/*- * 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. * * $FreeBSD$ */ /* * Dynamic linker for ELF. * * John Polstra . */ #ifndef __GNUC__ #error "GCC is needed to compile this file" #endif #include #include #include #include #include #include #include #include #include #include #include #include #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" #define PATH_RTLD "/usr/libexec/ld-elf.so.1" /* 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, const char *); static Obj_Entry *dlcheck(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); 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 void objlist_add(Objlist *, Obj_Entry *); static Objlist_Entry *objlist_find(Objlist *, const Obj_Entry *); static void objlist_remove(Objlist *, Obj_Entry *); 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_list(const char *, unsigned long, Objlist *, const Obj_Entry **, bool in_plt); static void trace_loaded_objects(Obj_Entry *obj); static void unload_object(Obj_Entry *, bool do_fini_funcs); static void unref_dag(Obj_Entry *); 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 *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 long curmark; /* Current mark value */ 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 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; const char *argv0; Obj_Entry *obj; /* * 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_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(); for (obj = obj_list; obj != NULL; obj = obj->next) objlist_add(&list_main, obj); 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); r_debug_state(); /* say hello to gdb! */ dbg("calling _init functions"); call_init_functions(obj_main->next); 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; 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: 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->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, Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt) { const Elf_Sym *ref; const Elf_Sym *def; const Elf_Sym *symp; const Obj_Entry *obj; const Obj_Entry *defobj; const Objlist_Entry *elm; const char *name; unsigned long hash; ref = refobj->symtab + symnum; name = refobj->strtab + ref->st_name; hash = elf_hash(name); def = NULL; defobj = NULL; curmark++; if (refobj->symbolic) { /* Look first in the referencing object */ symp = symlook_obj(name, hash, refobj, in_plt); refobj->mark = curmark; 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); 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); 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); 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 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; 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) { curmark++; init_dag1(root, root); } static void init_dag1(Obj_Entry *root, Obj_Entry *obj) { const Needed_Entry *needed; if (obj->mark == curmark) return; obj->mark = curmark; objlist_add(&obj->dldags, root); objlist_add(&root->dagmembers, obj); for (needed = obj->needed; needed != NULL; needed = needed->next) if (needed->obj != NULL) init_dag1(root, needed->obj); } /* * 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; 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; 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; 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; } static void objlist_add(Objlist *list, Obj_Entry *obj) { Objlist_Entry *elm; elm = NEW(Objlist_Entry); elm->obj = obj; STAILQ_INSERT_TAIL(list, elm, link); } 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_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); } } /* * 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); unload_object(root, true); root->dl_refcount--; 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; 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_add(&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) { unload_object(obj, false); 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; const Obj_Entry *defobj; hash = elf_hash(name); def = NULL; defobj = 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); defobj = obj; } else { /* All the shared objects after the caller's */ while ((obj = obj->next) != NULL) { if ((def = symlook_obj(name, hash, obj, true)) != NULL) { defobj = obj; break; } } } } else { if ((obj = dlcheck(handle)) == NULL) return NULL; if (obj->mainprog) { /* Search main program and all libraries loaded by it. */ curmark++; def = symlook_list(name, hash, &list_main, &defobj, true); } 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) return defobj->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; } } } static const Elf_Sym * symlook_list(const char *name, unsigned long hash, Objlist *objlist, const Obj_Entry **defobj_out, bool in_plt) { 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 (elm->obj->mark == curmark) continue; elm->obj->mark = curmark; 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 (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; } } } } /* * Note, this is called only for objects loaded by dlopen(). */ static void unload_object(Obj_Entry *root, bool do_fini_funcs) { unref_dag(root); if (root->refcount == 0) { /* We are finished with some objects. */ Obj_Entry *obj; Obj_Entry **linkp; Objlist_Entry *elm; /* Finalize objects that are about to be unmapped. */ if (do_fini_funcs) for (obj = obj_list->next; obj != NULL; obj = obj->next) if (obj->refcount == 0 && obj->fini != NULL) (*obj->fini)(); /* 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_free(obj); } else linkp = &obj->next; } obj_tail = linkp; } } static void unref_dag(Obj_Entry *root) { const Needed_Entry *needed; assert(root->refcount != 0); 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); }