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Loader.so+LibELF: Move most of Loader.so's logic into ELF::DynamicLinker

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Loader.so now just performs the initial self relocations and static
LibC initialisation before handing over to ELF::DynamicLinker::linker_main
to handle the rest of the process.

As a trade-off, ELF::DynamicLinker needs to be explicitly excluded from
Lagom unless we really want to try writing a cross platform dynamic loader
This commit is contained in:
William Marlow 2021-01-01 23:54:43 +00:00 • committed by Andreas Kling
parent 4d32121293
commit 3e815ad5b1
8 changed files with 327 additions and 220 deletions
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230
Userland/DynamicLoader/main.cpp
View file

@ -35,6 +35,7 @@
#include <LibC/unistd.h>
#include <LibCore/File.h>
#include <LibELF/AuxiliaryVector.h>
#include <LibELF/DynamicLinker.h>
#include <LibELF/DynamicLoader.h>
#include <LibELF/DynamicObject.h>
#include <LibELF/Image.h>
@ -57,23 +58,14 @@
char* __static_environ[] = { nullptr }; // We don't get the environment without some libc workarounds..
static HashMap<String, NonnullRefPtr<ELF::DynamicLoader>> g_loaders;
static HashMap<String, NonnullRefPtr<ELF::DynamicObject>> g_loaded_objects;
using MainFunction = int (*)(int, char**, char**);
using LibCExitFunction = void (*)(int);
static size_t g_current_tls_offset = 0;
static size_t g_total_tls_size = 0;
static char** g_envp = nullptr;
static LibCExitFunction g_libc_exit = nullptr;
static void init_libc()
{
environ = __static_environ;
__environ_is_malloced = false;
__stdio_is_initialized = false;
__malloc_init();
// Initialise the copy of libc included statically in Loader.so,
// initialisation of the dynamic libc.so is done by the DynamicLinker
__libc_init();
}
static void perform_self_relocations(auxv_t* auxvp)
@ -112,144 +104,6 @@ static void perform_self_relocations(auxv_t* auxvp)
});
}
static ELF::DynamicObject::SymbolLookupResult global_symbol_lookup(const char* symbol_name)
{
VERBOSE("global symbol lookup: %s\n", symbol_name);
for (auto& lib : g_loaded_objects) {
VERBOSE("looking up in object: %s\n", lib.key.characters());
auto res = lib.value->lookup_symbol(symbol_name);
if (!res.has_value())
continue;
return res.value();
}
// ASSERT_NOT_REACHED();
return {};
}
static void map_library(const String& name, int fd)
{
struct stat lib_stat;
int rc = fstat(fd, &lib_stat);
ASSERT(!rc);
auto loader = ELF::DynamicLoader::construct(name.characters(), fd, lib_stat.st_size);
loader->set_tls_offset(g_current_tls_offset);
loader->set_global_symbol_lookup_function(global_symbol_lookup);
g_loaders.set(name, loader);
g_current_tls_offset += loader->tls_size();
}
static void map_library(const String& name)
{
// TODO: Do we want to also look for libs in other paths too?
String path = String::format("/usr/lib/%s", name.characters());
int fd = open(path.characters(), O_RDONLY);
ASSERT(fd >= 0);
map_library(name, fd);
}
static String get_library_name(const StringView& path)
{
return LexicalPath(path).basename();
}
static Vector<String> get_dependencies(const String& name)
{
auto lib = g_loaders.get(name).value();
Vector<String> dependencies;
lib->for_each_needed_library([&dependencies, &name](auto needed_name) {
if (name == needed_name)
return IterationDecision::Continue;
dependencies.append(needed_name);
return IterationDecision::Continue;
});
return dependencies;
}
static void map_dependencies(const String& name)
{
VERBOSE("mapping dependencies for: %s\n", name.characters());
for (const auto& needed_name : get_dependencies(name)) {
VERBOSE("needed library: %s\n", needed_name.characters());
String library_name = get_library_name(needed_name);
if (!g_loaders.contains(library_name)) {
map_library(library_name);
map_dependencies(library_name);
}
}
}
static void allocate_tls()
{
size_t total_tls_size = 0;
for (const auto& data : g_loaders) {
VERBOSE("%s: TLS Size: %zu\n", data.key.characters(), data.value->tls_size());
total_tls_size += data.value->tls_size();
}
if (total_tls_size) {
[[maybe_unused]] void* tls_address = allocate_tls(total_tls_size);
