/*- * 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 1.18 1998/03/06 22:14:54 jdp Exp $ */ /* * 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 "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 Elf32_Phdr *, int, caddr_t); static Obj_Entry *dlcheck(void *); static int do_copy_relocations(Obj_Entry *); static unsigned long elf_hash(const char *); static char *find_library(const char *, const Obj_Entry *); static const Elf32_Sym *find_symdef(unsigned long, const Obj_Entry *, const Obj_Entry **, bool); static void init_rtld(caddr_t); static bool is_exported(const Elf32_Sym *); static int load_needed_objects(Obj_Entry *); 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 const Elf32_Sym *symlook_obj(const char *, unsigned long, const Obj_Entry *, bool); static void unref_object_dag(Obj_Entry *); 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() \ ({ Elf32_Addr *thegot; \ __asm__("movl %%ebx,%0" : "=rm"(thegot)); \ thegot; }) #else #error "This file only supports the i386 architecture" #endif /* * Data declarations. */ static char *error_message; /* Message for dlerror(), or NULL */ 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 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 */ /* * 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. * * The return value is the main program's entry point. */ func_ptr_type _rtld(Elf32_Word *sp, func_ptr_type *exit_proc) { Elf32_Auxinfo *aux_info[AT_COUNT]; int i; int argc; char **argv; char **env; Elf32_Auxinfo *aux; Elf32_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 = (Elf32_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"); } 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 Elf32_Phdr *phdr; int phnum; caddr_t entry; dbg("processing main program's program header"); assert(aux_info[AT_PHDR] != NULL); phdr = (const Elf32_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(Elf32_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); /* Link the main program into the list of objects. */ *obj_tail = obj_main; obj_tail = &obj_main->next; obj_main->refcount++; dbg("loading needed objects"); if (load_needed_objects(obj_main) == -1) die(); 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); /* Return the exit procedure and the program entry point. */ *exit_proc = (func_ptr_type) rtld_exit; return (func_ptr_type) obj_main->entry; } caddr_t _rtld_bind(const Obj_Entry *obj, Elf32_Word reloff) { const Elf32_Rel *rel; const Elf32_Sym *def; const Obj_Entry *defobj; Elf32_Addr *where; caddr_t target; rel = (const Elf32_Rel *) ((caddr_t) obj->pltrel + reloff); assert(ELF32_R_TYPE(rel->r_info) == R_386_JMP_SLOT); where = (Elf32_Addr *) (obj->relocbase + rel->r_offset); def = find_symdef(ELF32_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 = (Elf32_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 Elf32_Dyn *dynp; Needed_Entry **needed_tail = &obj->needed; const Elf32_Dyn *dyn_rpath = NULL; for (dynp = obj->dynamic; dynp->d_tag != DT_NULL; dynp++) { switch (dynp->d_tag) { case DT_REL: obj->rel = (const Elf32_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(Elf32_Rel)); break; case DT_JMPREL: obj->pltrel = (const Elf32_Rel *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_PLTRELSZ: obj->pltrelsize = dynp->d_un.d_val; break; case DT_RELA: case DT_RELASZ: case DT_RELAENT: assert(0); /* Should never appear for i386 */ break; case DT_PLTREL: assert(dynp->d_un.d_val == DT_REL); /* For the i386 */ break; case DT_SYMTAB: obj->symtab = (const Elf32_Sym *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_SYMENT: assert(dynp->d_un.d_val == sizeof(Elf32_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 Elf32_Word *hashtab = (const Elf32_Word *) (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 = (Elf32_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 */ break; } } 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 Elf32_Phdr *phdr, int phnum, caddr_t entry) { Obj_Entry *obj = CNEW(Obj_Entry); const Elf32_Phdr *phlimit = phdr + phnum; const Elf32_Phdr *ph; int nsegs = 0; for (ph = phdr; ph < phlimit; ph++) { switch (ph->p_type) { case PT_PHDR: assert((const Elf32_Phdr *) ph->p_vaddr == phdr); obj->phdr = (const Elf32_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 Elf32_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; } /* * Process the special R_386_COPY relocations in the main program. These * copy data from a shared object into a region in the main program's BSS * segment. * * Returns 0 on success, -1 on failure. */ static int do_copy_relocations(Obj_Entry *dstobj) { const Elf32_Rel *rellim; const Elf32_Rel *rel; assert(dstobj->mainprog); /* COPY relocations are invalid elsewhere */ rellim = (const Elf32_Rel *) ((caddr_t) dstobj->rel + dstobj->relsize); for (rel = dstobj->rel; rel < rellim; rel++) { if (ELF32_R_TYPE(rel->r_info) == R_386_COPY) { void *dstaddr; const Elf32_Sym *dstsym; const char *name; unsigned long hash; size_t size; const void *srcaddr; const Elf32_Sym *srcsym; Obj_Entry *srcobj; dstaddr = (void *) (dstobj->relocbase + rel->r_offset); dstsym = dstobj->symtab + ELF32_R_SYM(rel->r_info); name = dstobj->strtab + dstsym->st_name; hash = elf_hash(name); size = dstsym->st_size; for (srcobj = dstobj->next; srcobj != NULL; srcobj = srcobj->next) if ((srcsym = symlook_obj(name, hash, srcobj, false)) != NULL) break; if (srcobj == NULL) { _rtld_error("Undefined symbol \"%s\" referenced from COPY" " relocation in %s", name, dstobj->path); return -1; } srcaddr = (const void *) (srcobj->relocbase + srcsym->st_value); memcpy(dstaddr, srcaddr, size); } } return 