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Fix linker's _r_debug (gdb) info

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* Initialize the exe's l_ld correctly, and initialize its l_addr field
   earlier.

 * Copy the phdr/phnum fields from the linker's temporary soinfo to its
   final soinfo. This change ensures that dl_iterate_phdr shows the phdr
   table for the linker.

 * Change init_linker_info_for_gdb a little: use an soinfo's fields to
   init the soinfo::link_map_head field, then reuse the new
   init_link_map_head function to handle the linker and the executable.

Test: manual
Test: bionic-unit-tests
Bug: https://issuetracker.google.com/112627083
Bug: http://b/110967431
Change-Id: I40fad2c4d48f409347aaa1ccb98d96db89da1dfe
This commit is contained in:
Ryan Prichard 2018-08-20 17:44:42 -07:00
parent 14dd9923b0
commit 0489645e00
4 changed files with 47 additions and 83 deletions
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9
linker/dlfcn.cpp
View file

@ -303,9 +303,7 @@ static uint8_t __libdl_info_buf[sizeof(soinfo)] __attribute__((aligned(8)));
static soinfo* __libdl_info = nullptr; static soinfo* __libdl_info = nullptr;
// This is used by the dynamic linker. Every process gets these symbols for free. // This is used by the dynamic linker. Every process gets these symbols for free.
soinfo* get_libdl_info(const char* linker_path, soinfo* get_libdl_info(const char* linker_path, const soinfo& linker_si) {
const soinfo& linker_si,
const link_map& linker_map) {
CHECK((linker_si.flags_ & FLAG_GNU_HASH) != 0); CHECK((linker_si.flags_ & FLAG_GNU_HASH) != 0);
if (__libdl_info == nullptr) { if (__libdl_info == nullptr) {
@ -314,6 +312,8 @@ soinfo* get_libdl_info(const char* linker_path,
__libdl_info->strtab_ = linker_si.strtab_; __libdl_info->strtab_ = linker_si.strtab_;
__libdl_info->symtab_ = linker_si.symtab_; __libdl_info->symtab_ = linker_si.symtab_;
__libdl_info->load_bias = linker_si.load_bias; __libdl_info->load_bias = linker_si.load_bias;
__libdl_info->phdr = linker_si.phdr;
__libdl_info->phnum = linker_si.phnum;
__libdl_info->gnu_nbucket_ = linker_si.gnu_nbucket_; __libdl_info->gnu_nbucket_ = linker_si.gnu_nbucket_;
__libdl_info->gnu_maskwords_ = linker_si.gnu_maskwords_; __libdl_info->gnu_maskwords_ = linker_si.gnu_maskwords_;
@ -328,9 +328,6 @@ soinfo* get_libdl_info(const char* linker_path,
__libdl_info->soname_ = linker_si.soname_; __libdl_info->soname_ = linker_si.soname_;
__libdl_info->target_sdk_version_ = __ANDROID_API__; __libdl_info->target_sdk_version_ = __ANDROID_API__;
__libdl_info->generate_handle(); __libdl_info->generate_handle();
__libdl_info->link_map_head.l_addr = linker_map.l_addr;
__libdl_info->link_map_head.l_name = linker_map.l_name;
__libdl_info->link_map_head.l_ld = linker_map.l_ld;
#if defined(__work_around_b_24465209__) #if defined(__work_around_b_24465209__)
strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_)); strlcpy(__libdl_info->old_name_, __libdl_info->soname_, sizeof(__libdl_info->old_name_));
#endif #endif

4
linker/linker.h
View file

@ -99,9 +99,7 @@ enum RelocationKind {
void count_relocation(RelocationKind kind); void count_relocation(RelocationKind kind);
soinfo* get_libdl_info(const char* linker_path, soinfo* get_libdl_info(const char* linker_path, const soinfo& linker_si);
const soinfo& linker_si,
const link_map& linker_map);
soinfo* find_containing_library(const void* p); soinfo* find_containing_library(const void* p);

