)
                        continue;
                if (addr < (void *) (obj->mapbase + obj->mapsize))
                        return obj;
        }
        return NULL;
}

static void
_rtld_objlist_clear(Objlist *list)
{
        while (!SIMPLEQ_EMPTY(list)) {
                Objlist_Entry* elm = SIMPLEQ_FIRST(list);
                SIMPLEQ_REMOVE_HEAD(list, link);
                xfree(elm);
        }
}

static void
_rtld_objlist_remove(Objlist *list, Obj_Entry *obj)
{
        Objlist_Entry *elm;

        if ((elm = _rtld_objlist_find(list, obj)) != NULL) {
                SIMPLEQ_REMOVE(list, elm, Struct_Objlist_Entry, link);
                xfree(elm);
        }
}

#define RTLD_EXCLUSIVE_MASK     0x80000000U
static volatile unsigned int _rtld_mutex;
static volatile unsigned int _rtld_waiter_exclusive;
static volatile unsigned int _rtld_waiter_shared;

void
_rtld_shared_enter(void)
{
        unsigned int cur;
        lwpid_t waiter, self = 0;

        for (;;) {
                cur = _rtld_mutex;
                /*
                 * First check if we are currently not exclusively locked.
                 */
                if ((cur & RTLD_EXCLUSIVE_MASK) == 0) {
                        /* Yes, so increment use counter */
                        if (atomic_cas_uint(&_rtld_mutex, cur, cur + 1) != cur)
                                continue;
                        membar_acquire();
                        return;
                }
                /*
                 * Someone has an exclusive lock.  Puts us on the waiter list.
                 */
                if (!self)
                        self = _lwp_self();
                if (cur == (self | RTLD_EXCLUSIVE_MASK)) {
                        if (_rtld_mutex_may_recurse)
                                return;
                        _rtld_error("%s: dead lock detected", __func__);
                        _rtld_die();
                }
                waiter = atomic_swap_uint(&_rtld_waiter_shared, self);
                /*
                 * Check for race against _rtld_exclusive_exit before sleeping.
                 */
                membar_sync();
                if ((_rtld_mutex & RTLD_EXCLUSIVE_MASK) ||
                    _rtld_waiter_exclusive)
                        _lwp_park(CLOCK_REALTIME, 0, NULL, 0,
                            __UNVOLATILE(&_rtld_mutex), NULL);
                /* Try to remove us from the waiter list. */
                atomic_cas_uint(&_rtld_waiter_shared, self, 0);
                if (waiter)
                        _lwp_unpark(waiter, __UNVOLATILE(&_rtld_mutex));
        }
}

void
_rtld_shared_exit(void)
{
        lwpid_t waiter;

        /*
         * Shared lock taken after an exclusive lock.
         * Just assume this is a partial recursion.
         */
        if (_rtld_mutex & RTLD_EXCLUSIVE_MASK)
                return;

        /*
         * Wakeup LWPs waiting for an exclusive lock if this is the last
         * LWP on the shared lock.
         */
        membar_release();
        if (atomic_dec_uint_nv(&_rtld_mutex))
                return;
        membar_sync();
        if ((waiter = _rtld_waiter_exclusive) != 0)
                _lwp_unpark(waiter, __UNVOLATILE(&_rtld_mutex));
}

void
_rtld_exclusive_enter(sigset_t *mask)
{
        lwpid_t waiter, self = _lwp_self();
        unsigned int locked_value = (unsigned int)self | RTLD_EXCLUSIVE_MASK;
        unsigned int cur;
        sigset_t blockmask;

        sigfillset(&blockmask);
        sigdelset(&blockmask, SIGTRAP); /* Allow the debugger */
        sigprocmask(SIG_BLOCK, &blockmask, mask);

        for (;;) {
                if (atomic_cas_uint(&_rtld_mutex, 0, locked_value) == 0) {
                        membar_acquire();
                        break;
                }
                waiter = atomic_swap_uint(&_rtld_waiter_exclusive, self);
                membar_sync();
                cur = _rtld_mutex;
                if (cur == locked_value) {
                        _rtld_error("%s: dead lock detected", __func__);
                        _rtld_die();
                }
                if (cur)
                        _lwp_park(CLOCK_REALTIME, 0, NULL, 0,
                            __UNVOLATILE(&_rtld_mutex), NULL);
                atomic_cas_uint(&_rtld_waiter_exclusive, self, 0);
                if (waiter)
                        _lwp_unpark(waiter, __UNVOLATILE(&_rtld_mutex));
        }
}

void
_rtld_exclusive_exit(sigset_t *mask)
{
        lwpid_t waiter;

        membar_release();
        _rtld_mutex = 0;
        membar_sync();
        if ((waiter = _rtld_waiter_exclusive) != 0)
                _lwp_unpark(waiter, __UNVOLATILE(&_rtld_mutex));

        if ((waiter = _rtld_waiter_shared) != 0)
                _lwp_unpark(waiter, __UNVOLATILE(&_rtld_mutex));

        sigprocmask(SIG_SETMASK, mask, NULL);
}

int
_rtld_relro(const Obj_Entry *obj, bool wantmain)
{
#ifdef GNU_RELRO
        /*
         * If our VM page size is larger than the page size used by the
         * linker when laying out the object, we could end up making data
         * read-only that is unintended.  Detect and avoid this situation.
         * It may mean we are unable to protect everything we'd like, but
         * it's better than crashing.
         */
        uintptr_t relro_end = (uintptr_t)obj->relro_page + obj->relro_size;
        uintptr_t relro_start = round_down((uintptr_t)obj->relro_page);
        assert(relro_end >= relro_start);
        size_t relro_size = round_down(relro_end) - relro_start;

        if (relro_size == 0)
                return 0;
        if (wantmain != (obj ==_rtld_objmain))
                return 0;

        dbg(("RELRO %s %p %zx", obj->path, (void *)relro_start, relro_size));
        if (mprotect((void *)relro_start, relro_size, PROT_READ) == -1) {
                _rtld_error("%s: Cannot enforce relro " "protection: %s",
                    obj->path, xstrerror(errno));
                return -1;
        }
#endif
        return 0;
}