/* * Copyright (C) 2008, 2009 The Android Open Source Project * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 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 COPYRIGHT HOLDERS AND CONTRIBUTORS * "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 * COPYRIGHT OWNER OR CONTRIBUTORS 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. */ #include #include #include #include #include #include #include #include #include #include #include #include // Private C library headers. #include #include #include #include "linker.h" #include "linker_debug.h" #include "linker_environ.h" #include "linker_phdr.h" /* Assume average path length of 64 and max 8 paths */ #define LDPATH_BUFSIZE 512 #define LDPATH_MAX 8 #define LDPRELOAD_BUFSIZE 512 #define LDPRELOAD_MAX 8 /* >>> IMPORTANT NOTE - READ ME BEFORE MODIFYING <<< * * Do NOT use malloc() and friends or pthread_*() code here. * Don't use printf() either; it's caused mysterious memory * corruption in the past. * The linker runs before we bring up libc and it's easiest * to make sure it does not depend on any complex libc features * * open issues / todo: * * - are we doing everything we should for ARM_COPY relocations? * - cleaner error reporting * - after linking, set as much stuff as possible to READONLY * and NOEXEC */ static bool soinfo_link_image(soinfo* si); // We can't use malloc(3) in the dynamic linker. We use a linked list of anonymous // maps, each a single page in size. The pages are broken up into as many struct soinfo // objects as will fit, and they're all threaded together on a free list. #define SOINFO_PER_POOL ((PAGE_SIZE - sizeof(soinfo_pool_t*)) / sizeof(soinfo)) struct soinfo_pool_t { soinfo_pool_t* next; soinfo info[SOINFO_PER_POOL]; }; static struct soinfo_pool_t* gSoInfoPools = NULL; static soinfo* gSoInfoFreeList = NULL; static soinfo* solist = &libdl_info; static soinfo* sonext = &libdl_info; static soinfo* somain; /* main process, always the one after libdl_info */ static const char* const gSoPaths[] = { "/vendor/lib", "/system/lib", NULL }; static char gLdPathsBuffer[LDPATH_BUFSIZE]; static const char* gLdPaths[LDPATH_MAX + 1]; static char gLdPreloadsBuffer[LDPRELOAD_BUFSIZE]; static const char* gLdPreloadNames[LDPRELOAD_MAX + 1]; static soinfo* gLdPreloads[LDPRELOAD_MAX + 1]; __LIBC_HIDDEN__ int gLdDebugVerbosity; __LIBC_HIDDEN__ abort_msg_t* gAbortMessage = NULL; // For debuggerd. enum RelocationKind { kRelocAbsolute = 0, kRelocRelative, kRelocCopy, kRelocSymbol, kRelocMax }; #if STATS struct linker_stats_t { int count[kRelocMax]; }; static linker_stats_t linker_stats; static void count_relocation(RelocationKind kind) { ++linker_stats.count[kind]; } #else static void count_relocation(RelocationKind) { } #endif #if COUNT_PAGES static unsigned bitmask[4096]; #define MARK(offset) \ do { \ bitmask[((offset) >> 12) >> 3] |= (1 << (((offset) >> 12) & 7)); \ } while(0) #else #define MARK(x) do {} while (0) #endif // You shouldn't try to call memory-allocating functions in the dynamic linker. // Guard against the most obvious ones. #define DISALLOW_ALLOCATION(return_type, name, ...) \ return_type name __VA_ARGS__ \ { \ const char* msg = "ERROR: " #name " called from the dynamic linker!\n"; \ __libc_format_log(ANDROID_LOG_FATAL, "linker", "%s", msg); \ write(2, msg, strlen(msg)); \ abort(); \ } #define UNUSED __attribute__((unused)) DISALLOW_ALLOCATION(void*, malloc, (size_t u UNUSED)); DISALLOW_ALLOCATION(void, free, (void* u UNUSED)); DISALLOW_ALLOCATION(void*, realloc, (void* u1 UNUSED, size_t u2 UNUSED)); DISALLOW_ALLOCATION(void*, calloc, (size_t u1 UNUSED, size_t u2 UNUSED)); static char tmp_err_buf[768]; static char __linker_dl_err_buf[768]; char* linker_get_error_buffer() { return &__linker_dl_err_buf[0]; } size_t linker_get_error_buffer_size() { return sizeof(__linker_dl_err_buf); } /* * This function is an empty stub where GDB locates a breakpoint to get notified * about linker activity. */ extern "C" void __attribute__((noinline)) __attribute__((visibility("default"))) rtld_db_dlactivity(); static r_debug _r_debug = {1, NULL, &rtld_db_dlactivity, RT_CONSISTENT, 0}; static link_map_t* r_debug_tail = 0; static pthread_mutex_t gDebugMutex = PTHREAD_MUTEX_INITIALIZER; static void insert_soinfo_into_debug_map(soinfo * info) { // Copy the necessary fields into the debug structure. link_map_t* map = &(info->link_map); map->l_addr = info->base; map->l_name = (char*) info->name; map->l_ld = (uintptr_t)info->dynamic; /* Stick the new library at the end of the list. * gdb tends to care more about libc than it does * about leaf libraries, and ordering it this way * reduces the back-and-forth over the wire. */ if (r_debug_tail) { r_debug_tail->l_next = map; map->l_prev = r_debug_tail; map->l_next = 0; } else { _r_debug.r_map = map; map->l_prev = 0; map->l_next = 0; } r_debug_tail = map; } static void remove_soinfo_from_debug_map(soinfo* info) { link_map_t* map = &(info->link_map); if (r_debug_tail == map) { r_debug_tail = map->l_prev; } if (map->l_prev) { map->l_prev->l_next = map->l_next; } if (map->l_next) { map->l_next->l_prev = map->l_prev; } } static void notify_gdb_of_load(soinfo* info) { if (info->flags & FLAG_EXE) { // GDB already knows about the main executable return; } ScopedPthreadMutexLocker locker(&gDebugMutex); _r_debug.r_state = RT_ADD; rtld_db_dlactivity(); insert_soinfo_into_debug_map(info); _r_debug.r_state = RT_CONSISTENT; rtld_db_dlactivity(); } static void notify_gdb_of_unload(soinfo* info) { if (info->flags & FLAG_EXE) { // GDB already knows about the main executable return; } ScopedPthreadMutexLocker locker(&gDebugMutex); _r_debug.r_state = RT_DELETE; rtld_db_dlactivity(); remove_soinfo_from_debug_map(info); _r_debug.r_state = RT_CONSISTENT; rtld_db_dlactivity(); } void notify_gdb_of_libraries() { _r_debug.r_state = RT_ADD; rtld_db_dlactivity(); _r_debug.r_state = RT_CONSISTENT; rtld_db_dlactivity(); } static bool ensure_free_list_non_empty() { if (gSoInfoFreeList != NULL) { return true; } // Allocate a new pool. soinfo_pool_t* pool = reinterpret_cast(mmap(NULL, sizeof(*pool), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, 0, 0)); if (pool == MAP_FAILED) { return false; } // Add the pool to our list of pools. pool->next = gSoInfoPools; gSoInfoPools = pool; // Chain the entries in the new pool onto the free list. gSoInfoFreeList = &pool->info[0]; soinfo* next = NULL; for (int i = SOINFO_PER_POOL - 1; i >= 0; --i) { pool->info[i].next = next; next = &pool->info[i]; } return true; } static void set_soinfo_pool_protection(int protection) { for (soinfo_pool_t* p = gSoInfoPools; p != NULL; p = p->next) { if (mprotect(p, sizeof(*p), protection) == -1) { abort(); // Can't happen. } } } static soinfo* soinfo_alloc(const char* name) { if (strlen(name) >= SOINFO_NAME_LEN) { DL_ERR("library name \"%s\" too long", name); return NULL; } if (!ensure_free_list_non_empty()) { DL_ERR("out of memory when loading \"%s\"", name); return NULL; } // Take the head element off the free list. soinfo* si = gSoInfoFreeList; gSoInfoFreeList = gSoInfoFreeList->next; // Initialize the new element. memset(si, 0, sizeof(soinfo)); strlcpy(si->name, name, sizeof(si->name)); sonext->next = si; sonext = si; TRACE("name %s: allocated soinfo @ %p", name, si); return si; } static void soinfo_free(soinfo* si) { if (si == NULL) { return; } soinfo *prev = NULL, *trav; TRACE("name %s: freeing soinfo @ %p", si->name, si); for (trav = solist; trav != NULL; trav = trav->next) { if (trav == si) break; prev = trav; } if (trav == NULL) { /* si was not in solist */ DL_ERR("name \"%s\" is not in solist!", si->name); return; } /* prev will never be NULL, because the first entry in solist is always the static libdl_info. */ prev->next = si->next; if (si == sonext) { sonext = prev; } si->next = gSoInfoFreeList; gSoInfoFreeList = si; } static void parse_path(const char* path, const char* delimiters, const char** array, char* buf, size_t buf_size, size_t max_count) { if (path == NULL) { return; } size_t len = strlcpy(buf, path, buf_size); size_t i = 0; char* buf_p = buf; while (i < max_count && (array[i] = strsep(&buf_p, delimiters))) { if (*array[i] != '\0') { ++i; } } // Forget the last path if we had to truncate; this occurs if the 2nd to // last char isn't '\0' (i.e. wasn't originally a delimiter). if (i > 0 && len >= buf_size && buf[buf_size - 2] != '\0') { array[i - 1] = NULL; } else { array[i] = NULL; } } static void parse_LD_LIBRARY_PATH(const char* path) { parse_path(path, ":", gLdPaths, gLdPathsBuffer, sizeof(gLdPathsBuffer), LDPATH_MAX); } static void parse_LD_PRELOAD(const char* path) { // We have historically supported ':' as well as ' ' in LD_PRELOAD. parse_path(path, " :", gLdPreloadNames, gLdPreloadsBuffer, sizeof(gLdPreloadsBuffer), LDPRELOAD_MAX); } #ifdef ANDROID_ARM_LINKER /* For a given PC, find the .so that it belongs to. * Returns the base address of the .ARM.exidx section * for that .so, and the number of 8-byte entries * in that section (via *pcount). * * Intended to be called by libc's __gnu_Unwind_Find_exidx(). * * This function is exposed via dlfcn.cpp and libdl.so. */ _Unwind_Ptr dl_unwind_find_exidx(_Unwind_Ptr pc, int *pcount) { soinfo *si; unsigned addr = (unsigned)pc; for (si = solist; si != 0; si = si->next){ if ((addr >= si->base) && (addr < (si->base + si->size))) { *pcount = si->ARM_exidx_count; return (_Unwind_Ptr)si->ARM_exidx; } } *pcount = 0; return NULL; } #elif defined(ANDROID_X86_LINKER) || defined(ANDROID_MIPS_LINKER) /* Here, we only have to provide a callback to iterate across all the * loaded libraries. gcc_eh does the rest. */ int dl_iterate_phdr(int (*cb)(dl_phdr_info *info, size_t size, void *data), void *data) { int rv = 0; for (soinfo* si = solist; si != NULL; si = si->next) { dl_phdr_info dl_info; dl_info.dlpi_addr = si->link_map.l_addr; dl_info.dlpi_name = si->link_map.l_name; dl_info.dlpi_phdr = si->phdr; dl_info.dlpi_phnum = si->phnum; rv = cb(&dl_info, sizeof(dl_phdr_info), data); if (rv != 0) { break; } } return rv; } #endif static Elf32_Sym* soinfo_elf_lookup(soinfo* si, unsigned hash, const char* name) { Elf32_Sym* s; Elf32_Sym* symtab = si->symtab; const char* strtab = si->strtab; unsigned n; TRACE_TYPE(LOOKUP, "SEARCH %s in %s@0x%08x %08x %d", name, si->name, si->base, hash, hash % si->nbucket); n = hash % si->nbucket; for (n = si->bucket[hash % si->nbucket]; n != 0; n = si->chain[n]) { s = symtab + n; if (strcmp(strtab + s->st_name, name)) continue; /* only concern ourselves with global and weak symbol definitions */ switch(ELF32_ST_BIND(s->st_info)){ case STB_GLOBAL: case STB_WEAK: if (s->st_shndx == SHN_UNDEF) { continue; } TRACE_TYPE(LOOKUP, "FOUND %s in %s (%08x) %d", name, si->name, s->st_value, s->st_size); return s; } } return NULL; } static unsigned elfhash(const char* _name) { const unsigned char* name = (const unsigned char*) _name; unsigned h = 0, g; while(*name) { h = (h << 4) + *name++; g = h & 0xf0000000; h ^= g; h ^= g >> 24; } return h; } static Elf32_Sym* soinfo_do_lookup(soinfo* si, const char* name, soinfo** lsi, soinfo* needed[]) { unsigned elf_hash = elfhash(name); Elf32_Sym* s = NULL; if (si != NULL && somain != NULL) { /* * Local scope is executable scope. Just start looking into it right away * for the shortcut. */ if (si == somain) { s = soinfo_elf_lookup(si, elf_hash, name); if (s != NULL) { *lsi = si; goto done; } } else { /* Order of symbol lookup is controlled by DT_SYMBOLIC flag */ /* * If this object was built with symbolic relocations disabled, the * first place to look to resolve external references is the main * executable. */ if (!si->has_DT_SYMBOLIC) { DEBUG("%s: looking up %s in executable %s", si->name, name, somain->name); s = soinfo_elf_lookup(somain, elf_hash, name); if (s != NULL) { *lsi = somain; goto done; } } /* Look for symbols in the local scope (the object who is * searching). This happens with C++ templates on i386 for some * reason. * * Notes on weak symbols: * The ELF specs are ambiguous about treatment of weak definitions in * dynamic linking. Some systems return the first definition found * and some the first non-weak definition. This is system dependent. * Here we return the first definition found for simplicity. */ s = soinfo_elf_lookup(si, elf_hash, name); if (s != NULL) { *lsi = si; goto done; } /* * If this object was built with -Bsymbolic and symbol is not found * in the local scope, try to find the symbol in the main executable. */ if (si->has_DT_SYMBOLIC) { DEBUG("%s: looking up %s in executable %s after local scope", si->name, name, somain->name); s = soinfo_elf_lookup(somain, elf_hash, name); if (s != NULL) { *lsi = somain; goto done; } } } } /* Next, look for it in the preloads list */ for (int i = 0; gLdPreloads[i] != NULL; i++) { s = soinfo_elf_lookup(gLdPreloads[i], elf_hash, name); if (s != NULL) { *lsi = gLdPreloads[i]; goto done; } } for (int i = 0; needed[i] != NULL; i++) { DEBUG("%s: looking up %s in %s", si->name, name, needed[i]->name); s = soinfo_elf_lookup(needed[i], elf_hash, name); if (s != NULL) { *lsi = needed[i]; goto done; } } done: if (s != NULL) { TRACE_TYPE(LOOKUP, "si %s sym %s s->st_value = 0x%08x, " "found in %s, base = 0x%08x, load bias = 0x%08x", si->name, name, s->st_value, (*lsi)->name, (*lsi)->base, (*lsi)->load_bias); return s; } return NULL; } /* This is used by dlsym(3). It performs symbol lookup only within the specified soinfo object and not in any of its dependencies. TODO: Only looking in the specified soinfo seems wrong. dlsym(3) says that it should do a breadth first search through the dependency tree. This agrees with the ELF spec (aka System V Application Binary Interface) where in Chapter 5 it discuss resolving "Shared Object Dependencies" in breadth first search order. */ Elf32_Sym* dlsym_handle_lookup(soinfo* si, const char* name) { return soinfo_elf_lookup(si, elfhash(name), name); } /* This is used by dlsym(3) to performs a global symbol lookup. If the start value is null (for RTLD_DEFAULT), the search starts at the beginning of the global solist. Otherwise the search starts at the specified soinfo (for RTLD_NEXT). */ Elf32_Sym* dlsym_linear_lookup(const char* name, soinfo** found, soinfo* start) { unsigned elf_hash = elfhash(name); if (start == NULL) { start = solist; } Elf32_Sym* s = NULL; for (soinfo* si = start; (s == NULL) && (si != NULL); si = si->next) { s = soinfo_elf_lookup(si, elf_hash, name); if (s != NULL) { *found = si; break; } } if (s != NULL) { TRACE_TYPE(LOOKUP, "%s s->st_value = 0x%08x, found->base = 0x%08x", name, s->st_value, (*found)->base); } return s; } soinfo* find_containing_library(const void* p) { Elf32_Addr address = reinterpret_cast(p); for (soinfo* si = solist; si != NULL; si = si->next) { if (address >= si->base && address - si->base < si->size) { return si; } } return NULL; } Elf32_Sym* dladdr_find_symbol(soinfo* si, const void* addr) { Elf32_Addr soaddr = reinterpret_cast(addr) - si->base; // Search the library's symbol table for any defined symbol which // contains this address. for (size_t i = 0; i < si->nchain; ++i) { Elf32_Sym* sym = &si->symtab[i]; if (sym->st_shndx != SHN_UNDEF && soaddr >= sym->st_value && soaddr < sym->st_value + sym->st_size) { return sym; } } return NULL; } #if 0 static void dump(soinfo* si) { Elf32_Sym* s = si->symtab; for (unsigned n = 0; n < si->nchain; n++) { TRACE("%04d> %08x: %02x %04x %08x %08x %s", n, s, s->st_info, s->st_shndx, s->st_value, s->st_size, si->strtab + s->st_name); s++; } } #endif static int open_library_on_path(const char* name, const char* const paths[]) { char buf[512]; for (size_t i = 0; paths[i] != NULL; ++i) { int n = __libc_format_buffer(buf, sizeof(buf), "%s/%s", paths[i], name); if (n < 0 || n >= static_cast(sizeof(buf))) { PRINT("Warning: ignoring very long library path: %s/%s", paths[i], name); continue; } int fd = TEMP_FAILURE_RETRY(open(buf, O_RDONLY | O_CLOEXEC)); if (fd != -1) { return fd; } } return -1; } static int open_library(const char* name) { TRACE("[ opening %s ]", name); // If the name contains a slash, we should attempt to open it directly and not search the paths. if (strchr(name, '/') != NULL) { int fd = TEMP_FAILURE_RETRY(open(name, O_RDONLY | O_CLOEXEC)); if (fd != -1) { return fd; } // ...but nvidia binary blobs (at least) rely on this behavior, so fall through for now. } // Otherwise we try LD_LIBRARY_PATH first, and fall back to the built-in well known paths. int fd = open_library_on_path(name, gLdPaths); if (fd == -1) { fd = open_library_on_path(name, gSoPaths); } return fd; } static soinfo* load_library(const char* name) { // Open the file. int fd = open_library(name); if (fd == -1) { DL_ERR("library \"%s\" not found", name); return NULL; } // Read the ELF header and load the segments. ElfReader elf_reader(name, fd); if (!elf_reader.Load()) { return NULL; } const char* bname = strrchr(name, '/'); soinfo* si = soinfo_alloc(bname ? bname + 1 : name); if (si == NULL) { return NULL; } si->base = elf_reader.load_start(); si->size = elf_reader.load_size(); si->load_bias = elf_reader.load_bias(); si->flags = 0; si->entry = 0; si->dynamic = NULL; si->phnum = elf_reader.phdr_count(); si->phdr = elf_reader.loaded_phdr(); return si; } static soinfo *find_loaded_library(const char *name) { soinfo *si; const char *bname; // TODO: don't use basename only for determining libraries // http://code.google.com/p/android/issues/detail?id=6670 bname = strrchr(name, '/'); bname = bname ? bname + 1 : name; for (si = solist; si != NULL; si = si->next) { if (!strcmp(bname, si->name)) { return si; } } return NULL; } static soinfo* find_library_internal(const char* name) { if (name == NULL) { return somain; } soinfo* si = find_loaded_library(name); if (si != NULL) { if (si->flags & FLAG_LINKED) { return si; } DL_ERR("OOPS: recursive link to \"%s\"", si->name); return NULL; } TRACE("[ '%s' has not been loaded yet. Locating...]", name); si = load_library(name); if (si == NULL) { return NULL; } // At this point we know that whatever is loaded @ base is a valid ELF // shared library whose segments are properly mapped in. TRACE("[ init_library base=0x%08x sz=0x%08x name='%s' ]", si->base, si->size, si->name); if (!soinfo_link_image(si)) { munmap(reinterpret_cast(si->base), si->size); soinfo_free(si); return NULL; } return si; } static soinfo* find_library(const char* name) { soinfo* si = find_library_internal(name); if (si != NULL) { si->ref_count++; } return si; } static int soinfo_unload(soinfo* si) { if (si->ref_count == 1) { TRACE("unloading '%s'", si->name); si->CallDestructors(); for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { if (d->d_tag == DT_NEEDED) { const char* library_name = si->strtab + d->d_un.d_val; soinfo* lsi = find_loaded_library(library_name); if (lsi != NULL) { TRACE("%s needs to unload %s", si->name, lsi->name); soinfo_unload(lsi); } else { // TODO: should we return -1 in this case? DL_ERR("\"%s\": could not unload dependent library", si->name); } } } munmap(reinterpret_cast(si->base), si->size); notify_gdb_of_unload(si); soinfo_free(si); si->ref_count = 0; } else { si->ref_count--; TRACE("not unloading '%s', decrementing ref_count to %d", si->name, si->ref_count); } return 0; } void do_android_update_LD_LIBRARY_PATH(const char* ld_library_path) { if (!get_AT_SECURE()) { parse_LD_LIBRARY_PATH(ld_library_path); } } soinfo* do_dlopen(const char* name, int flags) { if ((flags & ~(RTLD_NOW|RTLD_LAZY|RTLD_LOCAL|RTLD_GLOBAL)) != 0) { DL_ERR("invalid flags to dlopen: %x", flags); return NULL; } set_soinfo_pool_protection(PROT_READ | PROT_WRITE); soinfo* si = find_library(name); if (si != NULL) { si->CallConstructors(); } set_soinfo_pool_protection(PROT_READ); return si; } int do_dlclose(soinfo* si) { set_soinfo_pool_protection(PROT_READ | PROT_WRITE); int result = soinfo_unload(si); set_soinfo_pool_protection(PROT_READ); return result; } /* TODO: don't use unsigned for addrs below. It works, but is not * ideal. They should probably be either uint32_t, Elf32_Addr, or unsigned * long. */ static int soinfo_relocate(soinfo* si, Elf32_Rel* rel, unsigned count, soinfo* needed[]) { Elf32_Sym* symtab = si->symtab; const char* strtab = si->strtab; Elf32_Sym* s; Elf32_Rel* start = rel; soinfo* lsi; for (size_t idx = 0; idx < count; ++idx, ++rel) { unsigned type = ELF32_R_TYPE(rel->r_info); unsigned sym = ELF32_R_SYM(rel->r_info); Elf32_Addr reloc = static_cast(rel->r_offset + si->load_bias); Elf32_Addr sym_addr = 0; char* sym_name = NULL; DEBUG("Processing '%s' relocation at index %d", si->name, idx); if (type == 0) { // R_*_NONE continue; } if (sym != 0) { sym_name = (char *)(strtab + symtab[sym].st_name); s = soinfo_do_lookup(si, sym_name, &lsi, needed); if (s == NULL) { /* We only allow an undefined symbol if this is a weak reference.. */ s = &symtab[sym]; if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { DL_ERR("cannot locate symbol \"%s\" referenced by \"%s\"...", sym_name, si->name); return -1; } /* IHI0044C AAELF 4.5.1.1: Libraries are not searched to resolve weak references. It is not an error for a weak reference to remain unsatisfied. During linking, the value of an undefined weak reference is: - Zero if the relocation type is absolute - The address of the place if the relocation is pc-relative - The address of nominal base address if the relocation type is base-relative. */ switch (type) { #if defined(ANDROID_ARM_LINKER) case R_ARM_JUMP_SLOT: case R_ARM_GLOB_DAT: case R_ARM_ABS32: case R_ARM_RELATIVE: /* Don't care. */ #elif defined(ANDROID_X86_LINKER) case R_386_JMP_SLOT: case R_386_GLOB_DAT: case R_386_32: case R_386_RELATIVE: /* Dont' care. */ #endif /* ANDROID_*_LINKER */ /* sym_addr was initialized to be zero above or relocation code below does not care about value of sym_addr. No need to do anything. */ break; #if defined(ANDROID_X86_LINKER) case R_386_PC32: sym_addr = reloc; break; #endif /* ANDROID_X86_LINKER */ #if defined(ANDROID_ARM_LINKER) case R_ARM_COPY: /* Fall through. Can't really copy if weak symbol is not found in run-time. */ #endif /* ANDROID_ARM_LINKER */ default: DL_ERR("unknown weak reloc type %d @ %p (%d)", type, rel, (int) (rel - start)); return -1; } } else { /* We got a definition. */ #if 0 if ((base == 0) && (si->base != 0)) { /* linking from libraries to main image is bad */ DL_ERR("cannot locate \"%s\"...", strtab + symtab[sym].st_name); return -1; } #endif sym_addr = static_cast(s->st_value + lsi->load_bias); } count_relocation(kRelocSymbol); } else { s = NULL; } /* TODO: This is ugly. Split up the relocations by arch into * different files. */ switch(type){ #if defined(ANDROID_ARM_LINKER) case R_ARM_JUMP_SLOT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); *reinterpret_cast(reloc) = sym_addr; break; case R_ARM_GLOB_DAT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); *reinterpret_cast(reloc) = sym_addr; break; case R_ARM_ABS32: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO ABS %08x <- %08x %s", reloc, sym_addr, sym_name); *reinterpret_cast(reloc) += sym_addr; break; case R_ARM_REL32: count_relocation(kRelocRelative); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x - %08x %s", reloc, sym_addr, rel->r_offset, sym_name); *reinterpret_cast(reloc) += sym_addr - rel->r_offset; break; #elif defined(ANDROID_X86_LINKER) case R_386_JMP_SLOT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO JMP_SLOT %08x <- %08x %s", reloc, sym_addr, sym_name); *reinterpret_cast(reloc) = sym_addr; break; case R_386_GLOB_DAT: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO GLOB_DAT %08x <- %08x %s", reloc, sym_addr, sym_name); *reinterpret_cast(reloc) = sym_addr; break; #elif defined(ANDROID_MIPS_LINKER) case R_MIPS_REL32: count_relocation(kRelocAbsolute); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO REL32 %08x <- %08x %s", reloc, sym_addr, (sym_name) ? sym_name : "*SECTIONHDR*"); if (s) { *reinterpret_cast(reloc) += sym_addr; } else { *reinterpret_cast(reloc) += si->base; } break; #endif /* ANDROID_*_LINKER */ #if defined(ANDROID_ARM_LINKER) case R_ARM_RELATIVE: #elif defined(ANDROID_X86_LINKER) case R_386_RELATIVE: #endif /* ANDROID_*_LINKER */ count_relocation(kRelocRelative); MARK(rel->r_offset); if (sym) { DL_ERR("odd RELATIVE form..."); return -1; } TRACE_TYPE(RELO, "RELO RELATIVE %08x <- +%08x", reloc, si->base); *reinterpret_cast(reloc) += si->base; break; #if defined(ANDROID_X86_LINKER) case R_386_32: count_relocation(kRelocRelative); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO R_386_32 %08x <- +%08x %s", reloc, sym_addr, sym_name); *reinterpret_cast(reloc) += sym_addr; break; case R_386_PC32: count_relocation(kRelocRelative); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO R_386_PC32 %08x <- +%08x (%08x - %08x) %s", reloc, (sym_addr - reloc), sym_addr, reloc, sym_name); *reinterpret_cast(reloc) += (sym_addr - reloc); break; #endif /* ANDROID_X86_LINKER */ #ifdef ANDROID_ARM_LINKER case R_ARM_COPY: if ((si->flags & FLAG_EXE) == 0) { /* * http://infocenter.arm.com/help/topic/com.arm.doc.ihi0044d/IHI0044D_aaelf.pdf * * Section 4.7.1.10 "Dynamic relocations" * R_ARM_COPY may only appear in executable objects where e_type is * set to ET_EXEC. * * TODO: FLAG_EXE is set for both ET_DYN and ET_EXEC executables. * We should explicitly disallow ET_DYN executables from having * R_ARM_COPY relocations. */ DL_ERR("%s R_ARM_COPY relocations only supported for ET_EXEC", si->name); return -1; } count_relocation(kRelocCopy); MARK(rel->r_offset); TRACE_TYPE(RELO, "RELO %08x <- %d @ %08x %s", reloc, s->st_size, sym_addr, sym_name); if (reloc == sym_addr) { Elf32_Sym *src = soinfo_do_lookup(NULL, sym_name, &lsi, needed); if (src == NULL) { DL_ERR("%s R_ARM_COPY relocation source cannot be resolved", si->name); return -1; } if (lsi->has_DT_SYMBOLIC) { DL_ERR("%s invalid R_ARM_COPY relocation against DT_SYMBOLIC shared " "library %s (built with -Bsymbolic?)", si->name, lsi->name); return -1; } if (s->st_size < src->st_size) { DL_ERR("%s R_ARM_COPY relocation size mismatch (%d < %d)", si->name, s->st_size, src->st_size); return -1; } memcpy((void*)reloc, (void*)(src->st_value + lsi->load_bias), src->st_size); } else { DL_ERR("%s R_ARM_COPY relocation target cannot be resolved", si->name); return -1; } break; #endif /* ANDROID_ARM_LINKER */ default: DL_ERR("unknown reloc type %d @ %p (%d)", type, rel, (int) (rel - start)); return -1; } } return 0; } #ifdef ANDROID_MIPS_LINKER static int mips_relocate_got(soinfo* si, soinfo* needed[]) { unsigned *got; unsigned local_gotno, gotsym, symtabno; Elf32_Sym *symtab, *sym; unsigned g; got = si->plt_got; local_gotno = si->mips_local_gotno; gotsym = si->mips_gotsym; symtabno = si->mips_symtabno; symtab = si->symtab; /* * got[0] is address of lazy resolver function * got[1] may be used for a GNU extension * set it to a recognizable address in case someone calls it * (should be _rtld_bind_start) * FIXME: maybe this should be in a separate routine */ if ((si->flags & FLAG_LINKER) == 0) { g = 0; got[g++] = 0xdeadbeef; if (got[g] & 0x80000000) { got[g++] = 0xdeadfeed; } /* * Relocate the local GOT entries need to be relocated */ for (; g < local_gotno; g++) { got[g] += si->load_bias; } } /* Now for the global GOT entries */ sym = symtab + gotsym; got = si->plt_got + local_gotno; for (g = gotsym; g < symtabno; g++, sym++, got++) { const char* sym_name; Elf32_Sym* s; soinfo* lsi; /* This is an undefined reference... try to locate it */ sym_name = si->strtab + sym->st_name; s = soinfo_do_lookup(si, sym_name, &lsi, needed); if (s == NULL) { /* We only allow an undefined symbol if this is a weak reference.. */ s = &symtab[g]; if (ELF32_ST_BIND(s->st_info) != STB_WEAK) { DL_ERR("cannot locate \"%s\"...", sym_name); return -1; } *got = 0; } else { /* FIXME: is this sufficient? * For reference see NetBSD link loader * http://cvsweb.netbsd.org/bsdweb.cgi/src/libexec/ld.elf_so/arch/mips/mips_reloc.c?rev=1.53&content-type=text/x-cvsweb-markup */ *got = lsi->load_bias + s->st_value; } } return 0; } #endif /* Please read the "Initialization and Termination functions" functions. * of the linker design note in bionic/linker/README.TXT to understand * what the following code is doing. * * The important things to remember are: * * DT_PREINIT_ARRAY must be called first for executables, and should * not appear in shared libraries. * * DT_INIT should be called before DT_INIT_ARRAY if both are present * * DT_FINI should be called after DT_FINI_ARRAY if both are present * * DT_FINI_ARRAY must be parsed in reverse order. */ void soinfo::CallArray(const char* array_name UNUSED, linker_function_t* functions, size_t count, bool reverse) { if (functions == NULL) { return; } TRACE("[ Calling %s (size %d) @ %p for '%s' ]", array_name, count, functions, name); int begin = reverse ? (count - 1) : 0; int end = reverse ? -1 : count; int step = reverse ? -1 : 1; for (int i = begin; i != end; i += step) { TRACE("[ %s[%d] == %p ]", array_name, i, functions[i]); CallFunction("function", functions[i]); } TRACE("[ Done calling %s for '%s' ]", array_name, name); } void soinfo::CallFunction(const char* function_name UNUSED, linker_function_t function) { if (function == NULL || reinterpret_cast(function) == static_cast(-1)) { return; } TRACE("[ Calling %s @ %p for '%s' ]", function_name, function, name); function(); TRACE("[ Done calling %s @ %p for '%s' ]", function_name, function, name); // The function may have called dlopen(3) or dlclose(3), so we need to ensure our data structures // are still writable. This happens with our debug malloc (see http://b/7941716). set_soinfo_pool_protection(PROT_READ | PROT_WRITE); } void soinfo::CallPreInitConstructors() { CallArray("DT_PREINIT_ARRAY", preinit_array, preinit_array_count, false); } void soinfo::CallConstructors() { if (constructors_called) { return; } // We set constructors_called before actually calling the constructors, otherwise it doesn't // protect against recursive constructor calls. One simple example of constructor recursion // is the libc debug malloc, which is implemented in libc_malloc_debug_leak.so: // 1. The program depends on libc, so libc's constructor is called here. // 2. The libc constructor calls dlopen() to load libc_malloc_debug_leak.so. // 3. dlopen() calls the constructors on the newly created // soinfo for libc_malloc_debug_leak.so. // 4. The debug .so depends on libc, so CallConstructors is // called again with the libc soinfo. If it doesn't trigger the early- // out above, the libc constructor will be called again (recursively!). constructors_called = true; if (!