linker: Refactoring step 3 of many
Extract linker executable specific code to linker_main.cpp;
this part of code does not have a place in libdl.a/so.
Bug: http://b/14998480
Bug: http://b/30706810
Test: mm && run bionic-unit-tests
Change-Id: I90f7475e93a919b0f9525da22928089ad35b8f6c
diff --git a/linker/linker_main.cpp b/linker/linker_main.cpp
new file mode 100644
index 0000000..2e98bf0
--- /dev/null
+++ b/linker/linker_main.cpp
@@ -0,0 +1,536 @@
+/*
+ * Copyright (C) 2016 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 "linker_main.h"
+
+#include "linker_debug.h"
+#include "linker_gdb_support.h"
+#include "linker_globals.h"
+#include "linker_phdr.h"
+#include "linker_utils.h"
+
+#include "private/bionic_globals.h"
+#include "private/bionic_tls.h"
+#include "private/KernelArgumentBlock.h"
+
+#include "android-base/strings.h"
+#include "android-base/stringprintf.h"
+#include "debuggerd/client.h"
+
+#include <vector>
+
+extern void __libc_init_globals(KernelArgumentBlock&);
+extern void __libc_init_AT_SECURE(KernelArgumentBlock&);
+
+extern "C" void _start();
+
+static ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf);
+
+// These should be preserved static to avoid emitting
+// RELATIVE relocations for the part of the code running
+// before linker links itself.
+
+// TODO (dimtiry): remove somain, rename solist to solist_head
+static soinfo* solist;
+static soinfo* sonext;
+static soinfo* somain; // main process, always the one after libdl_info
+
+void solist_add_soinfo(soinfo* si) {
+ sonext->next = si;
+ sonext = si;
+}
+
+bool solist_remove_soinfo(soinfo* si) {
+ soinfo *prev = nullptr, *trav;
+ for (trav = solist; trav != nullptr; trav = trav->next) {
+ if (trav == si) {
+ break;
+ }
+ prev = trav;
+ }
+
+ if (trav == nullptr) {
+ // si was not in solist
+ PRINT("name \"%s\"@%p is not in solist!", si->get_realpath(), si);
+ return false;
+ }
+
+ // 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;
+ }
+
+ return true;
+}
+
+soinfo* solist_get_head() {
+ return solist;
+}
+
+soinfo* solist_get_somain() {
+ return somain;
+}
+
+int g_ld_debug_verbosity;
+abort_msg_t* g_abort_message = nullptr; // For debuggerd.
+
+static std::vector<std::string> g_ld_preload_names;
+
+static std::vector<soinfo*> g_ld_preloads;
+
+static void parse_path(const char* path, const char* delimiters,
+ std::vector<std::string>* resolved_paths) {
+ std::vector<std::string> paths;
+ split_path(path, delimiters, &paths);
+ resolve_paths(paths, resolved_paths);
+}
+
+static void parse_LD_LIBRARY_PATH(const char* path) {
+ std::vector<std::string> ld_libary_paths;
+ parse_path(path, ":", &ld_libary_paths);
+ g_default_namespace.set_ld_library_paths(std::move(ld_libary_paths));
+}
+
+static void parse_LD_PRELOAD(const char* path) {
+ g_ld_preload_names.clear();
+ if (path != nullptr) {
+ // We have historically supported ':' as well as ' ' in LD_PRELOAD.
+ g_ld_preload_names = android::base::Split(path, " :");
+ std::remove_if(g_ld_preload_names.begin(),
+ g_ld_preload_names.end(),
+ [] (const std::string& s) { return s.empty(); });
+ }
+}
+
+// An empty list of soinfos
+static soinfo_list_t g_empty_list;
+
+static void add_vdso(KernelArgumentBlock& args __unused) {
+#if defined(AT_SYSINFO_EHDR)
+ ElfW(Ehdr)* ehdr_vdso = reinterpret_cast<ElfW(Ehdr)*>(args.getauxval(AT_SYSINFO_EHDR));
+ if (ehdr_vdso == nullptr) {
+ return;
+ }
+
+ soinfo* si = soinfo_alloc(&g_default_namespace, "[vdso]", nullptr, 0, 0);
+
+ si->phdr = reinterpret_cast<ElfW(Phdr)*>(reinterpret_cast<char*>(ehdr_vdso) + ehdr_vdso->e_phoff);
+ si->phnum = ehdr_vdso->e_phnum;
+ si->base = reinterpret_cast<ElfW(Addr)>(ehdr_vdso);
+ si->size = phdr_table_get_load_size(si->phdr, si->phnum);
+ si->load_bias = get_elf_exec_load_bias(ehdr_vdso);
+
+ si->prelink_image();
+ si->link_image(g_empty_list, soinfo_list_t::make_list(si), nullptr);
+#endif
+}
+
+/* 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.
