/* * Copyright (c) 1999 University of Utah and the Flux Group. * All rights reserved. * * This file is part of the Flux OSKit. The OSKit is free software, also known * as "open source;" you can redistribute it and/or modify it under the terms * of the GNU General Public License (GPL), version 2, as published by the Free * Software Foundation (FSF). To explore alternate licensing terms, contact * the University of Utah at csl-dist@cs.utah.edu or +1-801-585-3271. * * The OSKit is distributed in the hope that it will be useful, but WITHOUT ANY * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS * FOR A PARTICULAR PURPOSE. See the GPL for more details. You should have * received a copy of the GPL along with the OSKit; see the file COPYING. If * not, write to the FSF, 59 Temple Place #330, Boston, MA 02111-1307, USA. */ /*- * 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 1.1 1999/02/19 15:26:18 stoller Exp stoller $ */ /* * 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" #define END_SYM "end" /* Types. */ typedef void (*func_ptr_type)(); /* * Function declarations. */ static void call_fini_functions(Obj_Entry *); static void call_init_functions(Obj_Entry *); static void die(void); static void digest_dynamic(Obj_Entry *); static Obj_Entry *digest_phdr(const Elf_Phdr *, int, caddr_t); static Obj_Entry *dlcheck(void *); static char *find_library(const char *, const Obj_Entry *); static const char *gethints(void); static 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 void unref_object_dag(Obj_Entry *); void xprintf(const char *, ...); #ifdef RTLDDEBUG static const char *basename(const char *); #endif /* * Uh, not exactly an oskit thing. */ #define mprotect(a, b, c) (0) #define munmap(a, b) sfree(a, b) /* Assembly language entry point for lazy binding. */ extern void _rtld_bind_start(void); /* * Data declarations. */ static char *error_message; /* Message for dlerror(), or NULL */ static bool trust; /* False for setuid and setgid programs */ static char *ld_library_path; /* Environment variable for search path */ 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 */ extern Elf_Dyn _DYNAMIC; /* * Boot the dynamic loader. This entrypoint would be used to initialize * the rtld in a newly booted oskit kernel. The caller passes in the name * of the a.out file from which to grab the dynamic load information. */ int oskit_boot_rtld(char *filename) { int phnum; caddr_t entry; Elf_Phdr *phdr; static int done; if (done) return 0; done = 1; trust = 1; rtld_debug = 1; if ((ld_library_path = getenv("LD_LIBRARY_PATH")) == NULL) ld_library_path = "."; dbg("oskit_boot_rtld: LD_LIBRARY_PATH = %s\n", ld_library_path); /* Make the object list empty */ obj_list = NULL; obj_tail = &obj_list; if (&_DYNAMIC != 0) { obj_main = CNEW(Obj_Entry); if (obj_main == NULL) die(); obj_main->dynamic = (const Elf_Dyn *) &_DYNAMIC; obj_main->relocbase = 0; obj_main->path = "Oskit Kernel"; } else if (filename && (phdr = load_headers(filename, &phnum, &entry)) != NULL) { obj_main = digest_phdr(phdr, phnum, entry); if (obj_main == NULL) die(); obj_main->path = xstrdup(filename); } else { /* * This is okay. Won't be able to link against main * program symbols, which will eventually result in * failure. */ return 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++; return 0; } /* * Initialize the dynamic loader. This entrypoint is used when intializing * the library as part of a shared object. The kernel has loaded and linked * the new shared object, but in order to initiate subsequent loads, we need * to have the object list. We could recreate it, but for now the kernel * just passes in the object list. This is rather bogus, since we do not * want to share the object list with the kernel, cause it might get modified * here. But, lets do this for now and see where it takes us. * * How is this supposed to work? Well, when a dynamic link program is loaded * by the FreeBSD kernel, it really loads a PIC version of the rtld library, * that has been linked with a PIC version of the C library. This library * relocates itself, and then loads/relocates the program that is really being * run. We could do something like that too, but it sounds like overkill * unless we really want to play with using different memory