113
linker/linker_main.cpp
View file

@ -67,6 +67,7 @@ static void get_elf_base_from_phdr(const ElfW(Phdr)* phdr_table, size_t phdr_cou
static soinfo* solist; static soinfo* solist;
static soinfo* sonext; static soinfo* sonext;
static soinfo* somain; // main process, always the one after libdl_info static soinfo* somain; // main process, always the one after libdl_info
static soinfo* solinker;
static soinfo* vdso; // vdso if present static soinfo* vdso; // vdso if present
void solist_add_soinfo(soinfo* si) { void solist_add_soinfo(soinfo* si) {
@ -170,29 +171,13 @@ static void add_vdso(KernelArgumentBlock& args) {
vdso = si; vdso = si;
} }
/* gdb expects the linker to be in the debug shared object list. // Initializes an soinfo's link_map_head field using other fields from the
* Without this, gdb has trouble locating the linker's ".text" // soinfo (phdr, phnum, load_bias).
* and ".plt" sections. Gdb could also potentially use this to static void init_link_map_head(soinfo& info, const char* linker_path) {
* relocate the offset of our exported 'rtld_db_dlactivity' symbol. auto& map = info.link_map_head;
* Note that the linker shouldn't be on the soinfo list. map.l_addr = info.load_bias;
*/ map.l_name = const_cast<char*>(linker_path);
static link_map linker_link_map; phdr_table_get_dynamic_section(info.phdr, info.phnum, info.load_bias, &map.l_ld, nullptr);
static void init_linker_info_for_gdb(ElfW(Addr) linker_base, char* linker_path) {
linker_link_map.l_addr = linker_base;
linker_link_map.l_name = linker_path;
/*
* 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.l_ld, nullptr);
} }
extern "C" int __system_properties_init(void); extern "C" int __system_properties_init(void);
@ -303,32 +288,32 @@ static ElfW(Addr) linker_main(KernelArgumentBlock& args) {
stat("/init", &file_stat); stat("/init", &file_stat);
} }
// Initialize the main exe's soinfo.
const char* executable_path = get_executable_path(); const char* executable_path = get_executable_path();
soinfo* si = soinfo_alloc(&g_default_namespace, executable_path, &file_stat, 0, RTLD_GLOBAL); soinfo* si = soinfo_alloc(&g_default_namespace, executable_path, &file_stat, 0, RTLD_GLOBAL);
somain = si;
// Bootstrap the link map, the main exe always needs to be first. si->phdr = reinterpret_cast<ElfW(Phdr)*>(args.getauxval(AT_PHDR));
si->phnum = args.getauxval(AT_PHNUM);
get_elf_base_from_phdr(si->phdr, si->phnum, &si->base, &si->load_bias);
si->size = phdr_table_get_load_size(si->phdr, si->phnum);
si->dynamic = nullptr;
si->set_main_executable(); si->set_main_executable();
link_map* map = &(si->link_map_head); init_link_map_head(*si, executable_path);
// Register the main executable and the linker upfront to have // Register the main executable and the linker upfront to have
// gdb aware of them before loading the rest of the dependency // gdb aware of them before loading the rest of the dependency
// tree. // tree.
map->l_addr = 0; //
map->l_name = const_cast<char*>(executable_path); // gdb expects the linker to be in the debug shared object list.
insert_link_map_into_debug_map(map); // Without this, gdb has trouble locating the linker's ".text"
insert_link_map_into_debug_map(&linker_link_map); // and ".plt" sections. Gdb could also potentially use this to
// relocate the offset of our exported 'rtld_db_dlactivity' symbol.
//
insert_link_map_into_debug_map(&si->link_map_head);
insert_link_map_into_debug_map(&solinker->link_map_head);
add_vdso(args); add_vdso(args);
// Extract information passed from the kernel.
