freebsd-skq/libexec/rtld-elf/rtld.c
John Polstra 962fdc466a Fix a serious performance bug for large programs on the Alpha,
discovered by Hidetoshi Shimokawa.  Large programs need multiple
GOTs.  The lazy binding stub in the PLT can be reached from any of
these GOTs, but the dynamic linker only has enough information to
fix up the first GOT entry.  Thus calls through the other GOTs went
through the time-consuming lazy binding process on every call.

This fix rewrites the PLT entries themselves to bypass the lazy
binding.

Tested by Hidetoshi Shimokawa and Steve Price.

Reviewed by:	Doug Rabson <dfr@freebsd.org>
1999-06-25 02:53:59 +00:00

1532 lines
38 KiB
C

/*-
* Copyright 1996, 1997, 1998, 1999 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 1.23 1999/04/22 01:54:38 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 const char *basename(const char *);
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 set_program_var(const char *, const void *);
static void unref_object_dag(Obj_Entry *);
static void trace_loaded_objects(Obj_Entry *obj);
void r_debug_state(void);
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 **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 */
static Elf_Sym sym_zero; /* For resolving undefined weak refs. */
#define GDB_STATE(s) r_debug.r_state = s; r_debug_state();
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,
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);
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);
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] ? argv[0] : "(null)");
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++;
/* 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();
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("initializing key program variables");
set_program_var("__progname", argv[0] != NULL ? basename(argv[0]) : "");
set_program_var("environ", env);
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;
}
Elf_Addr
_rtld_bind(const Obj_Entry *obj, Elf_Word reloff)
{
const Elf_Rel *rel;
const Elf_Sym *def;
const Obj_Entry *defobj;
Elf_Addr *where;
Elf_Addr 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 = (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);
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);
}
static const char *
basename(const char *name)
{
const char *p = strrchr(name, '/');
return p != NULL ? p + 1 : name;
}
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:
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 = (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 ((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)
{
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;
}
if (ELF_ST_BIND(ref->st_info) == STB_WEAK) {
*defobj_out = obj_main;
return &sym_zero;
}
_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;
#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;
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 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)
{
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;
}
obj_tail = linkp;
}
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, obj_main);
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;
}
int
dladdr(const void *addr, Dl_info *info)
{
const Obj_Entry *obj;
const Elf_Sym *def;
void *symbol_addr;
unsigned long symoffset;
obj = obj_from_addr(addr);
if (obj == NULL) {
_rtld_error("No shared object contains address");
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;
}
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.
*/
void
r_debug_state(void)
{
}
/*
* 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;
}
}
}
/*
* 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;
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);
}