lib: Add mlibc

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 844 insertions, 0 deletions

diff --git a/lib/mlibc/options/rtdl/generic/main.cpp b/lib/mlibc/options/rtdl/generic/main.cpp
new file mode 100644
index 0000000..3cff1e4
--- /dev/null
+++ b/lib/mlibc/options/rtdl/generic/main.cpp
@@ -0,0 +1,844 @@
+
+#include <elf.h>
+#include <link.h>
+
+#include <frg/manual_box.hpp>
+#include <frg/small_vector.hpp>
+
+#include <abi-bits/auxv.h>
+#include <mlibc/debug.hpp>
+#include <mlibc/rtdl-sysdeps.hpp>
+#include <mlibc/rtdl-config.hpp>
+#include <mlibc/rtdl-abi.hpp>
+#include <mlibc/stack_protector.hpp>
+#include <internal-config.h>
+#include <abi-bits/auxv.h>
+
+#include "elf.hpp"
+#include "linker.hpp"
+
+#if __MLIBC_POSIX_OPTION
+#include <dlfcn.h>
+#endif
+
+#define HIDDEN  __attribute__((__visibility__("hidden")))
+#define EXPORT  __attribute__((__visibility__("default")))
+
+static constexpr bool logEntryExit = false;
+static constexpr bool logStartup = false;
+static constexpr bool logDlCalls = false;
+
+#ifndef MLIBC_STATIC_BUILD
+extern HIDDEN void *_GLOBAL_OFFSET_TABLE_[];
+extern HIDDEN elf_dyn _DYNAMIC[];
+#endif
+
+namespace mlibc {
+	// Declared in options/internal/mlibc/tcb.hpp.
+	bool tcb_available_flag = false;
+}
+
+mlibc::RtdlConfig rtdlConfig;
+
+bool ldShowAuxv = false;
+
+uintptr_t *entryStack;
+frg::manual_box<ObjectRepository> initialRepository;
+frg::manual_box<Scope> globalScope;
+
+frg::manual_box<RuntimeTlsMap> runtimeTlsMap;
+
+// We use a small vector of size 4 to avoid memory allocation for the default library paths
+frg::manual_box<frg::small_vector<frg::string_view, 4, MemoryAllocator>> libraryPaths;
+
+frg::manual_box<frg::vector<frg::string_view, MemoryAllocator>> preloads;
+
+static SharedObject *executableSO;
+extern HIDDEN char __ehdr_start[];
+
+// Global debug interface variable
+DebugInterface globalDebugInterface;
+
+#ifndef MLIBC_STATIC_BUILD
+
+// Use a PC-relative instruction sequence to find our runtime load address.
+uintptr_t getLdsoBase() {
+#if defined(__x86_64__) || defined(__i386__) || defined(__aarch64__)
+	// On x86_64, the first GOT entry holds the link-time address of _DYNAMIC.
+	// TODO: This isn't guaranteed on AArch64, so this might fail with some linkers.
+	auto linktime_dynamic = reinterpret_cast<uintptr_t>(_GLOBAL_OFFSET_TABLE_[0]);
+	auto runtime_dynamic = reinterpret_cast<uintptr_t>(_DYNAMIC);
+	return runtime_dynamic - linktime_dynamic;
+#elif defined(__riscv)
+	return reinterpret_cast<uintptr_t>(&__ehdr_start);
+#endif
+}
+
+// Relocates the dynamic linker (i.e. this DSO) itself.
+// Assumptions:
+// - There are no references to external symbols.
+// Note that this code is fragile in the sense that it must not contain relocations itself.
+// TODO: Use tooling to verify this at compile time.
