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freebsd-skq/libexec/rtld-elf/rtld.c
jdp 66a962ce67 Performance improvements for the ELF dynamic linker. These 
particularly help programs which load many shared libraries with
a lot of relocations.  Large C++ programs such as are found in KDE
are a prime example.

While relocating a shared object, maintain a vector of symbols
which have already been looked up, directly indexed by symbol
number.  Typically, symbols which are referenced by a relocation
entry are referenced by many of them.  This is the same optimization
I made to the a.out dynamic linker in 1995 (rtld.c revision 1.30).

Also, compare the first character of a sought-after symbol with its
symbol table entry before calling strcmp().

On a PII/400 these changes reduce the start-up time of a typical
KDE program from 833 msec (elapsed) to 370 msec.

MFC after:	5 days
2001-05-05 23:21:05 +00:00

2113 lines
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/*-
* Copyright 1996, 1997, 1998, 1999, 2000 John D. Polstra.
* 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.
*
* 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.
*
* $FreeBSD$
*/
/*
* Dynamic linker for ELF.
*
* John Polstra <jdp@polstra.com>.
*/
#ifndef __GNUC__
#error "GCC is needed to compile this file"
#endif
#include <sys/param.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <dlfcn.h>
#include <err.h>
#include <errno.h>
#include <fcntl.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include "debug.h"
#include "rtld.h"
#define END_SYM "_end"
#define PATH_RTLD "/usr/libexec/ld-elf.so.1"
/* Types. */
typedef void (*func_ptr_type)();
/*
* This structure provides a reentrant way to keep a list of objects and
* check which ones have already been processed in some way.
*/
typedef struct Struct_DoneList {
const Obj_Entry **objs; /* Array of object pointers */
unsigned int num_alloc; /* Allocated size of the array */
unsigned int num_used; /* Number of array slots used */
} DoneList;
/*
* Function declarations.
*/
static const char *basename(const char *);
static void die(void);
static void digest_dynamic(Obj_Entry *);
static Obj_Entry *digest_phdr(const Elf_Phdr *, int, caddr_t, const char *);
static Obj_Entry *dlcheck(void *);
static bool donelist_check(DoneList *, const Obj_Entry *);
static void errmsg_restore(char *);
static char *errmsg_save(void);
static char *find_library(const char *, const Obj_Entry *);
static const char *gethints(void);
static void init_dag(Obj_Entry *);
static void init_dag1(Obj_Entry *root, Obj_Entry *obj, DoneList *);
static void init_rtld(caddr_t);
static void initlist_add_neededs(Needed_Entry *needed, Objlist *list);
static void initlist_add_objects(Obj_Entry *obj, Obj_Entry **tail,
Objlist *list);
static bool is_exported(const Elf_Sym *);
static void linkmap_add(Obj_Entry *);
static void linkmap_delete(Obj_Entry *);
static int load_needed_objects(Obj_Entry *);
static int load_preload_objects(void);
static Obj_Entry *load_object(char *);
static void lock_check(void);
static Obj_Entry *obj_from_addr(const void *);
static void objlist_call_fini(Objlist *);
static void objlist_call_init(Objlist *);
static void objlist_clear(Objlist *);
static Objlist_Entry *objlist_find(Objlist *, const Obj_Entry *);
static void objlist_init(Objlist *);
static void objlist_push_head(Objlist *, Obj_Entry *);
static void objlist_push_tail(Objlist *, Obj_Entry *);
static void objlist_remove(Objlist *, Obj_Entry *);
static void objlist_remove_unref(Objlist *);
static int relocate_objects(Obj_Entry *, bool);
static void rtld_exit(void);
static char *search_library_path(const char *, const char *);
static void set_program_var(const char *, const void *);
static const Elf_Sym *symlook_default(const char *, unsigned long hash,
const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt);
static const Elf_Sym *symlook_list(const char *, unsigned long,
Objlist *, const Obj_Entry **, bool in_plt, DoneList *);
static void trace_loaded_objects(Obj_Entry *obj);
static void unload_object(Obj_Entry *);
static void unref_dag(Obj_Entry *);
void r_debug_state(struct r_debug*, struct link_map*);
void xprintf(const char *, ...);
/*
* Data declarations.
*/
static char *error_message; /* Message for dlerror(), or NULL */
struct r_debug r_debug; /* for GDB; */
static bool trust; /* False for setuid and setgid programs */
static char *ld_bind_now; /* Environment variable for immediate binding */
static char *ld_debug; /* Environment variable for debugging */
static char *ld_library_path; /* Environment variable for search path */
static char *ld_preload; /* Environment variable for libraries to
load first */
static char *ld_tracing; /* Called from ldd to print libs */
static Obj_Entry *obj_list; /* Head of linked list of shared objects */
static Obj_Entry **obj_tail; /* Link field of last object in list */
static Obj_Entry *obj_main; /* The main program shared object */
static Obj_Entry obj_rtld; /* The dynamic linker shared object */
static unsigned int obj_count; /* Number of objects in obj_list */
static Objlist list_global = /* Objects dlopened with RTLD_GLOBAL */
STAILQ_HEAD_INITIALIZER(list_global);
static Objlist list_main = /* Objects loaded at program startup */
STAILQ_HEAD_INITIALIZER(list_main);
static Objlist list_fini = /* Objects needing fini() calls */
STAILQ_HEAD_INITIALIZER(list_fini);
static LockInfo lockinfo;
static Elf_Sym sym_zero; /* For resolving undefined weak refs. */
#define GDB_STATE(s,m) r_debug.r_state = s; r_debug_state(&r_debug,m);
extern Elf_Dyn _DYNAMIC;
#pragma weak _DYNAMIC
/*
* These are the functions the dynamic linker exports to application
* programs. They are the only symbols the dynamic linker is willing
* to export from itself.
*/
static func_ptr_type exports[] = {
(func_ptr_type) &_rtld_error,
(func_ptr_type) &dlclose,
(func_ptr_type) &dlerror,
(func_ptr_type) &dlopen,
(func_ptr_type) &dlsym,
(func_ptr_type) &dladdr,
(func_ptr_type) &dllockinit,
NULL
};
/*
* Global declarations normally provided by crt1. The dynamic linker is
* not built with crt1, so we have to provide them ourselves.
*/
char *__progname;
char **environ;
/*
* Fill in a DoneList with an allocation large enough to hold all of
* the currently-loaded objects. Keep this as a macro since it calls
* alloca and we want that to occur within the scope of the caller.