+ * Note that the linker shouldn't be on the soinfo list.
+ */
+static void init_linker_info_for_gdb(ElfW(Addr) linker_base) {
+ static link_map linker_link_map_for_gdb;
+#if defined(__LP64__)
+ static char kLinkerPath[] = "/system/bin/linker64";
+#else
+ static char kLinkerPath[] = "/system/bin/linker";
+#endif
+
+ linker_link_map_for_gdb.l_addr = linker_base;
+ linker_link_map_for_gdb.l_name = kLinkerPath;
+
+ /*
+ * 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?)
+ */
+ ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_base);
+ ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_base + elf_hdr->e_phoff);
+ phdr_table_get_dynamic_section(phdr, elf_hdr->e_phnum, linker_base,
+ &linker_link_map_for_gdb.l_ld, nullptr);
+
+ insert_link_map_into_debug_map(&linker_link_map_for_gdb);
+}
+
+extern "C" int __system_properties_init(void);
+
+static const char* get_executable_path() {
+ static std::string executable_path;
+ if (executable_path.empty()) {
+ char path[PATH_MAX];
+ ssize_t path_len = readlink("/proc/self/exe", path, sizeof(path));
+ if (path_len == -1 || path_len >= static_cast<ssize_t>(sizeof(path))) {
+ __libc_fatal("readlink('/proc/self/exe') failed: %s", strerror(errno));
+ }
+ executable_path = std::string(path, path_len);
+ }
+
+ return executable_path.c_str();
+}
+
+/*
+ * 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 ElfW(Addr) __linker_init_post_relocation(KernelArgumentBlock& args, ElfW(Addr) linker_base) {
+#if TIMING
+ struct timeval t0, t1;
+ gettimeofday(&t0, 0);
+#endif
+
+ // Sanitize the environment.
+ __libc_init_AT_SECURE(args);
+
+ // Initialize system properties
+ __system_properties_init(); // may use 'environ'
+
+ // Register the debuggerd signal handler.
+ debuggerd_callbacks_t callbacks = {
+ .get_abort_message = []() {
+ return g_abort_message;
+ },
+ .post_dump = ¬ify_gdb_of_libraries,
+ };
+ debuggerd_init(&callbacks);
+
+ g_linker_logger.ResetState();
+
+ // Get a few environment variables.
+ const char* LD_DEBUG = getenv("LD_DEBUG");
+ if (LD_DEBUG != nullptr) {
+ g_ld_debug_verbosity = atoi(LD_DEBUG);
+ }
+
+#if defined(__LP64__)
+ INFO("[ Android dynamic linker (64-bit) ]");
+#else
+ INFO("[ Android dynamic linker (32-bit) ]");
+#endif
+
+ // These should have been sanitized by __libc_init_AT_SECURE, but the test
+ // doesn't cost us anything.
+ const char* ldpath_env = nullptr;
+ const char* ldpreload_env = nullptr;
+ if (!getauxval(AT_SECURE)) {
+ ldpath_env = getenv("LD_LIBRARY_PATH");
+ if (ldpath_env != nullptr) {
+ INFO("[ LD_LIBRARY_PATH set to \"%s\" ]", ldpath_env);
+ }
+ ldpreload_env = getenv("LD_PRELOAD");
+ if (ldpreload_env != nullptr) {
+ INFO("[ LD_PRELOAD set to \"%s\" ]", ldpreload_env);
+ }
+ }
+
+ struct stat file_stat;
+ // Stat "/proc/self/exe" instead of executable_path because
+ // the executable could be unlinked by this point and it should
+ // not cause a crash (see http://b/31084669)
+ if (TEMP_FAILURE_RETRY(stat("/proc/self/exe", &file_stat)) != 0) {
+ __libc_fatal("unable to stat \"/proc/self/exe\": %s", strerror(errno));
+ }
+
+ const char* executable_path = get_executable_path();
+ soinfo* si = soinfo_alloc(&g_default_namespace, executable_path, &file_stat, 0, RTLD_GLOBAL);
+ if (si == nullptr) {
+ __libc_fatal("Couldn't allocate soinfo: out of memory?");
+ }
+
+ /* bootstrap the link map, the main exe always needs to be first */
+ si->set_main_executable();
+ link_map* map = &(si->link_map_head);
+
+ // Register the main executable and the linker upfront to have
+ // gdb aware of them before loading the rest of the dependency
+ // tree.