(flags & FLAG_EXE) && preinit_array) { DL_ERR("shared library \"%s\" has a preinit_array table @ %p", name, preinit_array); return; } if (dynamic != NULL) { for (Elf32_Dyn* d = dynamic; d->d_tag != DT_NULL; ++d) { if (d->d_tag == DT_NEEDED) { const char* library_name = strtab + d->d_un.d_val; soinfo* lsi = find_loaded_library(library_name); if (lsi == NULL) { DL_ERR("\"%s\": could not initialize dependent library", name); } else { lsi->CallConstructors(); } } } } CallFunction("DT_INIT", init_func); CallArray("DT_INIT_ARRAY", init_array, init_array_count, false); } void soinfo::CallDestructors() { CallArray("DT_FINI_ARRAY", fini_array, fini_array_count, true); CallFunction("DT_FINI", fini_func); } /* Force any of the closed stdin, stdout and stderr to be associated with /dev/null. */ static int nullify_closed_stdio() { int dev_null, i, status; int return_value = 0; dev_null = TEMP_FAILURE_RETRY(open("/dev/null", O_RDWR)); if (dev_null < 0) { DL_ERR("cannot open /dev/null: %s", strerror(errno)); return -1; } TRACE("[ Opened /dev/null file-descriptor=%d]", dev_null); /* If any of the stdio file descriptors is valid and not associated with /dev/null, dup /dev/null to it. */ for (i = 0; i < 3; i++) { /* If it is /dev/null already, we are done. */ if (i == dev_null) { continue; } TRACE("[ Nullifying stdio file descriptor %d]", i); status = TEMP_FAILURE_RETRY(fcntl(i, F_GETFL)); /* If file is opened, we are good. */ if (status != -1) { continue; } /* The only error we allow is that the file descriptor does not exist, in which case we dup /dev/null to it. */ if (errno != EBADF) { DL_ERR("fcntl failed: %s", strerror(errno)); return_value = -1; continue; } /* Try dupping /dev/null to this stdio file descriptor and repeat if there is a signal. Note that any errors in closing the stdio descriptor are lost. */ status = TEMP_FAILURE_RETRY(dup2(dev_null, i)); if (status < 0) { DL_ERR("dup2 failed: %s", strerror(errno)); return_value = -1; continue; } } /* If /dev/null is not one of the stdio file descriptors, close it. */ if (dev_null > 2) { TRACE("[ Closing /dev/null file-descriptor=%d]", dev_null); status = TEMP_FAILURE_RETRY(close(dev_null)); if (status == -1) { DL_ERR("close failed: %s", strerror(errno)); return_value = -1; } } return return_value; } static bool soinfo_link_image(soinfo* si) { /* "base" might wrap around UINT32_MAX. */ Elf32_Addr base = si->load_bias; const Elf32_Phdr *phdr = si->phdr; int phnum = si->phnum; bool relocating_linker = (si->flags & FLAG_LINKER) != 0; /* We can't debug anything until the linker is relocated */ if (!relocating_linker) { INFO("[ linking %s ]", si->name); DEBUG("si->base = 0x%08x si->flags = 0x%08x", si->base, si->flags); } /* Extract dynamic section */ size_t dynamic_count; Elf32_Word dynamic_flags; phdr_table_get_dynamic_section(phdr, phnum, base, &si->dynamic, &dynamic_count, &dynamic_flags); if (si->dynamic == NULL) { if (!relocating_linker) { DL_ERR("missing PT_DYNAMIC in \"%s\"", si->name); } return false; } else { if (!relocating_linker) { DEBUG("dynamic = %p", si->dynamic); } } #ifdef ANDROID_ARM_LINKER (void) phdr_table_get_arm_exidx(phdr, phnum, base, &si->ARM_exidx, &si->ARM_exidx_count); #endif /* extract useful information from dynamic section */ uint32_t needed_count = 0; for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { DEBUG("d = %p, d[0](tag) = 0x%08x d[1](val) = 0x%08x", d, d->d_tag, d->d_un.d_val); switch(d->d_tag){ case DT_HASH: si->nbucket = ((unsigned *) (base + d->d_un.d_ptr))[0]; si->nchain = ((unsigned *) (base + d->d_un.d_ptr))[1]; si->bucket = (unsigned *) (base + d->d_un.d_ptr + 8); si->chain = (unsigned *) (base + d->d_un.d_ptr + 8 + si->nbucket * 4); break; case DT_STRTAB: si->strtab = (const char *) (base + d->d_un.d_ptr); break; case DT_SYMTAB: si->symtab = (Elf32_Sym *) (base + d->d_un.d_ptr); break; case DT_PLTREL: if (d->d_un.d_val != DT_REL) { DL_ERR("unsupported DT_RELA in \"%s\"", si->name); return false; } break; case DT_JMPREL: si->plt_rel = (Elf32_Rel*) (base + d->d_un.d_ptr); break; case DT_PLTRELSZ: si->plt_rel_count = d->d_un.d_val / sizeof(Elf32_Rel); break; case DT_REL: si->rel = (Elf32_Rel*) (base + d->d_un.d_ptr); break; case DT_RELSZ: si->rel_count = d->d_un.d_val / sizeof(Elf32_Rel); break; case DT_PLTGOT: /* Save this in case we decide to do lazy binding. We don't yet. */ si->plt_got = (unsigned *)(base + d->d_un.d_ptr); break; case DT_DEBUG: // Set the DT_DEBUG entry to the address of _r_debug for GDB // if the dynamic table is writable if ((dynamic_flags & PF_W) != 0) { d->d_un.d_val = (int) &_r_debug; } break; case DT_RELA: DL_ERR("unsupported DT_RELA in \"%s\"", si->name); return false; case DT_INIT: si->init_func = reinterpret_cast(base + d->d_un.d_ptr); DEBUG("%s constructors (init func) found at %p", si->name, si->init_func); break; case DT_FINI: si->fini_func = reinterpret_cast(base + d->d_un.d_ptr); DEBUG("%s destructors (fini func) found at %p", si->name, si->fini_func); break; case DT_INIT_ARRAY: si->init_array = reinterpret_cast(base + d->d_un.d_ptr); DEBUG("%s constructors (init_array) found at %p", si->name, si->init_array); break; case DT_INIT_ARRAYSZ: si->init_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); break; case DT_FINI_ARRAY: si->fini_array = reinterpret_cast(base + d->d_un.d_ptr); DEBUG("%s destructors (fini_array) found