*/
#define donelist_init(dlp) \
((dlp)->objs = alloca(obj_count * sizeof (dlp)->objs[0]), \
assert((dlp)->objs != NULL), \
(dlp)->num_alloc = obj_count, \
(dlp)->num_used = 0)
static __inline void
rlock_acquire(void)
{
lockinfo.rlock_acquire(lockinfo.thelock);
atomic_incr_int(&lockinfo.rcount);
lock_check();
}
static __inline void
wlock_acquire(void)
{
lockinfo.wlock_acquire(lockinfo.thelock);
atomic_incr_int(&lockinfo.wcount);
lock_check();
}
static __inline void
rlock_release(void)
{
atomic_decr_int(&lockinfo.rcount);
lockinfo.rlock_release(lockinfo.thelock);
}
static __inline void
wlock_release(void)
{
atomic_decr_int(&lockinfo.wcount);
lockinfo.wlock_release(lockinfo.thelock);
}
/*
* Main entry point for dynamic linking. The first 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.
*
* The second argument points to a place to store the dynamic linker's
* exit procedure pointer and the third to a place to store the main
* program's object.
*
* The return value is the main program's entry point.
*/
func_ptr_type
_rtld(Elf_Addr *sp, func_ptr_type *exit_proc, Obj_Entry **objp)
{
Elf_Auxinfo *aux_info[AT_COUNT];
int i;
int argc;
char **argv;
char **env;
Elf_Auxinfo *aux;
Elf_Auxinfo *auxp;
const char *argv0;
Obj_Entry *obj;
Obj_Entry **preload_tail;
Objlist initlist;
/*
* On entry, the dynamic linker itself has not been relocated yet.
* Be very careful not to reference any global data until after
* init_rtld 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. */
argc = *sp++;
argv = (char **) sp;
sp += argc + 1; /* Skip over arguments and NULL terminator */
env = (char **) sp;
while (*sp++ != 0) /* Skip over environment, and NULL terminator */
;
aux = (Elf_Auxinfo *) sp;
/* Digest the auxiliary vector. */
for (i = 0; i < AT_COUNT; i++)
aux_info[i] = NULL;
for (auxp = aux; auxp->a_type != AT_NULL; auxp++) {
if (auxp->a_type < AT_COUNT)
aux_info[auxp->a_type] = auxp;
}
/* Initialize and relocate ourselves. */
assert(aux_info[AT_BASE] != NULL);
init_rtld((caddr_t) aux_info[AT_BASE]->a_un.a_ptr);
__progname = obj_rtld.path;
argv0 = argv[0] != NULL ? argv[0] : "(null)";
environ = env;
trust = geteuid() == getuid() && getegid() == getgid();
ld_bind_now = getenv("LD_BIND_NOW");
if (trust) {
ld_debug = getenv("LD_DEBUG");
ld_library_path = getenv("LD_LIBRARY_PATH");
ld_preload = getenv("LD_PRELOAD");
}
ld_tracing = getenv("LD_TRACE_LOADED_OBJECTS");
if (ld_debug != NULL && *ld_debug != '\0')
debug = 1;
dbg("%s is initialized, base address = %p", __progname,
(caddr_t) aux_info[AT_BASE]->a_un.a_ptr);
dbg("RTLD dynamic = %p", obj_rtld.dynamic);
dbg("RTLD pltgot = %p", obj_rtld.pltgot);
/*
* Load the main program, or process its program header if it is
* already loaded.
*/
if (aux_info[AT_EXECFD] != NULL) { /* Load the main program. */
int fd = aux_info[AT_EXECFD]->a_un.a_val;
dbg("loading main program");
obj_main = map_object(fd, argv0, NULL);
close(fd);
if (obj_main == NULL)
die();
} else { /* Main program already loaded. */
const Elf_Phdr *phdr;
int phnum;
caddr_t entry;
dbg("processing main program's program header");
assert(aux_info[AT_PHDR] != NULL);
phdr = (const Elf_Phdr *) aux_info[AT_PHDR]->a_un.a_ptr;
assert(aux_info[AT_PHNUM] != NULL);
phnum = aux_info[AT_PHNUM]->a_un.a_val;
assert(aux_info[AT_PHENT] != NULL);
assert(aux_info[AT_PHENT]->a_un.a_val == sizeof(Elf_Phdr));
assert(aux_info[AT_ENTRY] != NULL);
entry = (caddr_t) aux_info[AT_ENTRY]->a_un.a_ptr;
if ((obj_main = digest_phdr(phdr, phnum, entry, argv0)) == NULL)
die();
}
obj_main->path = xstrdup(argv0);
obj_main->mainprog = true;
/*
* Get the actual dynamic linker pathname from the executable if
* possible. (It should always be possible.) That ensures that
* gdb will find the right dynamic linker even if a non-standard
* one is being used.
*/
if (obj_main->interp != NULL &&
strcmp(obj_main->interp, obj_rtld.path) != 0) {
free(obj_rtld.path);
obj_rtld.path = xstrdup(obj_main->interp);
}
digest_dynamic(obj_main);
linkmap_add(obj_main);
linkmap_add(&obj_rtld);
/* Link the main program into the list of objects. */
*obj_tail = obj_main;
obj_tail = &obj_main->next;
obj_count++;
obj_main->refcount++;
/* Make sure we don't call the main program's init and fini functions. */
obj_main->init = obj_main->fini = NULL;
/* Initialize a fake symbol for resolving undefined weak references. */
sym_zero.st_info = ELF_ST_INFO(STB_GLOBAL, STT_NOTYPE);
sym_zero.st_shndx = SHN_ABS;
dbg("loading LD_PRELOAD libraries");
if (load_preload_objects() == -1)
die();
preload_tail = obj_tail;
dbg("loading needed objects");
if (load_needed_objects(obj_main) == -1)
die();
/* Make a list of all objects loaded at startup. */
for (obj = obj_list; obj != NULL; obj = obj->next)
objlist_push_tail(&list_main, obj);
if (ld_tracing) { /* We're done */
trace_loaded_objects(obj_main);
exit(0);
}
if (relocate_objects(obj_main,
ld_bind_now != NULL && *ld_bind_now != '\0') == -1)
die();
dbg("doing copy relocations");
if (do_copy_relocations(obj_main) == -1)
die();
dbg("initializing key program variables");
set_program_var("__progname", argv[0] != NULL ? basename(argv[0]) : "");
set_program_var("environ", env);
dbg("initializing thread locks");
lockdflt_init(&lockinfo);
lockinfo.thelock = lockinfo.lock_create(lockinfo.context);
/* Make a list of init functions to call. */
objlist_init(&initlist);
initlist_add_objects(obj_list, preload_tail, &initlist);
r_debug_state(NULL, &obj_main->linkmap); /* say hello to gdb! */
objlist_call_init(&initlist);
wlock_acquire();
objlist_clear(&initlist);
wlock_release();
dbg("transferring control to program entry point = %p", obj_main->entry);
/* Return the exit procedure and the program entry point. */
*exit_proc = rtld_exit;
*objp = obj_main;
return (func_ptr_type) obj_main->entry;
}
Elf_Addr
_rtld_bind(Obj_Entry *obj, Elf_Word reloff)
{
const Elf_Rel *rel;
const Elf_Sym *def;
const Obj_Entry *defobj;
Elf_Addr *where;
Elf_Addr target;
rlock_acquire();
if (obj->pltrel)
rel = (const Elf_Rel *) ((caddr_t) obj->pltrel + reloff);
else
rel = (const Elf_Rel *) ((caddr_t) obj->pltrela + reloff);
where = (Elf_Addr *) (obj->relocbase + rel->r_offset);
def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true, NULL);
if (def == NULL)
die();
target = (Elf_Addr)(defobj->relocbase + def->st_value);
dbg("\"%s\" in \"%s\" ==> %p in \"%s\"",
defobj->strtab + def->st_name, basename(obj->path),
(void *)target, basename(defobj->path));
reloc_jmpslot(where, target);
rlock_release();
return target;
}
/*
* 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);
vsnprintf(buf, sizeof buf, fmt, ap);
error_message = buf;
va_end(ap);
}
/*
* Return a dynamically-allocated copy of the current error message, if any.