+ map->l_addr = 0;
+ map->l_name = const_cast<char*>(executable_path);
+ insert_link_map_into_debug_map(map);
+ init_linker_info_for_gdb(linker_base);
+
+ // Extract information passed from the kernel.
+ si->phdr = reinterpret_cast<ElfW(Phdr)*>(args.getauxval(AT_PHDR));
+ si->phnum = args.getauxval(AT_PHNUM);
+
+ /* 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<ElfW(Addr)>(si->phdr) - si->phdr[i].p_vaddr;
+ si->base = reinterpret_cast<ElfW(Addr)>(si->phdr) - si->phdr[i].p_offset;
+ break;
+ }
+ }
+ si->dynamic = nullptr;
+
+ ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(si->base);
+ if (elf_hdr->e_type != ET_DYN) {
+ __libc_fatal("\"%s\": error: only position independent executables (PIE) are supported.",
+ g_argv[0]);
+ }
+
+ // 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;
+
+ init_default_namespace();
+
+ if (!si->prelink_image()) {
+ __libc_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", g_argv[0], linker_get_error_buffer());
+ }
+
+ // add somain to global group
+ si->set_dt_flags_1(si->get_dt_flags_1() | DF_1_GLOBAL);
+
+ // Load ld_preloads and dependencies.
+ std::vector<const char*> needed_library_name_list;
+ size_t ld_preloads_count = 0;
+
+ for (const auto& ld_preload_name : g_ld_preload_names) {
+ needed_library_name_list.push_back(ld_preload_name.c_str());
+ ++ld_preloads_count;
+ }
+
+ for_each_dt_needed(si, [&](const char* name) {
+ needed_library_name_list.push_back(name);
+ });
+
+ const char** needed_library_names = &needed_library_name_list[0];
+ size_t needed_libraries_count = needed_library_name_list.size();
+
+ if (needed_libraries_count > 0 &&
+ !find_libraries(&g_default_namespace, si, needed_library_names, needed_libraries_count,
+ nullptr, &g_ld_preloads, ld_preloads_count, RTLD_GLOBAL, nullptr,
+ /* add_as_children */ true)) {
+ __libc_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", g_argv[0], linker_get_error_buffer());
+ } else if (needed_libraries_count == 0) {
+ if (!si->link_image(g_empty_list, soinfo_list_t::make_list(si), nullptr)) {
+ __libc_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", g_argv[0], linker_get_error_buffer());
+ }
+ si->increment_ref_count();
+ }
+
+ add_vdso(args);
+
+ {
+ ProtectedDataGuard guard;
+
+ si->call_pre_init_constructors();
+
+ /* After the prelink_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->call_constructors();
+ }
+
+#if TIMING
+ gettimeofday(&t1, nullptr);
+ PRINT("LINKER TIME: %s: %d microseconds", g_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", g_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];
+#if defined(__LP64__)
+ for (i = 0; i < 32; i++) {
+#else
+ for (i = 0; i < 8; i++) {
+#endif
+ if (x & 1) {
+ count++;
+ }
+ x >>= 1;
+ }
+ }
+ }
+ PRINT("PAGES MODIFIED: %s: %d (%dKB)", g_argv[0], count, count * 4);
+ }
+#endif
+
+#if TIMING || STATS || COUNT_PAGES
+ fflush(stdout);
+#endif
+
+ ElfW(Addr) entry = args.getauxval(AT_ENTRY);
+ TRACE("[ Ready to execute \"%s\" @ %p ]", si->get_realpath(), reinterpret_cast<void*>(entry));
+ return 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 ElfW(Addr) get_elf_exec_load_bias(const ElfW(Ehdr)* elf) {
+ ElfW(Addr) offset = elf->e_phoff;
+ const ElfW(Phdr)* phdr_table =
+ reinterpret_cast<const ElfW(Phdr)*>(reinterpret_cast<uintptr_t>(elf) + offset);
+ const ElfW(Phdr)* phdr_end = phdr_table + elf->e_phnum;
+
+ for (const ElfW(Phdr)* phdr = phdr_table; phdr < phdr_end; phdr++) {
+ if (phdr->p_type == PT_LOAD) {
+ return reinterpret_cast<ElfW(Addr)>(elf) + phdr->p_offset - phdr->p_vaddr;
+ }
+ }
+ return 0;
+}
+