+extern "C" void relocateSelf() {
+	size_t rela_offset = 0;
+	size_t rela_size = 0;
+	size_t rel_offset = 0;
+	size_t rel_size = 0;
+	size_t relr_offset = 0;
+	size_t relr_size = 0;
+	for(size_t i = 0; _DYNAMIC[i].d_tag != DT_NULL; i++) {
+		auto ent = &_DYNAMIC[i];
+		switch(ent->d_tag) {
+		case DT_REL: rel_offset = ent->d_un.d_ptr; break;
+		case DT_RELSZ: rel_size = ent->d_un.d_val; break;
+		case DT_RELA: rela_offset = ent->d_un.d_ptr; break;
+		case DT_RELASZ: rela_size = ent->d_un.d_val; break;
+		case DT_RELR: relr_offset = ent->d_un.d_ptr; break;
+		case DT_RELRSZ: relr_size = ent->d_un.d_val; break;
+		}
+	}
+
+	auto ldso_base = getLdsoBase();
+
+	__ensure((rel_offset != 0) ^ (rela_offset != 0));
+
+	for(size_t disp = 0; disp < rela_size; disp += sizeof(elf_rela)) {
+		auto reloc = reinterpret_cast<elf_rela *>(ldso_base + rela_offset + disp);
+
+		auto type = ELF_R_TYPE(reloc->r_info);
+		if(ELF_R_SYM(reloc->r_info))
+			__builtin_trap();
+
+		auto p = reinterpret_cast<uint64_t *>(ldso_base + reloc->r_offset);
+		switch(type) {
+		case R_RELATIVE:
+			*p = ldso_base + reloc->r_addend;
+			break;
+		default:
+			__builtin_trap();
+		}
+	}
+
+	for(size_t disp = 0; disp < rel_size; disp += sizeof(elf_rel)) {
+		auto reloc = reinterpret_cast<elf_rel *>(ldso_base + rel_offset + disp);
+
+		auto type = ELF_R_TYPE(reloc->r_info);
+		if(ELF_R_SYM(reloc->r_info))
+			__builtin_trap();
+
+		auto p = reinterpret_cast<uint64_t *>(ldso_base + reloc->r_offset);
+		switch(type) {
+		case R_RELATIVE:
+			*p += ldso_base;
+			break;
+		default:
+			__builtin_trap();
+		}
+	}
+
+	elf_addr *addr = nullptr;
+	for(size_t disp = 0; disp < relr_size; disp += sizeof(elf_relr)) {
+		auto entry = *(elf_relr *)(ldso_base + relr_offset + disp);
+
+		// Even entry indicates the beginning address.
+		if(!(entry & 1)) {
+			addr = (elf_addr *)(ldso_base + entry);
+			__ensure(addr);
+			*addr++ += ldso_base;
+		}else {
+			// Odd entry indicates entry is a bitmap of the subsequent locations to be relocated.
+			for(int i = 0; entry; ++i) {
+				if(entry & 1) {
+					addr[i] += ldso_base;
+				}
+				entry >>= 1;
+			}
+
+			// Each entry describes at max 63 (on 64bit) or 31 (on 32bit) subsequent locations.
+			addr += CHAR_BIT * sizeof(elf_relr) - 1;
+		}
+	}
+}
+#endif
+
+extern "C" void *lazyRelocate(SharedObject *object, unsigned int rel_index) {
+	__ensure(object->lazyExplicitAddend);
+	auto reloc = (elf_rela *)(object->baseAddress + object->lazyRelocTableOffset
+			+ rel_index * sizeof(elf_rela));
+	auto type = ELF_R_TYPE(reloc->r_info);
+	auto symbol_index = ELF_R_SYM(reloc->r_info);
+
+	__ensure(type == R_X86_64_JUMP_SLOT);
+	__ensure(ELF_CLASS == ELFCLASS64);
+
+	auto symbol = (elf_sym *)(object->baseAddress + object->symbolTableOffset
+			+ symbol_index * sizeof(elf_sym));
+	ObjectSymbol r(object, symbol);
+	auto p = Scope::resolveGlobalOrLocal(*globalScope, object->localScope, r.getString(), object->objectRts, 0);
+	if(!p)
+		mlibc::panicLogger() << "Unresolved JUMP_SLOT symbol" << frg::endlog;
+
+	//mlibc::infoLogger() << "Lazy relocation to " << symbol_str
+	//		<< " resolved to " << pointer << frg::endlog;
+
+	*(uint64_t *)(object->baseAddress + reloc->r_offset) = p->virtualAddress();
+	return (void *)p->virtualAddress();
+}
+
+extern "C" [[ gnu::visibility("default") ]] void *__rtdl_allocateTcb() {
+	auto tcb = allocateTcb();
+	initTlsObjects(tcb, globalScope->_objects, false);
+	return tcb;
+}
+
+extern "C" {
+	[[ gnu::visibility("hidden") ]] void dl_debug_state() {
+		// This function is used to signal changes in the debugging link map,
+		// GDB just sets a breakpoint on this function and we can call it
+		// everytime we update the link map. We don't need to implement
+		// anything besides defining and calling it.