*/
static char *
errmsg_save(void)
{
return error_message == NULL ? NULL : xstrdup(error_message);
}
/*
* Restore the current error message from a copy which was previously saved
* by errmsg_save(). The copy is freed.
*/
static void
errmsg_restore(char *saved_msg)
{
if (saved_msg == NULL)
error_message = NULL;
else {
_rtld_error("%s", saved_msg);
free(saved_msg);
}
}
static const char *
basename(const char *name)
{
const char *p = strrchr(name, '/');
return p != NULL ? p + 1 : name;
}
static void
die(void)
{
const char *msg = dlerror();
if (msg == NULL)
msg = "Fatal error";
errx(1, "%s", msg);
}
/*
* Process a shared object's DYNAMIC section, and save the important
* information in its Obj_Entry structure.
*/
static void
digest_dynamic(Obj_Entry *obj)
{
const Elf_Dyn *dynp;
Needed_Entry **needed_tail = &obj->needed;
const Elf_Dyn *dyn_rpath = NULL;
int plttype = DT_REL;
for (dynp = obj->dynamic; dynp->d_tag != DT_NULL; dynp++) {
switch (dynp->d_tag) {
case DT_REL:
obj->rel = (const Elf_Rel *) (obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_RELSZ:
obj->relsize = dynp->d_un.d_val;
break;
case DT_RELENT:
assert(dynp->d_un.d_val == sizeof(Elf_Rel));
break;
case DT_JMPREL:
obj->pltrel = (const Elf_Rel *)
(obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_PLTRELSZ:
obj->pltrelsize = dynp->d_un.d_val;
break;
case DT_RELA:
obj->rela = (const Elf_Rela *) (obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_RELASZ:
obj->relasize = dynp->d_un.d_val;
break;
case DT_RELAENT:
assert(dynp->d_un.d_val == sizeof(Elf_Rela));
break;
case DT_PLTREL:
plttype = dynp->d_un.d_val;
assert(dynp->d_un.d_val == DT_REL || plttype == DT_RELA);
break;
case DT_SYMTAB:
obj->symtab = (const Elf_Sym *)
(obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_SYMENT:
assert(dynp->d_un.d_val == sizeof(Elf_Sym));
break;
case DT_STRTAB:
obj->strtab = (const char *) (obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_STRSZ:
obj->strsize = dynp->d_un.d_val;
break;
case DT_HASH:
{
const Elf_Addr *hashtab = (const Elf_Addr *)
(obj->relocbase + dynp->d_un.d_ptr);
obj->nbuckets = hashtab[0];
obj->nchains = hashtab[1];
obj->buckets = hashtab + 2;
obj->chains = obj->buckets + obj->nbuckets;
}
break;
case DT_NEEDED:
if (!obj->rtld) {
Needed_Entry *nep = NEW(Needed_Entry);
nep->name = dynp->d_un.d_val;
nep->obj = NULL;
nep->next = NULL;
*needed_tail = nep;
needed_tail = &nep->next;
}
break;
case DT_PLTGOT:
obj->pltgot = (Elf_Addr *) (obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_TEXTREL:
obj->textrel = true;
break;
case DT_SYMBOLIC:
obj->symbolic = true;
break;
case DT_RPATH:
/*
* We have to wait until later to process this, because we
* might not have gotten the address of the string table yet.
*/
dyn_rpath = dynp;
break;
case DT_SONAME:
/* Not used by the dynamic linker. */
break;
case DT_INIT:
obj->init = (InitFunc) (obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_FINI:
obj->fini = (InitFunc) (obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_DEBUG:
/* XXX - not implemented yet */
dbg("Filling in DT_DEBUG entry");
((Elf_Dyn*)dynp)->d_un.d_ptr = (Elf_Addr) &r_debug;
break;
default:
dbg("Ignoring d_tag %d = %#x", dynp->d_tag, dynp->d_tag);
break;
}
}
obj->traced = false;
if (plttype == DT_RELA) {
obj->pltrela = (const Elf_Rela *) obj->pltrel;
obj->pltrel = NULL;
obj->pltrelasize = obj->pltrelsize;
obj->pltrelsize = 0;
}
if (dyn_rpath != NULL)
obj->rpath = obj->strtab + dyn_rpath->d_un.d_val;
}
/*
* Process a shared object's program header. This is used only for the
* main program, when the kernel has already loaded the main program
* into memory before calling the dynamic linker. It creates and
* returns an Obj_Entry structure.
*/
static Obj_Entry *
digest_phdr(const Elf_Phdr *phdr, int phnum, caddr_t entry, const char *path)
{
Obj_Entry *obj;
const Elf_Phdr *phlimit = phdr + phnum;
const Elf_Phdr *ph;
int nsegs = 0;
obj = obj_new();
for (ph = phdr; ph < phlimit; ph++) {
switch (ph->p_type) {
case PT_PHDR:
if ((const Elf_Phdr *)ph->p_vaddr != phdr) {
_rtld_error("%s: invalid PT_PHDR", path);
return NULL;
}
obj->phdr = (const Elf_Phdr *) ph->p_vaddr;
obj->phsize = ph->p_memsz;
break;
case PT_INTERP:
obj->interp = (const char *) ph->p_vaddr;
break;
case PT_LOAD:
if (nsegs >= 2) {
_rtld_error("%s: too many PT_LOAD segments", path);
return NULL;
}
if (nsegs == 0) { /* First load segment */
obj->vaddrbase = trunc_page(ph->p_vaddr);
obj->mapbase = (caddr_t) obj->vaddrbase;
obj->relocbase = obj->mapbase - obj->vaddrbase;
obj->textsize = round_page(ph->p_vaddr + ph->p_memsz) -
obj->vaddrbase;
} else { /* Last load segment */
obj->mapsize = round_page(ph->p_vaddr + ph->p_memsz) -
obj->vaddrbase;
}
nsegs++;
break;
case PT_DYNAMIC:
obj->dynamic = (const Elf_Dyn *) ph->p_vaddr;
break;
}
}
if (nsegs < 2) {
_rtld_error("%s: too few PT_LOAD segments", path);
return NULL;
}
obj->entry = entry;
return obj;
}
static Obj_Entry *
dlcheck(void *handle)
{
Obj_Entry *obj;
for (obj = obj_list; obj != NULL; obj = obj->next)
if (obj == (Obj_Entry *) handle)
break;
if (obj == NULL || obj->refcount == 0 || obj->dl_refcount == 0) {
_rtld_error("Invalid shared object handle %p", handle);
return NULL;
}
return obj;
}
/*
* If the given object is already in the donelist, return true. Otherwise
* add the object to the list and return false.
