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freebsd-dev/libexec/rtld-elf/rtld.c
John Polstra b19042b569 Make LD_PRELOAD work for ELF.
1998-09-22 02:09:56 +00:00

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/*-
* Copyright 1996-1998 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.
*
* $Id: rtld.c,v 1.10 1998/09/16 02:54:08 jdp Exp $
*/
/*
* 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 <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"
/*
* Debugging support.
*/
#define assert(cond) ((cond) ? (void) 0 :\
(msg("oops: " __XSTRING(__LINE__) "\n"), abort()))
#define msg(s) (write(1, s, strlen(s)))
#define trace() msg("trace: " __XSTRING(__LINE__) "\n");
#define END_SYM "end"
/* Types. */
typedef void (*func_ptr_type)();
/*
* Function declarations.
*/
static void call_fini_functions(Obj_Entry *);
static void call_init_functions(Obj_Entry *);
static void die(void);
static void digest_dynamic(Obj_Entry *);
static Obj_Entry *digest_phdr(const Elf_Phdr *, int, caddr_t);
static Obj_Entry *dlcheck(void *);
static char *find_library(const char *, const Obj_Entry *);
static const char *gethints(void);
static void init_rtld(caddr_t);
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 Obj_Entry *obj_from_addr(const void *);
static int relocate_objects(Obj_Entry *, bool);
static void rtld_exit(void);
static char *search_library_path(const char *, const char *);
static void unref_object_dag(Obj_Entry *);
static void trace_loaded_objects(Obj_Entry *obj);
void r_debug_state(void);
void xprintf(const char *, ...);
#ifdef DEBUG
static const char *basename(const char *);
#endif
/* Assembly language entry point for lazy binding. */
extern void _rtld_bind_start(void);
/*
* Assembly language macro for getting the GOT pointer.
*/
#ifdef __i386__
#define get_got_address() \
({ Elf_Addr *thegot; \
__asm__("movl %%ebx,%0" : "=rm"(thegot)); \
thegot; })
#elif __alpha__
#define get_got_address() NULL
#else
#error "This file only supports the i386 and alpha architectures"
#endif
/*
* 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 **main_tail; /* Value of obj_tail after loading main and
its needed shared libraries */
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 */
#define GDB_STATE(s) r_debug.r_state = s; r_debug_state();
extern Elf_Dyn _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,
NULL
};
/*
* Global declarations normally provided by crt1. The dynamic linker is
* not build with crt1, so we have to provide them ourselves.
*/
char *__progname;
char **environ;
/*
* 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;
/*
* 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;
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);
/*
* 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);
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;
obj_main = digest_phdr(phdr, phnum, entry);
}
obj_main->path = xstrdup(argv[0]);
obj_main->mainprog = true;
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_main->refcount++;
dbg("loading LD_PRELOAD libraries");
if (load_preload_objects() == -1)
die();
dbg("loading needed objects");
if (load_needed_objects(obj_main) == -1)
die();
main_tail = obj_tail;
if (ld_tracing) { /* We're done */
trace_loaded_objects(obj_main);
exit(0);
}
dbg("relocating objects");
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("calling _init functions");
call_init_functions(obj_main->next);
dbg("transferring control to program entry point = %p", obj_main->entry);
r_debug_state(); /* say hello to gdb! */
/* Return the exit procedure and the program entry point. */
*exit_proc = rtld_exit;
*objp = obj_main;
return (func_ptr_type) obj_main->entry;
}
caddr_t
_rtld_bind(const Obj_Entry *obj, Elf_Word reloff)
{
const Elf_Rel *rel;
const Elf_Sym *def;
const Obj_Entry *defobj;
Elf_Addr *where;
caddr_t target;
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);
if (def == NULL)
die();
target = (caddr_t) (defobj->relocbase + def->st_value);
dbg("\"%s\" in \"%s\" ==> %p in \"%s\"",
defobj->strtab + def->st_name, basename(obj->path),
target, basename(defobj->path));
*where = (Elf_Addr) target;
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);
}
#ifdef DEBUG
static const char *
basename(const char *name)
{
const char *p = strrchr(name, '/');
return p != NULL ? p + 1 : name;
}
#endif
static void
call_fini_functions(Obj_Entry *first)
{
Obj_Entry *obj;
for (obj = first; obj != NULL; obj = obj->next)
if (obj->fini != NULL)
(*obj->fini)();
}
static void
call_init_functions(Obj_Entry *first)
{
if (first != NULL) {
call_init_functions(first->next);
if (first->init != NULL)
(*first->init)();
}
}
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:
assert(!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->got = (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 = (void (*)(void)) (obj->relocbase + dynp->d_un.d_ptr);
break;
case DT_FINI:
obj->fini = (void (*)(void)) (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:
xprintf("Ignored d_tag %d\n",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)
{
Obj_Entry *obj = CNEW(Obj_Entry);
const Elf_Phdr *phlimit = phdr + phnum;
const Elf_Phdr *ph;
int nsegs = 0;
for (ph = phdr; ph < phlimit; ph++) {
switch (ph->p_type) {
case PT_PHDR:
assert((const Elf_Phdr *) ph->p_vaddr == phdr);
obj->phdr = (const Elf_Phdr *) ph->p_vaddr;
obj->phsize = ph->p_memsz;
break;
case PT_LOAD:
assert(nsegs < 2);
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;
}
}
assert(nsegs == 2);
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->dl_refcount == 0) {
_rtld_error("Invalid shared object handle %p", handle);
return NULL;
}
return obj;
}
/*
* 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:
* LD_LIBRARY_PATH
* ldconfig hints
* rpath in the referencing file
* /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 ((pathname = search_library_path(name, ld_library_path)) != NULL ||
(pathname = search_library_path(name, gethints())) != NULL ||
(refobj != NULL &&
(pathname = search_library_path(name, refobj->rpath)) != 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)
{
const Elf_Sym *ref;
const Elf_Sym *strongdef;
const Elf_Sym *weakdef;
const Obj_Entry *obj;
const Obj_Entry *strongobj;
const Obj_Entry *weakobj;
const char *name;
unsigned long hash;
ref = refobj->symtab + symnum;
name = refobj->strtab + ref->st_name;
hash = elf_hash(name);
if (refobj->symbolic) { /* Look first in the referencing object */
const Elf_Sym *def = symlook_obj(name, hash, refobj, in_plt);
if (def != NULL) {
*defobj_out = refobj;
return def;
}
}
/*
* Look in all loaded objects. Skip the referencing object, if
* we have already searched it. We keep track of the first weak
* definition and the first strong definition we encounter. If
* we find a strong definition we stop searching, because there
* won't be anything better than that.
*/
strongdef = weakdef = NULL;
strongobj = weakobj = NULL;
for (obj = obj_list; obj != NULL; obj = obj->next) {
if (obj != refobj || !refobj->symbolic) {
const Elf_Sym *def = symlook_obj(name, hash, obj, in_plt);
if (def != NULL) {
if (ELF_ST_BIND(def->st_info) == STB_WEAK) {
if (weakdef == NULL) {
weakdef = def;
weakobj = obj;
}
} else {
strongdef = def;
strongobj = obj;
break; /* We are done. */
}
}
}
}
/*
* If we still don't have a strong definition, 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 (strongdef == NULL) {
const Elf_Sym *def = symlook_obj(name, hash, &obj_rtld, in_plt);
if (def != NULL && is_exported(def)) {
if (ELF_ST_BIND(def->st_info) == STB_WEAK) {
if (weakdef == NULL) {
weakdef = def;
weakobj = &obj_rtld;
}
} else {
strongdef = def;
strongobj = &obj_rtld;
}
}
}
if (strongdef != NULL) {
*defobj_out = strongobj;
return strongdef;
}
if (weakdef != NULL) {
*defobj_out = weakobj;
return weakdef;
}
_rtld_error("%s: Undefined symbol \"%s\"", refobj->path, name);
return NULL;
}
/*
* 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;
}
/*
* 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 = "/usr/libexec/ld-elf.so.1";
obj_rtld.rtld = true;
obj_rtld.mapbase = mapbase;
obj_rtld.relocbase = mapbase;
obj_rtld.got = get_got_address();
#ifdef __alpha__
obj_rtld.dynamic = (const Elf_Dyn *) &_DYNAMIC;
#else
obj_rtld.dynamic = (const Elf_Dyn *) (obj_rtld.mapbase + obj_rtld.got[0]);
#endif
digest_dynamic(&obj_rtld);
#ifdef __alpha__
/* XXX XXX XXX */
obj_rtld.got = NULL;
#endif
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;
relocate_objects(&obj_rtld, true);
/* Make the object list empty again. */
obj_list = NULL;
obj_tail = &obj_list;
/* 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;
}
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;
if (p == NULL)
return NULL;
p += strspn(p, ":;");
while (*p != '\0') {
size_t len = strcspn(p, ":;");
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, ":;");
}
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;
for (obj = obj_list->next; obj != NULL; obj = obj->next)
if (strcmp(obj->path, path) == 0)
break;
if (obj == NULL) { /* First use of this object, so we must map it in */
int fd;
if ((fd = open(path, O_RDONLY)) == -1) {
_rtld_error("Cannot open \"%s\"", path);
return NULL;
}
obj = map_object(fd);
close(fd);
if (obj == NULL) {
free(path);
return NULL;
}
obj->path = path;
digest_dynamic(obj);
*obj_tail = obj;
obj_tail = &obj->next;
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;
}
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;
}
/*
* 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, bind_now))
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 GOT entries. */
if (obj->got) {
#ifdef __i386__
obj->got[1] = (Elf_Addr) obj;
obj->got[2] = (Elf_Addr) &_rtld_bind_start;
#endif
#ifdef __alpha__
/* This function will be called to perform the relocation. */
obj->got[2] = (Elf_Addr) &_rtld_bind_start;
/* Identify this shared object */
obj->got[3] = (Elf_Addr) obj;
#endif
}
}
return 0;
}
/*
* Cleanup procedure. It will be called (by the atexit mechanism) just
* before the process exits.