+	}
+}
+
+extern "C" [[gnu::alias("dl_debug_state"), gnu::visibility("default")]] void _dl_debug_state() noexcept;
+
+// This symbol can be used by GDB to find the global interface structure
+[[ gnu::visibility("default") ]] DebugInterface *_dl_debug_addr = &globalDebugInterface;
+
+static frg::vector<frg::string_view, MemoryAllocator> parseList(frg::string_view paths, frg::string_view separators) {
+	frg::vector<frg::string_view, MemoryAllocator> list{getAllocator()};
+
+	size_t p = 0;
+	while(p < paths.size()) {
+		size_t s; // Offset of next colon or end of string.
+		if(size_t cs = paths.find_first_of(separators, p); cs != size_t(-1)) {
+			s = cs;
+		}else{
+			s = paths.size();
+		}
+
+		auto path = paths.sub_string(p, s - p);
+		p = s + 1;
+
+		if(path.size() == 0)
+			continue;
+
+		if(path.ends_with("/")) {
+			size_t i = path.size() - 1;
+			while(i > 0 && path[i] == '/')
+				i--;
+			path = path.sub_string(0, i + 1);
+		}
+
+		if(path == "/")
+			path = "";
+
+		list.push_back(path);
+	}
+
+	return list;
+}
+
+extern "C" void *interpreterMain(uintptr_t *entry_stack) {
+	if(logEntryExit)
+		mlibc::infoLogger() << "Entering ld.so" << frg::endlog;
+	entryStack = entry_stack;
+	runtimeTlsMap.initialize();
+	libraryPaths.initialize(getAllocator());
+	preloads.initialize(getAllocator());
+
+	void *phdr_pointer = 0;
+	size_t phdr_entry_size = 0;
+	size_t phdr_count = 0;
+	void *entry_pointer = 0;
+	void *stack_entropy = nullptr;
+
+	const char *execfn = "(executable)";
+
+#ifndef MLIBC_STATIC_BUILD
+	using ctor_fn = void(*)(void);
+
+	ctor_fn *ldso_ctors = nullptr;
+	size_t num_ldso_ctors = 0;
+
+	auto ldso_base = getLdsoBase();
+	if(logStartup) {
+		mlibc::infoLogger() << "ldso: Own base address is: 0x"
+				<< frg::hex_fmt(ldso_base) << frg::endlog;
+		mlibc::infoLogger() << "ldso: Own dynamic section is at: " << _DYNAMIC << frg::endlog;
+	}
+
+#ifdef __x86_64__
+	// These entries are reserved on x86_64.
+	// TODO: Use a fake PLT stub that reports an error message?
+	_GLOBAL_OFFSET_TABLE_[1] = 0;
+	_GLOBAL_OFFSET_TABLE_[2] = 0;
+#endif
+
+	// Validate our own dynamic section.
+	// Here, we make sure that the dynamic linker does not need relocations itself.
+	uintptr_t strtab_offset = 0;
+	uintptr_t soname_str = 0;
+	for(size_t i = 0; _DYNAMIC[i].d_tag != DT_NULL; i++) {
+		auto ent = &_DYNAMIC[i];
+		switch(ent->d_tag) {
+		case DT_STRTAB: strtab_offset = ent->d_un.d_ptr; break;
+		case DT_SONAME: soname_str = ent->d_un.d_val; break;
+		case DT_INIT_ARRAY: ldso_ctors = reinterpret_cast<ctor_fn *>(ent->d_un.d_ptr + ldso_base); break;
+		case DT_INIT_ARRAYSZ: num_ldso_ctors = ent->d_un.d_val / sizeof(ctor_fn); break;
+		case DT_HASH:
+		case DT_GNU_HASH:
+		case DT_STRSZ:
+		case DT_SYMTAB:
+		case DT_SYMENT:
+		case DT_RELA:
+		case DT_RELASZ:
+		case DT_RELAENT:
+		case DT_RELACOUNT:
+		case DT_DEBUG:
+		case DT_REL:
+		case DT_RELSZ:
+		case DT_RELENT:
+		case DT_RELCOUNT:
+		case DT_RELR:
+		case DT_RELRSZ:
+		case DT_RELRENT:
+			continue;
+		default:
+			__ensure(!"Unexpected dynamic entry in program interpreter");
+		}
+	}
+	__ensure(strtab_offset);
+	__ensure(soname_str);
+
+	// Find the auxiliary vector by skipping args and environment.