*/
static bool
donelist_check(DoneList *dlp, const Obj_Entry *obj)
{
unsigned int i;
for (i = 0; i < dlp->num_used; i++)
if (dlp->objs[i] == obj)
return true;
/*
* Our donelist allocation should always be sufficient. But if
* our threads locking isn't working properly, more shared objects
* could have been loaded since we allocated the list. That should
* never happen, but we'll handle it properly just in case it does.
*/
if (dlp->num_used < dlp->num_alloc)
dlp->objs[dlp->num_used++] = obj;
return false;
}
/*
* Hash function for symbol table lookup. Don't even think about changing
* this. It is specified by the System V ABI.
*/
unsigned long
elf_hash(const char *name)
{
const unsigned char *p = (const unsigned char *) name;
unsigned long h = 0;
unsigned long g;
while (*p != '\0') {
h = (h << 4) + *p++;
if ((g = h & 0xf0000000) != 0)
h ^= g >> 24;
h &= ~g;
}
return h;
}
/*
* Find the library with the given name, and return its full pathname.
* The returned string is dynamically allocated. Generates an error
* message and returns NULL if the library cannot be found.
*
* If the second argument is non-NULL, then it refers to an already-
* loaded shared object, whose library search path will be searched.
*
* The search order is:
* rpath in the referencing file
* LD_LIBRARY_PATH
* ldconfig hints
* /usr/lib
*/
static char *
find_library(const char *name, const Obj_Entry *refobj)
{
char *pathname;
if (strchr(name, '/') != NULL) { /* Hard coded pathname */
if (name[0] != '/' && !trust) {
_rtld_error("Absolute pathname required for shared object \"%s\"",
name);
return NULL;
}
return xstrdup(name);
}
dbg(" Searching for \"%s\"", name);
if ((refobj != NULL &&
(pathname = search_library_path(name, refobj->rpath)) != NULL) ||
(pathname = search_library_path(name, ld_library_path)) != NULL ||
(pathname = search_library_path(name, gethints())) != NULL ||
(pathname = search_library_path(name, STANDARD_LIBRARY_PATH)) != NULL)
return pathname;
_rtld_error("Shared object \"%s\" not found", name);
return NULL;
}
/*
* Given a symbol number in a referencing object, find the corresponding
* definition of the symbol. Returns a pointer to the symbol, or NULL if
* no definition was found. Returns a pointer to the Obj_Entry of the
* defining object via the reference parameter DEFOBJ_OUT.
*/
const Elf_Sym *
find_symdef(unsigned long symnum, const Obj_Entry *refobj,
const Obj_Entry **defobj_out, bool in_plt, SymCache *cache)
{
const Elf_Sym *ref;
const Elf_Sym *def;
const Obj_Entry *defobj;
const char *name;
unsigned long hash;
/*
* If we have already found this symbol, get the information from
* the cache.
*/
if (symnum >= refobj->nchains)
return NULL; /* Bad object */
if (cache != NULL && cache[symnum].sym != NULL) {
*defobj_out = cache[symnum].obj;
return cache[symnum].sym;
}
ref = refobj->symtab + symnum;
name = refobj->strtab + ref->st_name;
hash = elf_hash(name);
defobj = NULL;
def = symlook_default(name, hash, refobj, &defobj, in_plt);
/*
* If we found no definition and the reference is weak, treat the
* symbol as having the value zero.
*/
if (def == NULL && ELF_ST_BIND(ref->st_info) == STB_WEAK) {
def = &sym_zero;
defobj = obj_main;
}
if (def != NULL) {
*defobj_out = defobj;
/* Record the information in the cache to avoid subsequent lookups. */
if (cache != NULL) {
cache[symnum].sym = def;
cache[symnum].obj = defobj;
}
} else
_rtld_error("%s: Undefined symbol \"%s\"", refobj->path, name);
return def;
}
/*
* Return the search path from the ldconfig hints file, reading it if
* necessary. Returns NULL if there are problems with the hints file,
* or if the search path there is empty.
*/
static const char *
gethints(void)
{
static char *hints;
if (hints == NULL) {
int fd;
struct elfhints_hdr hdr;
char *p;
/* Keep from trying again in case the hints file is bad. */
hints = "";
if ((fd = open(_PATH_ELF_HINTS, O_RDONLY)) == -1)
return NULL;
if (read(fd, &hdr, sizeof hdr) != sizeof hdr ||
hdr.magic != ELFHINTS_MAGIC ||
hdr.version != 1) {
close(fd);
return NULL;
}
p = xmalloc(hdr.dirlistlen + 1);
if (lseek(fd, hdr.strtab + hdr.dirlist, SEEK_SET) == -1 ||
read(fd, p, hdr.dirlistlen + 1) != hdr.dirlistlen + 1) {
free(p);
close(fd);
return NULL;
}
hints = p;
close(fd);
}
return hints[0] != '\0' ? hints : NULL;
}
static void
init_dag(Obj_Entry *root)
{
DoneList donelist;
donelist_init(&donelist);
init_dag1(root, root, &donelist);
}
static void
init_dag1(Obj_Entry *root, Obj_Entry *obj, DoneList *dlp)
{
const Needed_Entry *needed;
if (donelist_check(dlp, obj))
return;
objlist_push_tail(&obj->dldags, root);
objlist_push_tail(&root->dagmembers, obj);
for (needed = obj->needed; needed != NULL; needed = needed->next)
if (needed->obj != NULL)
init_dag1(root, needed->obj, dlp);
}
/*
* 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 relocate the dynamic linker.
*/
static void
init_rtld(caddr_t mapbase)
{
/*
* Conjure up an Obj_Entry structure for the dynamic linker.
*
* The "path" member is supposed to be dynamically-allocated, but we
* aren't yet initialized sufficiently to do that. Below we will
* replace the static version with a dynamically-allocated copy.
*/
obj_rtld.path = PATH_RTLD;
obj_rtld.rtld = true;
obj_rtld.mapbase = mapbase;
#ifdef PIC
obj_rtld.relocbase = mapbase;
#endif
if (&_DYNAMIC != 0) {
obj_rtld.dynamic = rtld_dynamic(&obj_rtld);
digest_dynamic(&obj_rtld);
assert(obj_rtld.needed == NULL);
assert(!obj_rtld.textrel);
/*
* Temporarily put the dynamic linker entry into the object list, so
* that symbols can be found.