VERBOSE("from userspace, tls_address: %p\n", tls_address);
}
g_total_tls_size = total_tls_size;
}
static void initialize_libc()
{
// Traditionally, `_start` of the main program initializes libc.
// However, since some libs use malloc() and getenv() in global constructors,
// we have to initialize libc just after it is loaded.
// Also, we can't just mark `__libc_init` with "__attribute__((constructor))"
// because it uses getenv() internally, so `environ` has to be initialized before we call `__libc_init`.
auto res = global_symbol_lookup("environ");
*((char***)res.address) = g_envp;
ASSERT(res.found);
res = global_symbol_lookup("__environ_is_malloced");
ASSERT(res.found);
*((bool*)res.address) = false;
res = global_symbol_lookup("exit");
ASSERT(res.found);
g_libc_exit = (LibCExitFunction)res.address;
res = global_symbol_lookup("__libc_init");
ASSERT(res.found);
typedef void libc_init_func();
((libc_init_func*)res.address)();
}
static void load_elf(const String& name)
{
VERBOSE("load_elf: %s\n", name.characters());
auto loader = g_loaders.get(name).value();
VERBOSE("a1\n");
for (const auto& needed_name : get_dependencies(name)) {
VERBOSE("needed library: %s\n", needed_name.characters());
String library_name = get_library_name(needed_name);
if (!g_loaded_objects.contains(library_name)) {
load_elf(library_name);
}
}
auto dynamic_object = loader->load_from_image(RTLD_GLOBAL | RTLD_LAZY, g_total_tls_size);
ASSERT(!dynamic_object.is_null());
g_loaded_objects.set(name, dynamic_object.release_nonnull());
if (name == "libc.so") {
initialize_libc();
}
}
static void clear_temporary_objects_mappings()
{
g_loaders.clear();
}
static void display_help()
{
const char message[] =
@ -261,11 +115,24 @@ This helper program loads the shared libraries needed by the program,
prepares the program to run, and runs it. You do not need to invoke
this helper program directly.
)";
write(1, message, sizeof(message));
fprintf(stderr, "%s", message);
}
static FlatPtr loader_main(auxv_t* auxvp)
extern "C" {
// The compiler expects a previous declaration
void _start(int, char**, char**);
void _start(int argc, char** argv, char** envp)
{
char** env;
for (env = envp; *env; ++env) {
}
auxv_t* auxvp = (auxv_t*)++env;
perform_self_relocations(auxvp);
init_libc();
int main_program_fd = -1;
String main_program_name;
for (; auxvp->a_type != AT_NULL; ++auxvp) {
@ -288,62 +155,7 @@ static FlatPtr loader_main(auxv_t* auxvp)
_exit(1);
}
map_library(main_program_name, main_program_fd);
map_dependencies(main_program_name);
VERBOSE("loaded all dependencies");
for ([[maybe_unused]] auto& lib : g_loaders) {
VERBOSE("%s - tls size: %zu, tls offset: %zu\n", lib.key.characters(), lib.value->tls_size(), lib.value->tls_offset());
}
allocate_tls();
load_elf(main_program_name);
auto main_program_lib = g_loaders.get(main_program_name).value();
FlatPtr entry_point = reinterpret_cast<FlatPtr>(main_program_lib->image().entry().as_ptr());
if (main_program_lib->is_dynamic())
entry_point += reinterpret_cast<FlatPtr>(main_program_lib->text_segment_load_address().as_ptr());
VERBOSE("entry point: %p\n", (void*)entry_point);
// This will unmap the temporary memory maps we had for loading the libraries
clear_temporary_objects_mappings();
return entry_point;
}
extern "C" {
// The compiler expects a previous declaration
void _start(int, char**, char**);
void _start(int argc, char** argv, char** envp)
{
g_envp = envp;
char** env;
for (env = envp; *env; ++env) {
}
auxv_t* auxvp = (auxv_t*)++env;
perform_self_relocations(auxvp);
init_libc();
FlatPtr entry = loader_main(auxvp);
VERBOSE("Loaded libs:\n");
for ([[maybe_unused]] auto& obj : g_loaded_objects) {
VERBOSE("%s: %p\n", obj.key.characters(), obj.value->base_address().as_ptr());
}
MainFunction main_function = (MainFunction)(entry);
VERBOSE("jumping to main program entry point: %p\n", main_function);
int rc = main_function(argc, argv, envp);
VERBOSE("rc: %d\n", rc);
if (g_libc_exit != nullptr) {
g_libc_exit(rc);
} else {
_exit(rc);
}
ELF::DynamicLinker::linker_main(move(main_program_name), main_program_fd, argc, argv, envp);
ASSERT_NOT_REACHED();
}
}