*/
static void
rtld_exit(void)
{
dbg("rtld_exit()");
call_fini_functions(obj_list->next);
}
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 = dlcheck(handle);
if (root == NULL)
return -1;
GDB_STATE(RT_DELETE);
root->dl_refcount--;
unref_object_dag(root);
if (root->refcount == 0) { /* We are finished with some objects. */
Obj_Entry *obj;
Obj_Entry **linkp;
/* Finalize objects that are about to be unmapped. */
for (obj = obj_list->next; obj != NULL; obj = obj->next)
if (obj->refcount == 0 && obj->fini != NULL)
(*obj->fini)();
/* Unmap all objects that are no longer referenced. */
linkp = &obj_list->next;
while ((obj = *linkp) != NULL) {
if (obj->refcount == 0) {
munmap(obj->mapbase, obj->mapsize);
free(obj->path);
while (obj->needed != NULL) {
Needed_Entry *needed = obj->needed;
obj->needed = needed->next;
free(needed);
}
linkmap_delete(obj);
*linkp = obj->next;
free(obj);
} else
linkp = &obj->next;
}
}
GDB_STATE(RT_CONSISTENT);
return 0;
}
const char *
dlerror(void)
{
char *msg = error_message;
error_message = NULL;
return msg;
}
void *
dlopen(const char *name, int mode)
{
Obj_Entry **old_obj_tail = obj_tail;
Obj_Entry *obj = NULL;
GDB_STATE(RT_ADD);
if (name == NULL)
obj = obj_main;
else {
char *path = find_library(name, NULL);
if (path != NULL)
obj = load_object(path);
}
if (obj) {
obj->dl_refcount++;
if (*old_obj_tail != NULL) { /* We loaded something new. */
assert(*old_obj_tail == obj);
/* XXX - Clean up properly after an error. */
if (load_needed_objects(obj) == -1) {
obj->dl_refcount--;
obj = NULL;
} else if (relocate_objects(obj, mode == RTLD_NOW) == -1) {
obj->dl_refcount--;
obj = NULL;
} else
call_init_functions(obj);
}
}
GDB_STATE(RT_CONSISTENT);
return obj;
}
void *
dlsym(void *handle, const char *name)
{
const Obj_Entry *obj;
unsigned long hash;
const Elf_Sym *def;
hash = elf_hash(name);
def = NULL;
if (handle == NULL || handle == RTLD_NEXT) {
void *retaddr;
retaddr = __builtin_return_address(0); /* __GNUC__ only */
if ((obj = obj_from_addr(retaddr)) == NULL) {
_rtld_error("Cannot determine caller's shared object");
return NULL;
}
if (handle == NULL) /* Just the caller's shared object. */
def = symlook_obj(name, hash, obj, true);
else { /* All the shared objects after the caller's */
while ((obj = obj->next) != NULL)
if ((def = symlook_obj(name, hash, obj, true)) != NULL)
break;
}
} else {
if ((obj = dlcheck(handle)) == NULL)
return NULL;
if (obj->mainprog) {
/* Search main program and all libraries loaded by it. */
for ( ; obj != *main_tail; obj = obj->next)
if ((def = symlook_obj(name, hash, obj, true)) != NULL)
break;
} 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);
}
}
if (def != NULL)
return obj->relocbase + def->st_value;
_rtld_error("Undefined symbol \"%s\"", name);
return NULL;
}
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.
*/
void
r_debug_state(void)
{
}
/*
* 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)
{
unsigned long symnum = obj->buckets[hash % obj->nbuckets];
while (symnum != STN_UNDEF) {
const Elf_Sym *symp;
const char *strp;
assert(symnum < obj->nchains);
symp = obj->symtab + symnum;
assert(symp->st_name != 0);
strp = obj->strtab + symp->st_name;
if (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;
}
}
}
}
static void
unref_object_dag(Obj_Entry *root)
{
assert(root->refcount != 0);
root->refcount--;
if (root->refcount == 0) {
const Needed_Entry *needed;
for (needed = root->needed; needed != NULL; needed = needed->next)
unref_object_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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