*/
obj_list = &obj_rtld;
obj_tail = &obj_rtld.next;
obj_count = 1;
relocate_objects(&obj_rtld, true);
}
/* Make the object list empty again. */
obj_list = NULL;
obj_tail = &obj_list;
obj_count = 0;
/* Replace the path with a dynamically allocated copy. */
obj_rtld.path = xstrdup(obj_rtld.path);
r_debug.r_brk = r_debug_state;
r_debug.r_state = RT_CONSISTENT;
}
/*
* Add the init functions from a needed object list (and its recursive
* needed objects) to "list". This is not used directly; it is a helper
* function for initlist_add_objects(). The write lock must be held
* when this function is called.
*/
static void
initlist_add_neededs(Needed_Entry *needed, Objlist *list)
{
/* Recursively process the successor needed objects. */
if (needed->next != NULL)
initlist_add_neededs(needed->next, list);
/* Process the current needed object. */
if (needed->obj != NULL)
initlist_add_objects(needed->obj, &needed->obj->next, list);
}
/*
* Scan all of the DAGs rooted in the range of objects from "obj" to
* "tail" and add their init functions to "list". This recurses over
* the DAGs and ensure the proper init ordering such that each object's
* needed libraries are initialized before the object itself. At the
* same time, this function adds the objects to the global finalization
* list "list_fini" in the opposite order. The write lock must be
* held when this function is called.
*/
static void
initlist_add_objects(Obj_Entry *obj, Obj_Entry **tail, Objlist *list)
{
if (obj->init_done)
return;
obj->init_done = true;
/* Recursively process the successor objects. */
if (&obj->next != tail)
initlist_add_objects(obj->next, tail, list);
/* Recursively process the needed objects. */
if (obj->needed != NULL)
initlist_add_neededs(obj->needed, list);
/* Add the object to the init list. */
if (obj->init != NULL)
objlist_push_tail(list, obj);
/* Add the object to the global fini list in the reverse order. */
if (obj->fini != NULL)
objlist_push_head(&list_fini, obj);
}
static bool
is_exported(const Elf_Sym *def)
{
func_ptr_type value;
const func_ptr_type *p;
value = (func_ptr_type)(obj_rtld.relocbase + def->st_value);
for (p = exports; *p != NULL; p++)
if (*p == value)
return true;
return false;
}
/*
* Given a shared object, traverse its list of needed objects, and load
* each of them. Returns 0 on success. Generates an error message and
* returns -1 on failure.
*/
static int
load_needed_objects(Obj_Entry *first)
{
Obj_Entry *obj;
for (obj = first; obj != NULL; obj = obj->next) {
Needed_Entry *needed;
for (needed = obj->needed; needed != NULL; needed = needed->next) {
const char *name = obj->strtab + needed->name;
char *path = find_library(name, obj);
needed->obj = NULL;
if (path == NULL && !ld_tracing)
return -1;
if (path) {
needed->obj = load_object(path);
if (needed->obj == NULL && !ld_tracing)
return -1; /* XXX - cleanup */
}
}
}
return 0;
}
static int
load_preload_objects(void)
{
char *p = ld_preload;
static const char delim[] = " \t:;";
if (p == NULL)
return NULL;
p += strspn(p, delim);
while (*p != '\0') {
size_t len = strcspn(p, delim);
char *path;
char savech;
savech = p[len];
p[len] = '\0';
if ((path = find_library(p, NULL)) == NULL)
return -1;
if (load_object(path) == NULL)
return -1; /* XXX - cleanup */
p[len] = savech;
p += len;
p += strspn(p, delim);
}
return 0;
}
/*
* Load a shared object into memory, if it is not already loaded. The
* argument must be a string allocated on the heap. This function assumes
* responsibility for freeing it when necessary.
*
* Returns a pointer to the Obj_Entry for the object. Returns NULL
* on failure.
*/
static Obj_Entry *
load_object(char *path)
{
Obj_Entry *obj;
int fd = -1;
struct stat sb;
for (obj = obj_list->next; obj != NULL; obj = obj->next)
if (strcmp(obj->path, path) == 0)
break;
/*
* If we didn't find a match by pathname, open the file and check
* again by device and inode. This avoids false mismatches caused
* by multiple links or ".." in pathnames.
*
* To avoid a race, we open the file and use fstat() rather than
* using stat().
*/
if (obj == NULL) {
if ((fd = open(path, O_RDONLY)) == -1) {
_rtld_error("Cannot open \"%s\"", path);
return NULL;
}
if (fstat(fd, &sb) == -1) {
_rtld_error("Cannot fstat \"%s\"", path);
close(fd);
return NULL;
}
for (obj = obj_list->next; obj != NULL; obj = obj->next) {
if (obj->ino == sb.st_ino && obj->dev == sb.st_dev) {
close(fd);
break;
}
}
}
if (obj == NULL) { /* First use of this object, so we must map it in */
dbg("loading \"%s\"", path);
obj = map_object(fd, path, &sb);
close(fd);
if (obj == NULL) {
free(path);
return NULL;
}
obj->path = path;
digest_dynamic(obj);
*obj_tail = obj;
obj_tail = &obj->next;
obj_count++;
linkmap_add(obj); /* for GDB */
dbg(" %p .. %p: %s", obj->mapbase,
obj->mapbase + obj->mapsize - 1, obj->path);
if (obj->textrel)
dbg(" WARNING: %s has impure text", obj->path);
} else
free(path);
obj->refcount++;
return obj;
}
/*
* Check for locking violations and die if one is found.
*/
static void
lock_check(void)
{
int rcount, wcount;
rcount = lockinfo.rcount;
wcount = lockinfo.wcount;
assert(rcount >= 0);
assert(wcount >= 0);
if (wcount > 1 || (wcount != 0 && rcount != 0)) {
_rtld_error("Application locking error: %d readers and %d writers"
" in dynamic linker. See DLLOCKINIT(3) in manual pages.",
rcount, wcount);
die();
}
}
static Obj_Entry *
obj_from_addr(const void *addr)
{
unsigned long endhash;
Obj_Entry *obj;
endhash = elf_hash(END_SYM);
for (obj = obj_list; obj != NULL; obj = obj->next) {
const Elf_Sym *endsym;
if (addr < (void *) obj->mapbase)
continue;
if ((endsym = symlook_obj(END_SYM, endhash, obj, true)) == NULL)
continue; /* No "end" symbol?! */
if (addr < (void *) (obj->relocbase + endsym->st_value))
return obj;
}
return NULL;
}
/*
* Call the finalization functions for each of the objects in "list"
* which are unreferenced. All of the objects are expected to have
* non-NULL fini functions.
*/
static void
objlist_call_fini(Objlist *list)
{
Objlist_Entry *elm;
char *saved_msg;
/*
* Preserve the current error message since a fini function might
* call into the dynamic linker and overwrite it.