si->phdr = reinterpret_cast<ElfW(Phdr)*>(args.getauxval(AT_PHDR));
si->phnum = args.getauxval(AT_PHNUM);
get_elf_base_from_phdr(si->phdr, si->phnum, &si->base, &si->load_bias);
si->size = phdr_table_get_load_size(si->phdr, si->phnum);
si->dynamic = nullptr;
ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(si->base); ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(si->base);
// We haven't supported non-PIE since Lollipop for security reasons. // We haven't supported non-PIE since Lollipop for security reasons.
@ -351,8 +336,6 @@ static ElfW(Addr) linker_main(KernelArgumentBlock& args) {
parse_LD_LIBRARY_PATH(ldpath_env); parse_LD_LIBRARY_PATH(ldpath_env);
parse_LD_PRELOAD(ldpreload_env); parse_LD_PRELOAD(ldpreload_env);
somain = si;
std::vector<android_namespace_t*> namespaces = init_default_namespaces(executable_path); std::vector<android_namespace_t*> namespaces = init_default_namespaces(executable_path);
if (!si->prelink_image()) __linker_cannot_link(g_argv[0]); if (!si->prelink_image()) __linker_cannot_link(g_argv[0]);
@ -411,13 +394,6 @@ static ElfW(Addr) linker_main(KernelArgumentBlock& args) {
__get_tls()[TLS_SLOT_BIONIC_PREINIT] = &args; __get_tls()[TLS_SLOT_BIONIC_PREINIT] = &args;
si->call_pre_init_constructors(); 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(); si->call_constructors();
#if TIMING #if TIMING
@ -508,9 +484,7 @@ static void get_elf_base_from_phdr(const ElfW(Phdr)* phdr_table, size_t phdr_cou
} }
static ElfW(Addr) __attribute__((noinline)) static ElfW(Addr) __attribute__((noinline))
__linker_init_post_relocation(KernelArgumentBlock& args, __linker_init_post_relocation(KernelArgumentBlock& args, soinfo& linker_so);
ElfW(Addr) linker_addr,
soinfo& linker_so);
/* /*
* This is the entry point for the linker, called from begin.S. This * This is the entry point for the linker, called from begin.S. This
@ -543,18 +517,18 @@ extern "C" ElfW(Addr) __linker_init(void* raw_args) {
ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_addr); ElfW(Ehdr)* elf_hdr = reinterpret_cast<ElfW(Ehdr)*>(linker_addr);
ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_addr + elf_hdr->e_phoff); ElfW(Phdr)* phdr = reinterpret_cast<ElfW(Phdr)*>(linker_addr + elf_hdr->e_phoff);
soinfo linker_so(nullptr, nullptr, nullptr, 0, 0); soinfo tmp_linker_so(nullptr, nullptr, nullptr, 0, 0);
linker_so.base = linker_addr; tmp_linker_so.base = linker_addr;
linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum); tmp_linker_so.size = phdr_table_get_load_size(phdr, elf_hdr->e_phnum);
linker_so.load_bias = get_elf_exec_load_bias(elf_hdr); tmp_linker_so.load_bias = get_elf_exec_load_bias(elf_hdr);
linker_so.dynamic = nullptr; tmp_linker_so.dynamic = nullptr;
linker_so.phdr = phdr; tmp_linker_so.phdr = phdr;
linker_so.phnum = elf_hdr->e_phnum; tmp_linker_so.phnum = elf_hdr->e_phnum;
linker_so.set_linker_flag(); tmp_linker_so.set_linker_flag();
// Prelink the linker so we can access linker globals. // Prelink the linker so we can access linker globals.
if (!linker_so.prelink_image()) __linker_cannot_link(args.argv[0]); if (!tmp_linker_so.prelink_image()) __linker_cannot_link(args.argv[0]);
// This might not be obvious... The reasons why we pass g_empty_list // 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 // in place of local_group here are (1) we do not really need it, because
@ -562,9 +536,9 @@ extern "C" ElfW(Addr) __linker_init(void* raw_args) {
// itself without having to look into local_group and (2) allocators // itself without having to look into local_group and (2) allocators
