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The dynamic loader exists as /usr/lib/Loader.so and is loaded by the kernel when ET_DYN programs are executed. The dynamic loader is responsible for loading the dependencies of the main program, allocating TLS storage, preparing all loaded objects for execution and finally jumping to the entry of the main program.
131 lines
4.3 KiB
C++
131 lines
4.3 KiB
C++
/*
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* Copyright (c) 2018-2020, Andreas Kling <kling@serenityos.org>
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* All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions are met:
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*
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* 1. Redistributions of source code must retain the above copyright notice, this
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* list of conditions and the following disclaimer.
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*
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* 2. Redistributions in binary form must reproduce the above copyright notice,
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* this list of conditions and the following disclaimer in the documentation
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* and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
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* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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* DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE
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* FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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* DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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* SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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* CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
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* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
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* OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include <assert.h>
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#include <dlfcn.h>
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#include <fcntl.h>
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#include <mman.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <sys/stat.h>
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#include <AK/HashMap.h>
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#include <AK/LexicalPath.h>
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#include <AK/RefPtr.h>
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#include <AK/ScopeGuard.h>
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#include <AK/String.h>
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#include <AK/StringBuilder.h>
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#include <LibELF/DynamicLoader.h>
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// NOTE: The string here should never include a trailing newline (according to POSIX)
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String g_dlerror_msg;
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HashMap<String, RefPtr<ELF::DynamicLoader>> g_elf_objects;
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extern "C" {
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int dlclose(void*)
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{
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g_dlerror_msg = "dlclose not implemented!";
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return -1;
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}
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char* dlerror()
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{
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return const_cast<char*>(g_dlerror_msg.characters());
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}
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void* dlopen(const char* filename, int flags)
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{
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// FIXME: Create a global mutex/semaphore/lock for dlopen/dlclose/dlsym and (?) dlerror
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// FIXME: refcount?
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if (!filename) {
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// FIXME: Return the handle for "the main executable"
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// The Serenity Kernel will keep a mapping of the main elf binary resident in memory,
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// But a future dynamic loader might have a different idea/way of letting us access this information
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ASSERT_NOT_REACHED();
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}
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auto basename = LexicalPath(filename).basename();
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auto existing_elf_object = g_elf_objects.get(basename);
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if (existing_elf_object.has_value()) {
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return const_cast<ELF::DynamicLoader*>(existing_elf_object.value());
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}
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int fd = open(filename, O_RDONLY);
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if (!fd) {
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g_dlerror_msg = String::format("Unable to open file %s", filename);
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return nullptr;
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}
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ScopeGuard close_fd_guard([fd]() { close(fd); });
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struct stat file_stats {
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};
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int ret = fstat(fd, &file_stats);
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if (ret < 0) {
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g_dlerror_msg = String::format("Unable to stat file %s", filename);
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return nullptr;
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}
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auto loader = ELF::DynamicLoader::construct(filename, fd, file_stats.st_size);
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if (!loader->is_valid()) {
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g_dlerror_msg = String::format("%s is not a valid ELF dynamic shared object!", filename);
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return nullptr;
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}
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if (!loader->load_from_image(flags,
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0 // total_tls_size = 0, FIXME: Support TLS when using dlopen()
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)) {
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g_dlerror_msg = String::format("Failed to load ELF object %s", filename);
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return nullptr;
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}
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g_elf_objects.set(basename, move(loader));
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g_dlerror_msg = "Successfully loaded ELF object.";
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// we have one refcount already
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return const_cast<ELF::DynamicLoader*>(g_elf_objects.get(basename).value());
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}
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void* dlsym(void* handle, const char* symbol_name)
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{
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// FIXME: When called with a NULL handle we're supposed to search every dso in the process... that'll get expensive
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ASSERT(handle);
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auto* dso = reinterpret_cast<ELF::DynamicLoader*>(handle);
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void* symbol = dso->symbol_for_name(symbol_name);
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if (!symbol) {
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g_dlerror_msg = "Symbol not found";
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return nullptr;
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}
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return symbol;
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}
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} // extern "C"
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