*/
saved_msg = errmsg_save();
STAILQ_FOREACH(elm, list, link) {
if (elm->obj->refcount == 0) {
dbg("calling fini function for %s", elm->obj->path);
(*elm->obj->fini)();
}
}
errmsg_restore(saved_msg);
}
/*
* Call the initialization functions for each of the objects in
* "list". All of the objects are expected to have non-NULL init
* functions.
*/
static void
objlist_call_init(Objlist *list)
{
Objlist_Entry *elm;
char *saved_msg;
/*
* Preserve the current error message since an init function might
* call into the dynamic linker and overwrite it.
*/
saved_msg = errmsg_save();
STAILQ_FOREACH(elm, list, link) {
dbg("calling init function for %s", elm->obj->path);
(*elm->obj->init)();
}
errmsg_restore(saved_msg);
}
static void
objlist_clear(Objlist *list)
{
Objlist_Entry *elm;
while (!STAILQ_EMPTY(list)) {
elm = STAILQ_FIRST(list);
STAILQ_REMOVE_HEAD(list, link);
free(elm);
}
}
static Objlist_Entry *
objlist_find(Objlist *list, const Obj_Entry *obj)
{
Objlist_Entry *elm;
STAILQ_FOREACH(elm, list, link)
if (elm->obj == obj)
return elm;
return NULL;
}
static void
objlist_init(Objlist *list)
{
STAILQ_INIT(list);
}
static void
objlist_push_head(Objlist *list, Obj_Entry *obj)
{
Objlist_Entry *elm;
elm = NEW(Objlist_Entry);
elm->obj = obj;
STAILQ_INSERT_HEAD(list, elm, link);
}
static void
objlist_push_tail(Objlist *list, Obj_Entry *obj)
{
Objlist_Entry *elm;
elm = NEW(Objlist_Entry);
elm->obj = obj;
STAILQ_INSERT_TAIL(list, elm, link);
}
static void
objlist_remove(Objlist *list, Obj_Entry *obj)
{
Objlist_Entry *elm;
if ((elm = objlist_find(list, obj)) != NULL) {
STAILQ_REMOVE(list, elm, Struct_Objlist_Entry, link);
free(elm);
}
}
/*
* Remove all of the unreferenced objects from "list".
*/
static void
objlist_remove_unref(Objlist *list)
{
Objlist newlist;
Objlist_Entry *elm;
STAILQ_INIT(&newlist);
while (!STAILQ_EMPTY(list)) {
elm = STAILQ_FIRST(list);
STAILQ_REMOVE_HEAD(list, link);
if (elm->obj->refcount == 0)
free(elm);
else
STAILQ_INSERT_TAIL(&newlist, elm, link);
}
*list = newlist;
}
/*
* Relocate newly-loaded shared objects. The argument is a pointer to
* the Obj_Entry for the first such object. All objects from the first
* to the end of the list of objects are relocated. Returns 0 on success,
* or -1 on failure.
*/
static int
relocate_objects(Obj_Entry *first, bool bind_now)
{
Obj_Entry *obj;
for (obj = first; obj != NULL; obj = obj->next) {
if (obj != &obj_rtld)
dbg("relocating \"%s\"", obj->path);
if (obj->nbuckets == 0 || obj->nchains == 0 || obj->buckets == NULL ||
obj->symtab == NULL || obj->strtab == NULL) {
_rtld_error("%s: Shared object has no run-time symbol table",
obj->path);
return -1;
}
if (obj->textrel) {
/* There are relocations to the write-protected text segment. */
if (mprotect(obj->mapbase, obj->textsize,
PROT_READ|PROT_WRITE|PROT_EXEC) == -1) {
_rtld_error("%s: Cannot write-enable text segment: %s",
obj->path, strerror(errno));
return -1;
}
}
/* Process the non-PLT relocations. */
if (reloc_non_plt(obj, &obj_rtld))
return -1;
if (obj->textrel) { /* Re-protected the text segment. */
if (mprotect(obj->mapbase, obj->textsize,
PROT_READ|PROT_EXEC) == -1) {
_rtld_error("%s: Cannot write-protect text segment: %s",
obj->path, strerror(errno));
return -1;
}
}
/* Process the PLT relocations. */
if (reloc_plt(obj) == -1)
return -1;
/* Relocate the jump slots if we are doing immediate binding. */
if (bind_now)
if (reloc_jmpslots(obj) == -1)
return -1;
/*
* Set up the magic number and version in the Obj_Entry. These
* were checked in the crt1.o from the original ElfKit, so we
* set them for backward compatibility.
*/
obj->magic = RTLD_MAGIC;
obj->version = RTLD_VERSION;
/* Set the special PLT or GOT entries. */
init_pltgot(obj);
}
return 0;
}
/*
* Cleanup procedure. It will be called (by the atexit mechanism) just
* before the process exits.
*/
static void
rtld_exit(void)
{
Obj_Entry *obj;
dbg("rtld_exit()");
wlock_acquire();
/* Clear all the reference counts so the fini functions will be called. */
for (obj = obj_list; obj != NULL; obj = obj->next)
obj->refcount = 0;
wlock_release();
objlist_call_fini(&list_fini);
/* No need to remove the items from the list, since we are exiting. */
}
static char *
search_library_path(const char *name, const char *path)
{
size_t namelen = strlen(name);
const char *p = path;
if (p == NULL)
return NULL;
p += strspn(p, ":;");
while (*p != '\0') {
size_t len = strcspn(p, ":;");
if (*p == '/' || trust) {
char *pathname;
const char *dir = p;
size_t dirlen = len;
pathname = xmalloc(dirlen + 1 + namelen + 1);
strncpy(pathname, dir, dirlen);
pathname[dirlen] = '/';
strcpy(pathname + dirlen + 1, name);
dbg(" Trying \"%s\"", pathname);
if (access(pathname, F_OK) == 0) /* We found it */
return pathname;
free(pathname);
}
p += len;
p += strspn(p, ":;");
}
return NULL;
}
int
dlclose(void *handle)
{
Obj_Entry *root;
wlock_acquire();
root = dlcheck(handle);
if (root == NULL) {
wlock_release();
return -1;
}
/* Unreference the object and its dependencies. */
root->dl_refcount--;
unref_dag(root);
if (root->refcount == 0) {
/*
* The object is no longer referenced, so we must unload it.
* First, call the fini functions with no locks held.
*/
wlock_release();
objlist_call_fini(&list_fini);
wlock_acquire();
objlist_remove_unref(&list_fini);
/* Finish cleaning up the newly-unreferenced objects. */
GDB_STATE(RT_DELETE,&root->linkmap);
unload_object(root);
GDB_STATE(RT_CONSISTENT,NULL);
}
wlock_release();
return 0;
}
const char *
dlerror(void)
{
char *msg = error_message;
error_message = NULL;
return msg;
}
/*
* This function is deprecated and has no effect.