// are not yet initialized, and therefore we cannot use linked_list.push_* // are not yet initialized, and therefore we cannot use linked_list.push_*
// functions at this point. // functions at this point.
if (!linker_so.link_image(g_empty_list, g_empty_list, nullptr)) __linker_cannot_link(args.argv[0]); if (!tmp_linker_so.link_image(g_empty_list, g_empty_list, nullptr)) __linker_cannot_link(args.argv[0]);
return __linker_init_post_relocation(args, linker_addr, linker_so); return __linker_init_post_relocation(args, tmp_linker_so);
} }
/* /*
@ -574,15 +548,13 @@ extern "C" ElfW(Addr) __linker_init(void* raw_args) {
* function, so avoid inlining this function (http://b/80503879). * function, so avoid inlining this function (http://b/80503879).
*/ */
static ElfW(Addr) __attribute__((noinline)) static ElfW(Addr) __attribute__((noinline))
__linker_init_post_relocation(KernelArgumentBlock& args, __linker_init_post_relocation(KernelArgumentBlock& args, soinfo& tmp_linker_so) {
ElfW(Addr) linker_addr,
soinfo& linker_so) {
// Initialize the main thread (including TLS, so system calls really work). // Initialize the main thread (including TLS, so system calls really work).
__libc_init_main_thread(args); __libc_init_main_thread(args);
// We didn't protect the linker's RELRO pages in link_image because we // 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... // 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]); if (!tmp_linker_so.protect_relro()) __linker_cannot_link(args.argv[0]);
// Initialize the linker/libc.so shared global inside the linker. // Initialize the linker/libc.so shared global inside the linker.
static libc_shared_globals shared_globals; static libc_shared_globals shared_globals;
@ -599,7 +571,7 @@ __linker_init_post_relocation(KernelArgumentBlock& args,
g_envp = args.envp; g_envp = args.envp;
// Initialize the linker's own global variables // Initialize the linker's own global variables
linker_so.call_constructors(); tmp_linker_so.call_constructors();
// If the linker is not acting as PT_INTERP entry_point is equal to // 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 // _start. Which means that the linker is running as an executable and
@ -615,13 +587,12 @@ __linker_init_post_relocation(KernelArgumentBlock& args,
exit(0); exit(0);
} }
init_linker_info_for_gdb(linker_addr, kLinkerPath);
// Initialize static variables. Note that in order to // Initialize static variables. Note that in order to
// get correct libdl_info we need to call constructors // get correct libdl_info we need to call constructors
// before get_libdl_info(). // before get_libdl_info().
sonext = solist = get_libdl_info(kLinkerPath, linker_so, linker_link_map); sonext = solist = solinker = get_libdl_info(kLinkerPath, tmp_linker_so);
g_default_namespace.add_soinfo(solist); g_default_namespace.add_soinfo(solinker);
init_link_map_head(*solinker, kLinkerPath);
args.abort_message_ptr = &g_abort_message; args.abort_message_ptr = &g_abort_message;
ElfW(Addr) start_address = linker_main(args); ElfW(Addr) start_address = linker_main(args);

4
linker/linker_soinfo.h
View file

@ -361,9 +361,7 @@ struct soinfo {
android_namespace_list_t secondary_namespaces_; android_namespace_list_t secondary_namespaces_;
uintptr_t handle_; uintptr_t handle_;
friend soinfo* get_libdl_info(const char* linker_path, friend soinfo* get_libdl_info(const char* linker_path, const soinfo& linker_si);
const soinfo& linker_si,
const link_map& linker_map);
// version >= 4 // version >= 4
ElfW(Relr)* relr_; ElfW(Relr)* relr_;