+	auto aux = entryStack;
+	aux += *aux + 1; // First, we skip argc and all args.
+	__ensure(!*aux);
+	aux++;
+	while(*aux) { // Loop through the environment.
+		auto env = reinterpret_cast<char *>(*aux);
+		frg::string_view view{env};
+		size_t s = view.find_first('=');
+
+		if(s == size_t(-1))
+			mlibc::panicLogger() << "rtdl: environment '" << env << "' is missing a '='" << frg::endlog;
+
+		auto name = view.sub_string(0, s);
+		auto value = const_cast<char *>(view.data() + s + 1);
+
+		if(name == "LD_SHOW_AUXV" && *value && *value != '0') {
+			ldShowAuxv = true;
+		}else if(name == "LD_LIBRARY_PATH" && *value) {
+			for(auto path : parseList(value, ":;"))
+				libraryPaths->push_back(path);
+		}else if(name == "LD_PRELOAD" && *value) {
+			*preloads = parseList(value, " :");
+		}
+
+		aux++;
+	}
+	aux++;
+
+	// Add default library paths
+	libraryPaths->push_back("/lib");
+	libraryPaths->push_back("/lib64");
+	libraryPaths->push_back("/usr/lib");
+	libraryPaths->push_back("/usr/lib64");
+
+	// Parse the actual vector.
+	while(true) {
+		auto value = aux + 1;
+		if(!(*aux))
+			break;
+
+		if(ldShowAuxv) {
+			switch(*aux) {
+				case AT_PHDR: mlibc::infoLogger() << "AT_PHDR: 0x" << frg::hex_fmt{*value} << frg::endlog; break;
+				case AT_PHENT: mlibc::infoLogger() << "AT_PHENT: " << *value << frg::endlog; break;
+				case AT_PHNUM: mlibc::infoLogger() << "AT_PHNUM: " << *value << frg::endlog; break;
+				case AT_ENTRY: mlibc::infoLogger() << "AT_ENTRY: 0x" << frg::hex_fmt{*value} << frg::endlog; break;
+				case AT_PAGESZ: mlibc::infoLogger() << "AT_PAGESZ: " << *value << frg::endlog; break;
+				case AT_BASE: mlibc::infoLogger() << "AT_BASE: 0x" << frg::hex_fmt{*value} << frg::endlog; break;
+				case AT_FLAGS: mlibc::infoLogger() << "AT_FLAGS: 0x" << frg::hex_fmt{*value} << frg::endlog; break;
+				case AT_NOTELF: mlibc::infoLogger() << "AT_NOTELF: " << frg::hex_fmt{*value} << frg::endlog; break;
+				case AT_UID: mlibc::infoLogger() << "AT_UID: " << *value << frg::endlog; break;
+				case AT_EUID: mlibc::infoLogger() << "AT_EUID: " << *value << frg::endlog; break;
+				case AT_GID: mlibc::infoLogger() << "AT_GID: " << *value << frg::endlog; break;
+				case AT_EGID: mlibc::infoLogger() << "AT_EGID: " << *value << frg::endlog; break;
+#ifdef AT_PLATFORM
+ 				case AT_PLATFORM: mlibc::infoLogger() << "AT_PLATFORM: " << reinterpret_cast<const char *>(*value) << frg::endlog; break;
+#endif
+#ifdef AT_HWCAP
+				case AT_HWCAP: mlibc::infoLogger() << "AT_HWCAP: " << frg::hex_fmt{*value} << frg::endlog; break;
+#endif
+#ifdef AT_CLKTCK
+				case AT_CLKTCK: mlibc::infoLogger() << "AT_CLKTCK: " << *value << frg::endlog; break;
+#endif
+#ifdef AT_FPUCW