*/
void
dllockinit(void *context,
void *(*lock_create)(void *context),
void (*rlock_acquire)(void *lock),
void (*wlock_acquire)(void *lock),
void (*lock_release)(void *lock),
void (*lock_destroy)(void *lock),
void (*context_destroy)(void *context))
{
static void *cur_context;
static void (*cur_context_destroy)(void *);
/* Just destroy the context from the previous call, if necessary. */
if (cur_context_destroy != NULL)
cur_context_destroy(cur_context);
cur_context = context;
cur_context_destroy = context_destroy;
}
void *
dlopen(const char *name, int mode)
{
Obj_Entry **old_obj_tail;
Obj_Entry *obj;
Objlist initlist;
objlist_init(&initlist);
wlock_acquire();
GDB_STATE(RT_ADD,NULL);
old_obj_tail = obj_tail;
obj = NULL;
if (name == NULL) {
obj = obj_main;
obj->refcount++;
} else {
char *path = find_library(name, obj_main);
if (path != NULL)
obj = load_object(path);
}
if (obj) {
obj->dl_refcount++;
if (mode & RTLD_GLOBAL && objlist_find(&list_global, obj) == NULL)
objlist_push_tail(&list_global, obj);
mode &= RTLD_MODEMASK;
if (*old_obj_tail != NULL) { /* We loaded something new. */
assert(*old_obj_tail == obj);
if (load_needed_objects(obj) == -1 ||
(init_dag(obj), relocate_objects(obj, mode == RTLD_NOW)) == -1) {
obj->dl_refcount--;
unref_dag(obj);
if (obj->refcount == 0)
unload_object(obj);
obj = NULL;
} else {
/* Make list of init functions to call. */
initlist_add_objects(obj, &obj->next, &initlist);
}
}
}
GDB_STATE(RT_CONSISTENT,obj ? &obj->linkmap : NULL);
/* Call the init functions with no locks held. */
wlock_release();
objlist_call_init(&initlist);
wlock_acquire();
objlist_clear(&initlist);
wlock_release();
return obj;
}
void *
dlsym(void *handle, const char *name)
{
const Obj_Entry *obj;
unsigned long hash;
const Elf_Sym *def;
const Obj_Entry *defobj;
hash = elf_hash(name);
def = NULL;
defobj = NULL;
rlock_acquire();
if (handle == NULL || handle == RTLD_NEXT || handle == RTLD_DEFAULT) {
void *retaddr;
retaddr = __builtin_return_address(0); /* __GNUC__ only */
if ((obj = obj_from_addr(retaddr)) == NULL) {
_rtld_error("Cannot determine caller's shared object");
rlock_release();
return NULL;
}
if (handle == NULL) { /* Just the caller's shared object. */
def = symlook_obj(name, hash, obj, true);
defobj = obj;
} else if (handle == RTLD_NEXT) { /* Objects after caller's */
while ((obj = obj->next) != NULL) {
if ((def = symlook_obj(name, hash, obj, true)) != NULL) {
defobj = obj;
break;
}
}
} else {
assert(handle == RTLD_DEFAULT);
def = symlook_default(name, hash, obj, &defobj, true);
}
} else {
if ((obj = dlcheck(handle)) == NULL) {
rlock_release();
return NULL;
}
if (obj->mainprog) {
DoneList donelist;
/* Search main program and all libraries loaded by it. */
donelist_init(&donelist);
def = symlook_list(name, hash, &list_main, &defobj, true,
&donelist);
} else {
/*
* XXX - This isn't correct. The search should include the whole
* DAG rooted at the given object.
*/
def = symlook_obj(name, hash, obj, true);
defobj = obj;
}
}
if (def != NULL) {
rlock_release();
return defobj->relocbase + def->st_value;
}
_rtld_error("Undefined symbol \"%s\"", name);
rlock_release();
return NULL;
}
int
dladdr(const void *addr, Dl_info *info)
{
const Obj_Entry *obj;
const Elf_Sym *def;
void *symbol_addr;
unsigned long symoffset;
rlock_acquire();
obj = obj_from_addr(addr);
if (obj == NULL) {
_rtld_error("No shared object contains address");
rlock_release();
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.
*/
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;
/* Exact match? */
if (info->dli_saddr == addr)
break;
}
rlock_release();
return 1;
}
static void
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->mapbase;
obj->linkmap.l_ld = obj->dynamic;
#ifdef __mips__
/* GDB needs load offset on MIPS to use the symbols */
obj->linkmap.l_offs = obj->relocbase;
#endif
if (r_debug.r_map == NULL) {
r_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 = r_debug.r_map;
prev->l_next != NULL && prev->l_next != &obj_rtld.linkmap;
prev = prev->l_next)
;
/* Link in the new entry. */
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;
}
static void
linkmap_delete(Obj_Entry *obj)
{
struct link_map *l = &obj->linkmap;
if (l->l_prev == NULL) {
if ((r_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;
}
/*
* Function for the debugger to set a breakpoint on to gain control.
*
* The two parameters allow the debugger to easily find and determine
* what the runtime loader is doing and to whom it is doing it.
*
* When the loadhook trap is hit (r_debug_state, set at program
* initialization), the arguments can be found on the stack:
*
* +8 struct link_map *m
* +4 struct r_debug *rd
* +0 RetAddr
*/
void
r_debug_state(struct r_debug* rd, struct link_map *m)
{
}
/*
* Set a pointer variable in the main program to the given value. This
* is used to set key variables such as "environ" before any of the
* init functions are called.
*/
static void
set_program_var(const char *name, const void *value)
{
const Obj_Entry *obj;
unsigned long hash;
hash = elf_hash(name);
for (obj = obj_main; obj != NULL; obj = obj->next) {
const Elf_Sym *def;
if ((def = symlook_obj(name, hash, obj, false)) != NULL) {
const void **addr;
addr = (const void **)(obj->relocbase + def->st_value);
dbg("\"%s\": *%p <-- %p", name, addr, value);
*addr = value;
break;
}
}
}
/*
* Given a symbol name in a referencing object, find the corresponding
* definition of the symbol. Returns a pointer to the symbol, or NULL if
* no definition was found. Returns a pointer to the Obj_Entry of the
* defining object via the reference parameter DEFOBJ_OUT.