+static void __linker_cannot_link(const char* argv0) {
+ __libc_fatal("CANNOT LINK EXECUTABLE \"%s\": %s", argv0, linker_get_error_buffer());
+}
+
+/*
+ * 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" ElfW(Addr) __linker_init(void* raw_args) {
+ KernelArgumentBlock args(raw_args);
+
+ ElfW(Addr) linker_addr = args.getauxval(AT_BASE);
+ ElfW(Addr) entry_point = args.getauxval(AT_ENTRY);
+ ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_addr);
+ ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_addr + elf_hdr->e_phoff);
+
+ soinfo linker_so(nullptr, nullptr, nullptr, 0, 0);
+
+ // If the linker is not acting as PT_INTERP entry_point is equal to
+ // _start. Which means that the linker is running as an executable and
+ // already linked by PT_INTERP.
+ //
+ // This happens when user tries to run 'adb shell /system/bin/linker'
+ // see also https://code.google.com/p/android/issues/detail?id=63174
+ if (reinterpret_cast<ElfW(Addr)>(&_start) == entry_point) {
+ __libc_format_fd(STDOUT_FILENO,
+ "This is %s, the helper program for shared library executables.\n",
+ args.argv[0]);
+ exit(0);
+ }
+
+ 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 = nullptr;
+ linker_so.phdr = phdr;
+ linker_so.phnum = elf_hdr->e_phnum;
+ linker_so.set_linker_flag();
+
+ // Prelink the linker so we can access linker globals.
+ if (!linker_so.prelink_image()) __linker_cannot_link(args.argv[0]);
+
+ // This might not be obvious... The reasons why we pass g_empty_list
+ // in place of local_group here are (1) we do not really need it, because
+ // linker is built with DT_SYMBOLIC and therefore relocates its symbols against
+ // itself without having to look into local_group and (2) allocators
+ // are not yet initialized, and therefore we cannot use linked_list.push_*
+ // functions at this point.
+ if (!linker_so.link_image(g_empty_list, g_empty_list, nullptr)) __linker_cannot_link(args.argv[0]);
+
+#if defined(__i386__)
+ // On x86, we can't make system calls before this point.
+ // We can't move this up because this needs to assign to a global.
+ // Note that until we call __libc_init_main_thread below we have
+ // no TLS, so you shouldn't make a system call that can fail, because
+ // it will SEGV when it tries to set errno.
+ __libc_init_sysinfo(args);
+#endif
+
+ // Initialize the main thread (including TLS, so system calls really work).
+ __libc_init_main_thread(args);
+
+ // We didn't protect the linker's RELRO pages in link_image because we
+ // couldn't make system calls on x86 at that point, but we can now...
+ if (!linker_so.protect_relro()) __linker_cannot_link(args.argv[0]);
+
+ // Initialize the linker's static libc's globals
+ __libc_init_globals(args);
+
+ // store argc/argv/envp to use them for calling constructors
+ g_argc = args.argc;
+ g_argv = args.argv;
+ g_envp = args.envp;
+
+ // Initialize the linker's own global variables
+ linker_so.call_constructors();
+
+ // Initialize static variables. Note that in order to
+ // get correct libdl_info we need to call constructors
+ // before get_libdl_info().
+ solist = get_libdl_info();
+ sonext = get_libdl_info();
+ g_default_namespace.add_soinfo(get_libdl_info());
+
+ // We have successfully fixed our own relocations. It's safe to run
+ // the main part of the linker now.
+ args.abort_message_ptr = &g_abort_message;
+ ElfW(Addr) start_address = __linker_init_post_relocation(args, linker_addr);
+
+ INFO("[ Jumping to _start (%p)... ]", reinterpret_cast<void*>(start_address));
+
+ // Return the address that the calling assembly stub should jump to.
+ return start_address;
+}