at %p", si->name, si->fini_array); break; case DT_FINI_ARRAYSZ: si->fini_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); break; case DT_PREINIT_ARRAY: si->preinit_array = reinterpret_cast(base + d->d_un.d_ptr); DEBUG("%s constructors (preinit_array) found at %p", si->name, si->preinit_array); break; case DT_PREINIT_ARRAYSZ: si->preinit_array_count = ((unsigned)d->d_un.d_val) / sizeof(Elf32_Addr); break; case DT_TEXTREL: si->has_text_relocations = true; break; case DT_SYMBOLIC: si->has_DT_SYMBOLIC = true; break; case DT_NEEDED: ++needed_count; break; #if defined DT_FLAGS // TODO: why is DT_FLAGS not defined? case DT_FLAGS: if (d->d_un.d_val & DF_TEXTREL) { si->has_text_relocations = true; } if (d->d_un.d_val & DF_SYMBOLIC) { si->has_DT_SYMBOLIC = true; } break; #endif #if defined(ANDROID_MIPS_LINKER) case DT_STRSZ: case DT_SYMENT: case DT_RELENT: break; case DT_MIPS_RLD_MAP: // Set the DT_MIPS_RLD_MAP entry to the address of _r_debug for GDB. { r_debug** dp = (r_debug**) d->d_un.d_ptr; *dp = &_r_debug; } break; case DT_MIPS_RLD_VERSION: case DT_MIPS_FLAGS: case DT_MIPS_BASE_ADDRESS: case DT_MIPS_UNREFEXTNO: break; case DT_MIPS_SYMTABNO: si->mips_symtabno = d->d_un.d_val; break; case DT_MIPS_LOCAL_GOTNO: si->mips_local_gotno = d->d_un.d_val; break; case DT_MIPS_GOTSYM: si->mips_gotsym = d->d_un.d_val; break; default: DEBUG("Unused DT entry: type 0x%08x arg 0x%08x", d->d_tag, d->d_un.d_val); break; #endif } } DEBUG("si->base = 0x%08x, si->strtab = %p, si->symtab = %p", si->base, si->strtab, si->symtab); // Sanity checks. if (relocating_linker && needed_count != 0) { DL_ERR("linker cannot have DT_NEEDED dependencies on other libraries"); return false; } if (si->nbucket == 0) { DL_ERR("empty/missing DT_HASH in \"%s\" (built with --hash-style=gnu?)", si->name); return false; } if (si->strtab == 0) { DL_ERR("empty/missing DT_STRTAB in \"%s\"", si->name); return false; } if (si->symtab == 0) { DL_ERR("empty/missing DT_SYMTAB in \"%s\"", si->name); return false; } /* if this is the main executable, then load all of the preloads now */ if (si->flags & FLAG_EXE) { memset(gLdPreloads, 0, sizeof(gLdPreloads)); for (size_t i = 0; gLdPreloadNames[i] != NULL; i++) { soinfo* lsi = find_library(gLdPreloadNames[i]); if (lsi == NULL) { strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", gLdPreloadNames[i], si->name, tmp_err_buf); return false; } gLdPreloads[i] = lsi; } } soinfo** needed = (soinfo**) alloca((1 + needed_count) * sizeof(soinfo*)); soinfo** pneeded = needed; for (Elf32_Dyn* d = si->dynamic; d->d_tag != DT_NULL; ++d) { if (d->d_tag == DT_NEEDED) { const char* library_name = si->strtab + d->d_un.d_val; DEBUG("%s needs %s", si->name, library_name); soinfo* lsi = find_library(library_name); if (lsi == NULL) { strlcpy(tmp_err_buf, linker_get_error_buffer(), sizeof(tmp_err_buf)); DL_ERR("could not load library \"%s\" needed by \"%s\"; caused by %s", library_name, si->name, tmp_err_buf); return false; } *pneeded++ = lsi; } } *pneeded = NULL; if (si->has_text_relocations) { /* Unprotect the segments, i.e. make them writable, to allow * text relocations to work properly. We will later call * phdr_table_protect_segments() after all of them are applied * and all constructors are run. */ if (phdr_table_unprotect_segments(si->phdr, si->phnum, si->load_bias) < 0) { DL_ERR("can't unprotect loadable segments for \"%s\": %s", si->name, strerror(errno)); return false; } } if (si->plt_rel != NULL) { DEBUG("[ relocating %s plt ]", si->name ); if (soinfo_relocate(si, si->plt_rel, si->plt_rel_count, needed)) { return false; } } if (si->rel != NULL) { DEBUG("[ relocating %s ]", si->name ); if (soinfo_relocate(si, si->rel, si->rel_count, needed)) { return false; } } #ifdef ANDROID_MIPS_LINKER if (mips_relocate_got(si, needed)) { return false; } #endif si->flags |= FLAG_LINKED; DEBUG("[ finished linking %s ]", si->name); if (si->has_text_relocations) { /* All relocations are done, we can protect our segments back to * read-only. */ if (phdr_table_protect_segments(si->phdr, si->phnum, si->load_bias) < 0) { DL_ERR("can't protect segments for \"%s\": %s", si->name, strerror(errno)); return false; } } /* We can also turn on GNU RELRO protection */ if (phdr_table_protect_gnu_relro(si->phdr, si->phnum, si->load_bias) < 0) { DL_ERR("can't enable GNU RELRO protection for \"%s\": %s", si->name, strerror(errno)); return false; } // If this is a setuid/setgid program, close the security hole described in // ftp://ftp.freebsd.org/pub/FreeBSD/CERT/advisories/FreeBSD-SA-02:23.stdio.asc if (get_AT_SECURE()) { nullify_closed_stdio(); } notify_gdb_of_load(si); return true; } /* * This code is called after the linker has linked itself and * fixed it's own GOT. It is safe to make references to externs * and other non-local data at this point. */ static Elf32_Addr __linker_init_post_relocation(KernelArgumentBlock& args, Elf32_Addr linker_base) { /* NOTE: we store the args pointer on a special location * of the temporary TLS area in order to pass it to * the C Library's runtime initializer. * * The initializer must clear the slot and reset the TLS * to point to a different location to ensure that no other * shared library constructor can access it. */ __libc_init_tls(args); #if TIMING struct timeval t0, t1; gettimeofday(&t0, 0); #endif // Initialize environment functions, and get to the ELF aux vectors table. linker_env_init(args); debuggerd_init(); // Get a few environment variables. const char* LD_DEBUG = linker_env_get("LD_DEBUG"); if (LD_DEBUG != NULL) { gLdDebugVerbosity = atoi(LD_DEBUG); } // Normally, these are cleaned by linker_env_init, but the test // doesn't cost us anything. const char* ldpath_env = NULL; const char* ldpreload_env = NULL; if (!get_AT_SECURE()) { ldpath_env = linker_env_get("LD_LIBRARY_PATH"); ldpreload_env = linker_env_get("LD_PRELOAD"); } INFO("[ android linker & debugger ]"); soinfo* si = soinfo_alloc(args.argv[0]); if (si == NULL) { exit(EXIT_FAILURE); } /* bootstrap