*/
static const Elf_Sym *
symlook_default(const char *name, unsigned long hash,
const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt)
{
DoneList donelist;
const Elf_Sym *def;
const Elf_Sym *symp;
const Obj_Entry *obj;
const Obj_Entry *defobj;
const Objlist_Entry *elm;
def = NULL;
defobj = NULL;
donelist_init(&donelist);
/* Look first in the referencing object if linked symbolically. */
if (refobj->symbolic && !donelist_check(&donelist, refobj)) {
symp = symlook_obj(name, hash, refobj, in_plt);
if (symp != NULL) {
def = symp;
defobj = refobj;
}
}
/* Search all objects loaded at program start up. */
if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
symp = symlook_list(name, hash, &list_main, &obj, in_plt, &donelist);
if (symp != NULL &&
(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
def = symp;
defobj = obj;
}
}
/* Search all dlopened DAGs containing the referencing object. */
STAILQ_FOREACH(elm, &refobj->dldags, link) {
if (def != NULL && ELF_ST_BIND(def->st_info) != STB_WEAK)
break;
symp = symlook_list(name, hash, &elm->obj->dagmembers, &obj, in_plt,
&donelist);
if (symp != NULL &&
(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
def = symp;
defobj = obj;
}
}
/* Search all RTLD_GLOBAL objects. */
if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
symp = symlook_list(name, hash, &list_global, &obj, in_plt, &donelist);
if (symp != NULL &&
(def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK)) {
def = symp;
defobj = obj;
}
}
/*
* Search the dynamic linker itself, and possibly resolve the
* symbol from there. This is how the application links to
* dynamic linker services such as dlopen. Only the values listed
* in the "exports" array can be resolved from the dynamic linker.
*/
if (def == NULL || ELF_ST_BIND(def->st_info) == STB_WEAK) {
symp = symlook_obj(name, hash, &obj_rtld, in_plt);
if (symp != NULL && is_exported(symp)) {
def = symp;
defobj = &obj_rtld;
}
}
if (def != NULL)
*defobj_out = defobj;
return def;
}
static const Elf_Sym *
symlook_list(const char *name, unsigned long hash, Objlist *objlist,
const Obj_Entry **defobj_out, bool in_plt, DoneList *dlp)
{
const Elf_Sym *symp;
const Elf_Sym *def;
const Obj_Entry *defobj;
const Objlist_Entry *elm;
def = NULL;
defobj = NULL;
STAILQ_FOREACH(elm, objlist, link) {
if (donelist_check(dlp, elm->obj))
continue;
if ((symp = symlook_obj(name, hash, elm->obj, in_plt)) != NULL) {
if (def == NULL || ELF_ST_BIND(symp->st_info) != STB_WEAK) {
def = symp;
defobj = elm->obj;
if (ELF_ST_BIND(def->st_info) != STB_WEAK)
break;
}
}
}
if (def != NULL)
*defobj_out = defobj;
return def;
}
/*
* Search the symbol table of a single shared object for a symbol of
* the given name. Returns a pointer to the symbol, or NULL if no
* definition was found.
*
* The symbol's hash value is passed in for efficiency reasons; that
* eliminates many recomputations of the hash value.
*/
const Elf_Sym *
symlook_obj(const char *name, unsigned long hash, const Obj_Entry *obj,
bool in_plt)
{
if (obj->buckets != NULL) {
unsigned long symnum = obj->buckets[hash % obj->nbuckets];
while (symnum != STN_UNDEF) {
const Elf_Sym *symp;
const char *strp;
if (symnum >= obj->nchains)
return NULL; /* Bad object */
symp = obj->symtab + symnum;
strp = obj->strtab + symp->st_name;
if (name[0] == strp[0] && strcmp(name, strp) == 0)
return symp->st_shndx != SHN_UNDEF ||
(!in_plt && symp->st_value != 0 &&
ELF_ST_TYPE(symp->st_info) == STT_FUNC) ? symp : NULL;
symnum = obj->chains[symnum];
}
}
return NULL;
}
static void
trace_loaded_objects(Obj_Entry *obj)
{
char *fmt1, *fmt2, *fmt, *main_local;
int c;
if ((main_local = getenv("LD_TRACE_LOADED_OBJECTS_PROGNAME")) == NULL)
main_local = "";
if ((fmt1 = getenv("LD_TRACE_LOADED_OBJECTS_FMT1")) == NULL)
fmt1 = "\t%o => %p (%x)\n";
if ((fmt2 = getenv("LD_TRACE_LOADED_OBJECTS_FMT2")) == NULL)
fmt2 = "\t%o (%x)\n";
for (; obj; obj = obj->next) {
Needed_Entry *needed;
char *name, *path;
bool is_lib;
for (needed = obj->needed; needed; needed = needed->next) {
if (needed->obj != NULL) {
if (needed->obj->traced)
continue;
needed->obj->traced = true;
path = needed->obj->path;
} else
path = "not found";
name = (char *)obj->strtab + needed->name;
is_lib = strncmp(name, "lib", 3) == 0; /* XXX - bogus */
fmt = is_lib ? fmt1 : fmt2;
while ((c = *fmt++) != '\0') {
switch (c) {
default:
putchar(c);
continue;
case '\\':
switch (c = *fmt) {
case '\0':
continue;
case 'n':
putchar('\n');
break;
case 't':
putchar('\t');
break;
}
break;
case '%':
switch (c = *fmt) {
case '\0':
continue;
case '%':
default:
putchar(c);
break;
case 'A':
printf("%s", main_local);
break;
case 'a':
printf("%s", obj_main->path);
break;
case 'o':
printf("%s", name);
break;
#if 0
case 'm':
printf("%d", sodp->sod_major);
break;
case 'n':
printf("%d", sodp->sod_minor);
break;
#endif
case 'p':
printf("%s", path);
break;
case 'x':
printf("%p", needed->obj ? needed->obj->mapbase : 0);
break;
}
break;
}
++fmt;
}
}
}
}
/*
* Unload a dlopened object and its dependencies from memory and from
* our data structures. It is assumed that the DAG rooted in the
* object has already been unreferenced, and that the object has a
* reference count of 0.
*/
static void
unload_object(Obj_Entry *root)
{
Obj_Entry *obj;
Obj_Entry **linkp;
Objlist_Entry *elm;
assert(root->refcount == 0);
/* Remove the DAG from all objects' DAG lists. */
STAILQ_FOREACH(elm, &root->dagmembers , link)
objlist_remove(&elm->obj->dldags, root);
/* Remove the DAG from the RTLD_GLOBAL list. */
objlist_remove(&list_global, root);
/* Unmap all objects that are no longer referenced. */
linkp = &obj_list->next;
while ((obj = *linkp) != NULL) {
if (obj->refcount == 0) {
dbg("unloading \"%s\"", obj->path);
munmap(obj->mapbase, obj->mapsize);
linkmap_delete(obj);
*linkp = obj->next;
obj_count--;
obj_free(obj);
} else
linkp = &obj->next;
}
obj_tail = linkp;
}
static void
unref_dag(Obj_Entry *root)
{
const Needed_Entry *needed;
if (root->refcount == 0)
return;
root->refcount--;
if (root->refcount == 0)
for (needed = root->needed; needed != NULL; needed = needed->next)
if (needed->obj != NULL)
unref_dag(needed->obj);
}
/*
* Non-mallocing printf, for use by malloc itself.
* XXX - This doesn't belong in this module.
*/
void
xprintf(const char *fmt, ...)
{
char buf[256];
va_list ap;
va_start(ap, fmt);
vsprintf(buf, fmt, ap);
(void)write(1, buf, strlen(buf));
va_end(ap);
}
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