+				case AT_FPUCW: mlibc::infoLogger() << "AT_FPUCW: " << frg::hex_fmt{*value} << frg::endlog; break;
+#endif
+#ifdef AT_SECURE
+ 				case AT_SECURE: mlibc::infoLogger() << "AT_SECURE: " << *value << frg::endlog; break;
+#endif
+#ifdef AT_RANDOM
+ 				case AT_RANDOM: mlibc::infoLogger() << "AT_RANDOM: 0x" << frg::hex_fmt{*value} << frg::endlog; break;
+#endif
+#ifdef AT_EXECFN
+				case AT_EXECFN: mlibc::infoLogger() << "AT_EXECFN: " << reinterpret_cast<const char *>(*value) << frg::endlog; break;
+#endif
+#ifdef AT_SYSINFO_EHDR
+				case AT_SYSINFO_EHDR: mlibc::infoLogger() << "AT_SYSINFO_EHDR: 0x" << frg::hex_fmt{*value} << frg::endlog; break;
+#endif
+			}
+		}
+
+		// TODO: Whitelist auxiliary vector entries here?
+		switch(*aux) {
+			case AT_PHDR: phdr_pointer = reinterpret_cast<void *>(*value); break;
+			case AT_PHENT: phdr_entry_size = *value; break;
+			case AT_PHNUM: phdr_count = *value; break;
+			case AT_ENTRY: entry_pointer = reinterpret_cast<void *>(*value); break;
+			case AT_EXECFN: execfn = reinterpret_cast<const char *>(*value); break;
+			case AT_RANDOM: stack_entropy = reinterpret_cast<void*>(*value); break;
+			case AT_SECURE: rtdlConfig.secureRequired = reinterpret_cast<uintptr_t>(*value); break;
+		}
+
+		aux += 2;
+	}
+	globalDebugInterface.base = reinterpret_cast<void*>(ldso_base);
+
+// This is here because libgcc will add a global constructor on glibc Linux
+// (which is what it believes we are due to the aarch64-linux-gnu toolchain)
+// in order to check if LSE atomics are supported.
+//
+// This is not necessary on a custom Linux toolchain and is purely an artifact of
+// using the host toolchain.
+#if defined(__aarch64__) && defined(__gnu_linux__)
+	for (size_t i = 0; i < num_ldso_ctors; i++) {
+		if(logStartup)
+			mlibc::infoLogger() << "ldso: Running own constructor at "
+					<< reinterpret_cast<void *>(ldso_ctors[i])
+					<< frg::endlog;
+		ldso_ctors[i]();
+	}
+#else
+	if (num_ldso_ctors > 0) {
+		mlibc::panicLogger() << "ldso: Found unexpected own global constructor(s), init_array starts at: "
+				<< ldso_ctors
+				<< frg::endlog;
+	}
+#endif
+
+#else
+	auto ehdr = reinterpret_cast<elf_ehdr*>(__ehdr_start);
+	phdr_pointer = reinterpret_cast<void*>((uintptr_t)ehdr->e_phoff + (uintptr_t)ehdr);
+	phdr_entry_size = ehdr->e_phentsize;
+	phdr_count = ehdr->e_phnum;
+	entry_pointer = reinterpret_cast<void*>(ehdr->e_entry);
+#endif
+	__ensure(phdr_pointer);
+	__ensure(entry_pointer);
+
+	if(logStartup)
+		mlibc::infoLogger() << "ldso: Executable PHDRs are at " << phdr_pointer
+				<< frg::endlog;
+
+	// perform the initial dynamic linking
+	initialRepository.initialize();
+
+	globalScope.initialize(true);
+
+	// Add the dynamic linker, as well as the exectuable to the repository.