allocators, in * which case the object list cannot be shared with the oskit kernel. */ int oskit_init_rtld(Obj_Entry *obj) { static int done; if (done) return 0; done = 1; trust = 1; rtld_debug = 1; if ((ld_library_path = getenv("LD_LIBRARY_PATH")) == NULL) ld_library_path = "."; dbg("oskit_init_rtld: LD_LIBRARY_PATH = %s\n", ld_library_path); if (obj) { /* * Scan down the list to find the last object. */ obj_list = obj; while (obj->next) obj = obj->next; obj_tail = &obj->next; } else { /* Make the object list empty */ obj_list = NULL; obj_tail = &obj_list; } return 0; } caddr_t _rtld_bind(const Obj_Entry *obj, Elf_Word reloff) { const Elf_Rel *rel; const Elf_Sym *def; const Obj_Entry *defobj; Elf_Addr *where; caddr_t target; if (obj->pltrel) rel = (const Elf_Rel *) ((caddr_t) obj->pltrel + reloff); else rel = (const Elf_Rel *) ((caddr_t) obj->pltrela + reloff); where = (Elf_Addr *) (obj->relocbase + rel->r_offset); def = find_symdef(ELF_R_SYM(rel->r_info), obj, &defobj, true); if (def == NULL) die(); target = (caddr_t) (defobj->relocbase + def->st_value); dbg("\"%s\" in \"%s\" ==> %p in \"%s\"", defobj->strtab + def->st_name, basename(obj->path), target, basename(defobj->path)); *where = (Elf_Addr) target; return target; } /* * Error reporting function. Use it like printf. If formats the message * into a buffer, and sets things up so that the next call to dlerror() * will return the message. */ void _rtld_error(const char *fmt, ...) { static char buf[512]; va_list ap; va_start(ap, fmt); vsnprintf(buf, sizeof buf, fmt, ap); error_message = buf; va_end(ap); } #ifdef RTLDDEBUG static const char * basename(const char *name) { const char *p = strrchr(name, '/'); return p != NULL ? p + 1 : name; } #endif static void call_fini_functions(Obj_Entry *first) { Obj_Entry *obj; for (obj = first; obj != NULL; obj = obj->next) if (obj->fini != NULL) (*obj->fini)(); } static void call_init_functions(Obj_Entry *first) { if (first != NULL) { call_init_functions(first->next); if (first->init != NULL) (*first->init)(); } } static void die(void) { const char *msg = dlerror(); if (msg == NULL) msg = "Fatal error"; errx(1, "%s", msg); } /* * Process a shared object's DYNAMIC section, and save the important * information in its Obj_Entry structure. */ static void digest_dynamic(Obj_Entry *obj) { const Elf_Dyn *dynp; Needed_Entry **needed_tail = &obj->needed; const Elf_Dyn *dyn_rpath = NULL; int plttype = DT_REL; for (dynp = obj->dynamic; dynp->d_tag != DT_NULL; dynp++) { switch (dynp->d_tag) { case DT_REL: obj->rel = (const Elf_Rel *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_RELSZ: obj->relsize = dynp->d_un.d_val; break; case DT_RELENT: assert(dynp->d_un.d_val == sizeof(Elf_Rel)); break; case DT_JMPREL: obj->pltrel = (const Elf_Rel *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_PLTRELSZ: obj->pltrelsize = dynp->d_un.d_val; break; case DT_RELA: obj->rela = (const Elf_Rela *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_RELASZ: obj->relasize = dynp->d_un.d_val; break; case DT_RELAENT: assert(dynp->d_un.d_val == sizeof(Elf_Rela)); break; case DT_PLTREL: plttype = dynp->d_un.d_val; assert(dynp->d_un.d_val == DT_REL || plttype == DT_RELA); break; case DT_SYMTAB: obj->symtab = (const Elf_Sym *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_SYMENT: assert(dynp->d_un.d_val == sizeof(Elf_Sym)); break; case DT_STRTAB: obj->strtab = (const char *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_STRSZ: obj->strsize = dynp->d_un.d_val; break; case DT_HASH: { const Elf_Addr *hashtab = (const Elf_Addr *) (obj->relocbase + dynp->d_un.d_ptr); obj->nbuckets = hashtab[0]; obj->nchains = hashtab[1]; obj->buckets = hashtab + 2; obj->chains = obj->buckets + obj->nbuckets; } break; case DT_NEEDED: assert(!obj->rtld); { Needed_Entry *nep = NEW(Needed_Entry); nep->name = dynp->d_un.d_val; nep->obj = NULL; nep->next = NULL; *needed_tail = nep; needed_tail = &nep->next; } break; case DT_PLTGOT: obj->got = (Elf_Addr *) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_TEXTREL: obj->textrel = true; break; case DT_SYMBOLIC: obj->symbolic = true; break; case DT_RPATH: /* * We have to wait until later to process this, because we * might not have gotten the address of the string table yet. */ dyn_rpath = dynp; break; case DT_SONAME: /* Not used by the dynamic linker. */ break; case DT_INIT: obj->init = (void (*)(void)) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_FINI: obj->fini = (void (*)(void)) (obj->relocbase + dynp->d_un.d_ptr); break; case DT_DEBUG: /* XXX - not implemented yet */ dbg("DT_DEBUG not supported!"); break; default: xprintf("Ignored d_tag %d\n",dynp->d_tag); break; } } obj->traced = false; if (plttype == DT_RELA) { obj->pltrela = (const Elf_Rela *) obj->pltrel; obj->pltrel = NULL; obj->pltrelasize = obj->pltrelsize; obj->pltrelsize = 0; } if (dyn_rpath != NULL) obj->rpath = obj->strtab + dyn_rpath->d_un.d_val; } /* * Process a shared object's program header. This is used only for the * main program, when the kernel has already loaded the main program * into memory before calling the dynamic linker. It creates and * returns an Obj_Entry structure. */ static Obj_Entry * digest_phdr(const Elf_Phdr *phdr, int phnum, caddr_t entry) { Obj_Entry *obj = CNEW(Obj_Entry); const Elf_Phdr *phlimit = phdr + phnum; const Elf_Phdr *ph; int nsegs = 0; for (ph = phdr; ph < phlimit; ph++) { switch (ph->p_type) { case PT_PHDR: /*assert((const Elf_Phdr *) ph->p_vaddr == phdr);*/ obj->phdr = (const Elf_Phdr *) ph->p_vaddr; obj->phsize = ph->p_memsz; break; case PT_LOAD: assert(nsegs < 2); if (nsegs == 0) { /* First load segment */ obj->vaddrbase = trunc_page(ph->p_vaddr); obj->mapbase = (caddr_t) obj->vaddrbase; obj->relocbase = obj->mapbase - obj->vaddrbase; obj->textsize = round_page(ph->p_vaddr + ph->p_memsz) - obj->vaddrbase; } else { /* Last load segment */ obj->mapsize = round_page(ph->p_vaddr + ph->p_memsz) - obj->vaddrbase; } nsegs++; break; case PT_DYNAMIC: obj->dynamic = (const Elf_Dyn *) ph->p_vaddr; break; } } assert(nsegs == 2); obj->entry = entry; return obj; } static Obj_Entry * dlcheck(void *handle) { Obj_Entry *obj; for (obj = obj_list; obj != NULL; obj = obj->next) if (obj == (Obj_Entry *) handle) break; if (obj == NULL || obj->dl_refcount == 0) { _rtld_error("Invalid shared object handle %p", handle); return NULL; } return obj; } /* * Hash function for symbol table lookup. Don't even think about changing * this. It is specified by the System V ABI. */ unsigned long elf_hash(const char *name) { const unsigned char *p = (const unsigned char *) name; unsigned long h = 0; unsigned long g; while (*p != '\0') { h = (h << 4) + *p++; if ((g = h & 0xf0000000) != 0) h ^= g >> 24; h &= ~g; } return h; } /* * Find the library with the given name, and return its full pathname. * The returned string is dynamically allocated. Generates an error * message and returns NULL if the library cannot be found. * * If the second argument is non-NULL, then it refers to an already- * loaded shared object, whose library search path will be searched. * * The search order is: * LD_LIBRARY_PATH * ldconfig hints * rpath in the referencing file * /usr/lib */ static char * find_library(const char *name, const Obj_Entry *refobj) { char *pathname; if (strchr(name, '/') != NULL) { /* Hard coded pathname */ if (name[0] != '/' && !trust) { _rtld_error("Absolute pathname required for shared object \"%s\"", name); return NULL; } return xstrdup(name); } dbg(" Searching for \"%s\"", name); if ((pathname = search_library_path(name, ld_library_path)) != NULL || (pathname = search_library_path(name, gethints())) != NULL || (refobj != NULL && (pathname = search_library_path(name, refobj->rpath)) != NULL) || (pathname = search_library_path(name, STANDARD_LIBRARY_PATH)) != NULL) return pathname; _rtld_error("Shared object \"%s\" not found", name); return NULL; } /* * Given a symbol number in a referencing object, find the corresponding * definition of the symbol. Returns a pointer to the symbol, or NULL if * no definition was found. Returns a pointer to the Obj_Entry of the * defining object via the reference parameter DEFOBJ_OUT. */ const Elf_Sym * find_symdef(unsigned long symnum, const Obj_Entry *refobj, const Obj_Entry **defobj_out, bool in_plt) { const Elf_Sym *ref; const Elf_Sym *strongdef; const Elf_Sym *weakdef; const Obj_Entry *obj; const Obj_Entry *strongobj; const Obj_Entry *weakobj; const char *name; unsigned long hash; ref = refobj->symtab + symnum; name = refobj->strtab + ref->st_name; hash = elf_hash(name); if (refobj->symbolic) { /* Look first in the referencing object */ const Elf_Sym *def = symlook_obj(name, hash, refobj, in_plt); if (def != NULL) { *defobj_out = refobj; return def; } } /* * Look in all loaded objects. Skip the referencing object, if * we have already searched it. We keep track of the first weak * definition and the first strong definition we encounter. If * we find a strong definition we stop searching, because there * won't be anything better than that. */ strongdef = weakdef = NULL; strongobj = weakobj = NULL; for (obj = obj_list; obj != NULL; obj = obj->next) { if (obj != refobj || !refobj->symbolic) { const Elf_Sym *def = symlook_obj(name, hash, obj, in_plt); if (def != NULL) { if (ELF_ST_BIND(def->st_info) == STB_WEAK) { if (weakdef == NULL) { weakdef = def; weakobj = obj; } } else { strongdef = def; strongobj = obj; break; /* We are done. */ } } } } if (strongdef != NULL) { *defobj_out = strongobj; return strongdef; } if (weakdef != NULL) { *defobj_out = weakobj; return weakdef; } _rtld_error("%s: Undefined symbol \"%s\"", refobj->path, name); return NULL; } /* * Return the search path from the ldconfig hints file, reading it if * necessary. Returns NULL if there are problems with the hints file, * or if the search path there is empty. */ static const char * gethints(void) { static char *hints; if (hints == NULL) { int fd; struct elfhints_hdr hdr; char *p; /* Keep from trying again in case the hints file is bad. */ hints = ""; if ((fd = open(_PATH_ELF_HINTS, O_RDONLY)) == -1) return NULL; if (read(fd, &hdr, sizeof hdr) != sizeof hdr || hdr.magic != ELFHINTS_MAGIC || hdr.version != 1) { close(fd); return NULL; } p = xmalloc(hdr.dirlistlen + 1); if (lseek(fd, hdr.strtab + hdr.dirlist, SEEK_SET) == -1 || read(fd, p, hdr.dirlistlen + 1) != hdr.dirlistlen + 1) { free(p); close(fd); return NULL; } hints = p; close(fd); } return hints[0] != '\0' ? hints : NULL; } /* * 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; } /* * 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 = read_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 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) { 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)) return -1; if (obj->textrel) { /* Re-protected the text segment. */ if (mprotect(obj->mapbase, obj->textsize, PROT_READ|PROT_EXEC) == -1) { _rtld_error("%s: Cannot write-protect text segment: %s", obj->path, strerror(errno)); return -1; } } /* Process the PLT relocations. */ if (reloc_plt(obj, bind_now)) return -1; /* * Set up the magic number and version in the Obj_Entry. These * were checked in the crt1.o from the original ElfKit, so we * set them for backward compatibility. */ obj->magic = RTLD_MAGIC; obj->version = RTLD_VERSION; /* Set the special GOT entries. */ if (obj->got) { #ifdef __i386__ obj->got[1] = (Elf_Addr) obj; obj->got[2] = (Elf_Addr) &_rtld_bind_start; #endif #ifdef __alpha__ /* This function will be called to perform the relocation. */ obj->got[2] = (Elf_Addr) &_rtld_bind_start; /* Identify this shared object */ obj->got[3] = (Elf_Addr) obj; #endif } } return 0; } /* * Cleanup procedure. It will be called (by the atexit mechanism) just * before the process exits. */ static void rtld_exit(void) { dbg("rtld_exit()"); call_fini_functions(obj_list->next); } static char * search_library_path(const char *name, const char *path) { size_t namelen = strlen(name); const char *p = path; if (p == NULL) return NULL; p += strspn(p, ":;"); while (*p != '\0') { size_t len = strcspn(p, ":;"); if (*p == '/' || trust) { char *pathname; const char *dir = p; size_t dirlen = len; pathname = xmalloc(dirlen + 1 + namelen + 1); strncpy(pathname, dir, dirlen); pathname[dirlen] = '/'; strcpy(pathname + dirlen + 1, name); dbg(" Trying \"%s\"", pathname); if (access(pathname, F_OK) == 0) /* We found it */ return pathname; free(pathname); } p += len; p += strspn(p, ":;"); } return NULL; } int dlclose(void *handle) { Obj_Entry *root = dlcheck(handle); if (root == NULL) return -1; 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; } obj_tail = linkp; } 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; mode = RTLD_LAZY; if (name == NULL) obj = obj_main; else { char *path = find_library(name, NULL); if (path != NULL) obj = load_object(path); } if (obj) { obj->dl_refcount++; if (*old_obj_tail != NULL) { /* We loaded something new. */ assert(*old_obj_tail == obj); /* XXX - Clean up properly after an error. */ if (load_needed_objects(obj) == -1) { obj->dl_refcount--; obj = NULL; } else if (relocate_objects(obj, mode == RTLD_NOW) == -1) { obj->dl_refcount--; obj = NULL; } else call_init_functions(obj); } } 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; } /* * This entrypoint is intended to load a self contained object file into * its own space. That is, it is *not* linked against the current object * file, but starts out new. To accomplish this, I just rebind the obj * list to null, load the specified file, and then restore the list of * objects. The new object list is returned to the caller so that it can * "unload" the object when it exits. Other values are also returned: * 1) The location of the requested entrypoint. 2) A pointer to the program * header, which is passed to the new program so it can do its own rtld * initialization (the program header is part of the text region). * * XXX: Locking ... */ void * dlload(const char *filename, const char *entryname, void **entrypoint, void **phdr) { Obj_Entry **old_obj_tail, *old_obj_list; Obj_Entry *obj = NULL; const Elf_Sym *def; int fd; char *path; if ((path = find_library(filename, NULL)) == NULL) { _rtld_error("Cannot open \"%s\"", filename); return NULL; } /* Save off the old object list. */ old_obj_list = obj_list; old_obj_tail = obj_tail; /* Make the object list empty for the duration of this load. */ obj_list = NULL; obj_tail = &obj_list; /* * open the file, and read it in. */ if ((fd = open(path, O_RDONLY)) == -1) { _rtld_error("Cannot open \"%s\"", path); goto bad; } obj = read_object(fd); close(fd); if (obj == NULL) goto bad; obj->refcount++; obj->path = path; *obj_tail = obj; obj_tail = &obj->next; digest_dynamic(obj); dbg(" %p .. %p: %s", obj->mapbase, obj->mapbase + obj->mapsize - 1, obj->path); /* * Load any needed objects. */ if (load_needed_objects(obj) == -1) { dbg("dlload: %s - Could not load needed objects\n", filename); goto bad; } /* * Relocate newly loaded object. */ if (relocate_objects(obj, false) == -1) { dbg("dlload: %s - Could not relocate\n", filename); goto bad; } /* * Find the desired entrypoint. */ if ((def = symlook_obj(entryname, elf_hash(entryname), obj, true)) == NULL) { dbg("dlload: %s - Could not find entrypoint %s\n", filename, entryname); goto bad; } obj->dl_refcount++; *entrypoint = obj->relocbase + def->st_value; *phdr = obj->mapbase; /* Restore the old object list */ obj_list = old_obj_list; obj_tail = old_obj_tail; return obj; bad: /* * Free up all the object information. */ for (obj = obj_list; obj != NULL; ) { Obj_Entry *nextobj = obj->next; sfree(obj->mapbase, obj->mapsize); free(obj->path); free(obj); obj = nextobj; } /* Restore the old object list */ obj_list = old_obj_list; obj_tail = old_obj_tail; return 0; } /* * Unload a shared object (and any other related shared objects). */ int dlunload(void *handle) { Obj_Entry *obj = handle; assert(obj); obj->dl_refcount--; unref_object_dag(obj); /* * Free up all the object information. */ for (; obj != NULL; ) { Obj_Entry *nextobj = obj->next; assert(obj->refcount == 0); sfree(obj->mapbase, obj->mapsize); free(obj->path); free(obj); obj = nextobj; } return 0; } /* * Search the symbol table of a single shared object for a symbol of * the given name. Returns a pointer to the symbol, or NULL if no * definition was found. * * The symbol's hash value is passed in for efficiency reasons; that * eliminates many recomputations of the hash value. */ const Elf_Sym * symlook_obj(const char *name, unsigned long hash, const Obj_Entry *obj, bool in_plt) { unsigned long symnum = obj->buckets[hash % obj->nbuckets]; while (symnum != STN_UNDEF) { const Elf_Sym *symp; const char *strp; assert(symnum < obj->nchains); symp = obj->symtab + symnum; assert(symp->st_name != 0); strp = obj->strtab + symp->st_name; if (strcmp(name, strp) == 0) return symp->st_shndx != SHN_UNDEF || (!in_plt && symp->st_value != 0 && ELF_ST_TYPE(symp->st_info) == STT_FUNC) ? symp : NULL; symnum = obj->chains[symnum]; } return NULL; } static void 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); }