0; } /* * Hash function for symbol table lookup. Don't even think about changing * this. It is specified by the System V ABI. */ static 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. */ 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, 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. */ static const Elf32_Sym * find_symdef(unsigned long symnum, const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt) { const Elf32_Sym *ref; const Elf32_Sym *strongdef; const Elf32_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 Elf32_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 Elf32_Sym *def = symlook_obj(name, hash, obj, in_plt); if (def != NULL) { if (ELF32_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 Elf32_Sym *def = symlook_obj(name, hash, &obj_rtld, in_plt); if (def != NULL && is_exported(def)) { if (ELF32_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; } /* * 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. */ 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(); obj_rtld.dynamic = (const Elf32_Dyn *) (obj_rtld.mapbase + obj_rtld.got[0]); 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; } static bool is_exported(const Elf32_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); if (path == NULL) return -1; needed->obj = load_object(path); if (needed->obj == NULL) return -1; /* XXX - cleanup */ } } 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; 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 Elf32_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) { const Elf32_Rel *rellim; const Elf32_Rel *rel; 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. */ rellim = (const Elf32_Rel *) ((caddr_t) obj->rel + obj->relsize); for (rel = obj->rel; rel < rellim; rel++) { Elf32_Addr *where = (Elf32_Addr *) (obj->relocbase + rel->r_offset); switch (ELF32_R_TYPE(rel->r_info)) { case R_386_NONE: break; case R_386_32: { const Elf32_Sym *def; const Obj_Entry *defobj; def = find_symdef(ELF32_R_SYM(rel->r_info), obj, &defobj, false); if (def == NULL) return -1; *where += (Elf32_Addr) (defobj->relocbase + def->st_value); } break; case R_386_PC32: /* * I don't think the dynamic linker should ever see this * type of relocation. But the binutils-2.6 tools sometimes * generate it. */ { const Elf32_Sym *def; const Obj_Entry *defobj; def = find_symdef(ELF32_R_SYM(rel->r_info), obj, &defobj, false); if (def == NULL) return -1; *where += (Elf32_Addr) (defobj->relocbase + def->st_value) - (Elf32_Addr) where; } break; case R_386_COPY: /* * These are deferred until all other relocations have * been done. All we do here is make sure that the COPY * relocation is not in a shared library. They are allowed * only in executable files. */ if (!obj->mainprog) { _rtld_error("%s: Unexpected R_386_COPY relocation" " in shared library", obj->path); return -1; } break; case R_386_GLOB_DAT: { const Elf32_Sym *def; const Obj_Entry *defobj; def = find_symdef(ELF32_R_SYM(rel->r_info), obj, &defobj, false); if (def == NULL) return -1; *where = (Elf32_Addr) (defobj->relocbase + def->st_value); } break; case R_386_RELATIVE: *where += (Elf32_Addr) obj->relocbase; break; default: _rtld_error("%s: Unsupported relocation type %d" " in non-PLT relocations\n", obj->path, ELF32_R_TYPE(rel->r_info)); 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. */ rellim = (const Elf32_Rel *) ((caddr_t) obj->pltrel + obj->pltrelsize); if (bind_now) { /* Fully resolve procedure addresses now */ for (rel = obj->pltrel; rel < rellim; rel++) { Elf32_Addr *where = (Elf32_Addr *) (obj->relocbase + rel->r_offset); const Elf32_Sym *def; const Obj_Entry *defobj; assert(ELF32_R_TYPE(rel->r_info) == R_386_JMP_SLOT); def = find_symdef(ELF32_R_SYM(rel->r_info), obj, &defobj, true); if (def == NULL) return -1; *where = (Elf32_Addr) (defobj->relocbase + def->st_value); } } else { /* Just relocate the GOT slots pointing into the PLT */ for (rel = obj->pltrel; rel < rellim; rel++) { Elf32_Addr *where = (Elf32_Addr *) (obj->relocbase + rel->r_offset); *where += (Elf32_Addr) obj->relocbase; } } /* * 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. */ obj->got[1] = (Elf32_Addr) obj; obj->got[2] = (Elf32_Addr) &_rtld_bind_start; } 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; 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); } *linkp = obj->next; free(obj); } else linkp = &obj->next; } } 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; if (name == NULL) obj = obj_main; else { char *path = find_library(name, NULL); if (path == NULL) return NULL; obj = load_object(path); if (obj == NULL) return NULL; } 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) return NULL; if (relocate_objects(obj, mode == RTLD_NOW) == -1) return NULL; call_init_functions(obj); } return obj; } void * dlsym(void *handle, const char *name) { const Obj_Entry *obj; unsigned long hash; const Elf32_Sym *def; hash = elf_hash(name); if (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; } def = NULL; while ((obj = obj->next) != NULL) if ((def = symlook_obj(name, hash, obj, true)) != NULL) break; } else { if ((obj = dlcheck(handle)) == NULL) return NULL; /* * 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; } /* * 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. */ static const Elf32_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 Elf32_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 && ELF32_ST_TYPE(symp->st_info) == STT_FUNC) ? symp : NULL; symnum = obj->chains[symnum]; } return NULL; } 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); }