+#ifndef MLIBC_STATIC_BUILD
+	auto ldso_soname = reinterpret_cast<const char *>(ldso_base + strtab_offset + soname_str);
+	auto ldso = initialRepository->injectObjectFromDts(ldso_soname,
+		frg::string<MemoryAllocator> { getAllocator() },
+		ldso_base, _DYNAMIC, 1);
+	ldso->phdrPointer = phdr_pointer;
+	ldso->phdrCount = phdr_count;
+	ldso->phdrEntrySize = phdr_entry_size;
+
+	// TODO: support non-zero base addresses?
+	executableSO = initialRepository->injectObjectFromPhdrs(execfn,
+		frg::string<MemoryAllocator> { execfn, getAllocator() },
+		phdr_pointer, phdr_entry_size, phdr_count, entry_pointer, 1);
+
+	// We can't initialise the ldso object after the executable SO,
+	// so we have to set the ldso path after loading both.
+	ldso->path = executableSO->interpreterPath;
+
+#else
+	executableSO = initialRepository->injectStaticObject(execfn,
+			frg::string<MemoryAllocator>{ execfn, getAllocator() },
+			phdr_pointer, phdr_entry_size, phdr_count, entry_pointer, 1);
+	globalDebugInterface.base = (void*)executableSO->baseAddress;
+#endif
+
+	globalDebugInterface.head = &executableSO->linkMap;
+	executableSO->inLinkMap = true;
+	Loader linker{globalScope.get(), executableSO, true, 1};
+	linker.linkObjects(executableSO);
+
+	mlibc::initStackGuard(stack_entropy);
+
+	auto tcb = allocateTcb();
+	if(mlibc::sys_tcb_set(tcb))
+		__ensure(!"sys_tcb_set() failed");
+	tcb->tid = mlibc::this_tid();
+	mlibc::tcb_available_flag = true;
+
+	globalDebugInterface.ver = 1;
+	globalDebugInterface.brk = &dl_debug_state;
+	globalDebugInterface.state = 0;
+	dl_debug_state();
+
+	linker.initObjects();
+
+	if(logEntryExit)
+		mlibc::infoLogger() << "Leaving ld.so, jump to "
+				<< (void *)executableSO->entry << frg::endlog;
+	return executableSO->entry;
+}
+
+const char *lastError;
+
+extern "C" [[ gnu::visibility("default") ]] uintptr_t *__dlapi_entrystack() {
+	return entryStack;
+}
+
+extern "C" [[ gnu::visibility("default") ]]
+const char *__dlapi_error() {
+	auto error = lastError;
+	lastError = nullptr;
+	return error;
+}
+
+extern "C" [[ gnu::visibility("default") ]]
+void *__dlapi_get_tls(struct __abi_tls_entry *entry) {
+	return reinterpret_cast<char *>(accessDtv(entry->object)) + entry->offset;
+}
+
+extern "C" [[ gnu::visibility("default") ]]
+const mlibc::RtdlConfig &__dlapi_get_config() {
+	return rtdlConfig;
+}
+
+#if __MLIBC_POSIX_OPTION
+
+extern "C" [[ gnu::visibility("default") ]]
+void *__dlapi_open(const char *file, int flags, void *returnAddress) {
+	if (logDlCalls)
+		mlibc::infoLogger() << "rtdl: __dlapi_open(" << (file ? file : "nullptr") << ")" << frg::endlog;
+
+	if (flags & RTLD_DEEPBIND)
+		mlibc::infoLogger() << "rtdl: dlopen(RTLD_DEEPBIND) is unsupported" << frg::endlog;
+
+	if(!file)
+		return executableSO;
+
+	// TODO: Thread-safety!
+	auto rts = rtsCounter++;
+
+	SharedObject *object;
+	if (flags & RTLD_NOLOAD) {
+		object = initialRepository->findLoadedObject(file);
+		if (object && object->globalRts == 0 && (flags & RTLD_GLOBAL)) {
+			// The object was opened with RTLD_LOCAL, but we are called with RTLD_NOLOAD | RTLD_GLOBAL.
+			// According to the man page, we should promote to the global scope here.
+			object->globalRts = rts;
+			globalScope->appendObject(object);
+		}
+	} else {
+		bool isGlobal = flags & RTLD_GLOBAL;
+		Scope *newScope = isGlobal ? globalScope.get() : nullptr;
+
+		frg::expected<LinkerError, SharedObject *> objectResult;
+		if (frg::string_view{file}.find_first('/') == size_t(-1)) {
+			// In order to know which RUNPATH / RPATH to process, we must find the calling object.