the link map, the main exe always needs to be first */ si->flags |= FLAG_EXE; link_map_t* map = &(si->link_map); map->l_addr = 0; map->l_name = args.argv[0]; map->l_prev = NULL; map->l_next = NULL; _r_debug.r_map = map; r_debug_tail = map; /* gdb expects the linker to be in the debug shared object list. * Without this, gdb has trouble locating the linker's ".text" * and ".plt" sections. Gdb could also potentially use this to * relocate the offset of our exported 'rtld_db_dlactivity' symbol. * Don't use soinfo_alloc(), because the linker shouldn't * be on the soinfo list. */ { static soinfo linker_soinfo; strlcpy(linker_soinfo.name, "/system/bin/linker", sizeof(linker_soinfo.name)); linker_soinfo.flags = 0; linker_soinfo.base = linker_base; /* * Set the dynamic field in the link map otherwise gdb will complain with * the following: * warning: .dynamic section for "/system/bin/linker" is not at the * expected address (wrong library or version mismatch?) */ Elf32_Ehdr *elf_hdr = (Elf32_Ehdr *) linker_base; Elf32_Phdr *phdr = (Elf32_Phdr*)((unsigned char*) linker_base + elf_hdr->e_phoff); phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base, &linker_soinfo.dynamic, NULL, NULL); insert_soinfo_into_debug_map(&linker_soinfo); } // Extract information passed from the kernel. si->phdr = reinterpret_cast(args.getauxval(AT_PHDR)); si->phnum = args.getauxval(AT_PHNUM); si->entry = args.getauxval(AT_ENTRY); /* Compute the value of si->base. We can't rely on the fact that * the first entry is the PHDR because this will not be true * for certain executables (e.g. some in the NDK unit test suite) */ si->base = 0; si->size = phdr_table_get_load_size(si->phdr, si->phnum); si->load_bias = 0; for (size_t i = 0; i < si->phnum; ++i) { if (si->phdr[i].p_type == PT_PHDR) { si->load_bias = reinterpret_cast(si->phdr) - si->phdr[i].p_vaddr; si->base = reinterpret_cast(si->phdr) - si->phdr[i].p_offset; break; } } si->dynamic = NULL; si->ref_count = 1; // Use LD_LIBRARY_PATH and LD_PRELOAD (but only if we aren't setuid/setgid). parse_LD_LIBRARY_PATH(ldpath_env); parse_LD_PRELOAD(ldpreload_env); somain = si; if (!soinfo_link_image(si)) { __libc_format_fd(2, "CANNOT LINK EXECUTABLE: %s\n", linker_get_error_buffer()); exit(EXIT_FAILURE); } si->CallPreInitConstructors(); for (size_t i = 0; gLdPreloads[i] != NULL; ++i) { gLdPreloads[i]->CallConstructors(); } /* After the link_image, the si->load_bias is initialized. * For so lib, the map->l_addr will be updated in notify_gdb_of_load. * We need to update this value for so exe here. So Unwind_Backtrace * for some arch like x86 could work correctly within so exe. */ map->l_addr = si->load_bias; si->CallConstructors(); #if TIMING gettimeofday(&t1,NULL); PRINT("LINKER TIME: %s: %d microseconds", args.argv[0], (int) ( (((long long)t1.tv_sec * 1000000LL) + (long long)t1.tv_usec) - (((long long)t0.tv_sec * 1000000LL) + (long long)t0.tv_usec) )); #endif #if STATS PRINT("RELO STATS: %s: %d abs, %d rel, %d copy, %d symbol", args.argv[0], linker_stats.count[kRelocAbsolute], linker_stats.count[kRelocRelative], linker_stats.count[kRelocCopy], linker_stats.count[kRelocSymbol]); #endif #if COUNT_PAGES { unsigned n; unsigned i; unsigned count = 0; for (n = 0; n < 4096; n++) { if (bitmask[n]) { unsigned x = bitmask[n]; for (i = 0; i < 8; i++) { if (x & 1) { count++; } x >>= 1; } } } PRINT("PAGES MODIFIED: %s: %d (%dKB)", args.argv[0], count, count * 4); } #endif #if TIMING || STATS || COUNT_PAGES fflush(stdout); #endif TRACE("[ Ready to execute '%s' @ 0x%08x ]", si->name, si->entry); return si->entry; } /* Compute the load-bias of an existing executable. This shall only * be used to compute the load bias of an executable or shared library * that was loaded by the kernel itself. * * Input: * elf -> address of ELF header, assumed to be at the start of the file. * Return: * load bias, i.e. add the value of any p_vaddr in the file to get * the corresponding address in memory. */ static Elf32_Addr get_elf_exec_load_bias(const Elf32_Ehdr* elf) { Elf32_Addr offset = elf->e_phoff; const Elf32_Phdr* phdr_table = (const Elf32_Phdr*)((char*)elf + offset); const Elf32_Phdr* phdr_end = phdr_table + elf->e_phnum; for (const Elf32_Phdr* phdr = phdr_table; phdr < phdr_end; phdr++) { if (phdr->p_type == PT_LOAD) { return reinterpret_cast(elf) + phdr->p_offset - phdr->p_vaddr; } } return 0; } /* * This is the entry point for the linker, called from begin.S. This * method is responsible for fixing the linker's own relocations, and * then calling __linker_init_post_relocation(). * * Because this method is called before the linker has fixed it's own * relocations, any attempt to reference an extern variable, extern * function, or other GOT reference will generate a segfault. */ extern "C" Elf32_Addr __linker_init(void* raw_args) { KernelArgumentBlock args(raw_args); Elf32_Addr linker_addr = args.getauxval(AT_BASE); Elf32_Ehdr* elf_hdr = (Elf32_Ehdr*) linker_addr; Elf32_Phdr* phdr = (Elf32_Phdr*)((unsigned char*) linker_addr + elf_hdr->e_phoff); soinfo linker_so; memset(&linker_so, 0, sizeof(soinfo)); linker_so.base = linker_addr; linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); linker_so.dynamic = NULL; linker_so.phdr = phdr; linker_so.phnum = elf_hdr->e_phnum; linker_so.flags |= FLAG_LINKER; if (!soinfo_link_image(&linker_so)) { // It would be nice to print an error message, but if the linker // can't link itself, there's no guarantee that we'll be able to // call write() (because it involves a GOT reference). // // This situation should never occur unless the linker itself // is corrupt. exit(EXIT_FAILURE); } // We have successfully fixed our own relocations. It's safe to run // the main part of the linker now. args.abort_message_ptr = &gAbortMessage; Elf32_Addr start_address = __linker_init_post_relocation(args, linker_addr); set_soinfo_pool_protection(PROT_READ); // Return the address that the calling assembly stub should jump to. return start_address; }