+			SharedObject *origin = initialRepository->findCaller(returnAddress);
+			if (!origin) {
+				mlibc::panicLogger() << "rtdl: unable to determine calling object of dlopen "
+					<< "(ra = " << returnAddress << ")" << frg::endlog;
+			}
+
+			objectResult = initialRepository->requestObjectWithName(file, origin, newScope, !isGlobal, rts);
+		} else {
+			objectResult = initialRepository->requestObjectAtPath(file, newScope, !isGlobal, rts);
+		}
+
+		if(!objectResult) {
+			switch (objectResult.error()) {
+			case LinkerError::success:
+				__builtin_unreachable();
+			case LinkerError::notFound:
+				lastError = "Cannot locate requested DSO";
+				break;
+			case LinkerError::fileTooShort:
+				lastError = "File too short";
+				break;
+			case LinkerError::notElf:
+				lastError = "File is not an ELF file";
+				break;
+			case LinkerError::wrongElfType:
+				lastError = "File has wrong ELF type";
+				break;
+			case LinkerError::outOfMemory:
+				lastError = "Out of memory";
+				break;
+			case LinkerError::invalidProgramHeader:
+				lastError = "File has invalid program header";
+				break;
+			}
+			return nullptr;
+		}
+		object = objectResult.value();
+
+		Loader linker{object->localScope, nullptr, false, rts};
+		linker.linkObjects(object);
+		linker.initObjects();
+	}
+
+	dl_debug_state();
+
+	return object;
+}
+
+extern "C" [[ gnu::visibility("default") ]]
+void *__dlapi_resolve(void *handle, const char *string, void *returnAddress) {
+	if (logDlCalls) {
+		const char *name;
+		bool quote = false;
+		if (handle == RTLD_DEFAULT) {
+			name = "RTLD_DEFAULT";
+		} else if (handle == RTLD_NEXT) {
+			name = "RTLD_NEXT";
+		} else {
+			name = ((SharedObject *)handle)->name.data();
+			quote = true;
+		}
+
+		mlibc::infoLogger() << "rtdl: __dlapi_resolve(" << (quote ? "\"" : "") << name
+			<< (quote ? "\"" : "") << ", \"" << string << "\")" << frg::endlog;
+	}
+
+	frg::optional<ObjectSymbol> target;
+
+	if (handle == RTLD_DEFAULT) {
+		target = globalScope->resolveSymbol(string, 0, 0);
+	} else if (handle == RTLD_NEXT) {
+		SharedObject *origin = initialRepository->findCaller(returnAddress);
+		if (!origin) {
+			mlibc::panicLogger() << "rtdl: unable to determine calling object of dlsym "
+				<< "(ra = " << returnAddress << ")" << frg::endlog;
+		}
+
+		target = Scope::resolveGlobalOrLocalNext(*globalScope, origin->localScope, string, origin);
+	} else {
+		// POSIX does not unambiguously state how dlsym() is supposed to work; it just
+		// states that "The symbol resolution algorithm used shall be dependency order
+		// as described in dlopen()".
+		//
+		// Linux libc's lookup the symbol in the given DSO and all of its dependencies
+		// in breadth-first order. That is also what we implement here.
+		//
+		// Note that this *differs* from the algorithm that is used for relocations
+		// (since the algorithm used for relocations takes (i) the global scope,
+		// and (ii) the local scope of the DSO into account (which can contain more objects
+		// than just the dependencies of the DSO, if the DSO was loaded as a dependency
+		// of a dlopen()ed DSO).
+
+		frg::vector<SharedObject *, MemoryAllocator> queue{getAllocator()};
+
+		struct Token { };
+		frg::hash_map<
+				SharedObject *, Token,
+				frg::hash<SharedObject *>, MemoryAllocator
+		> visited{frg::hash<SharedObject *>{}, getAllocator()};
+
+		auto root = reinterpret_cast<SharedObject *>(handle);
+		visited.insert(root, Token{});
+		queue.push_back(root);
+
+		for(size_t i = 0; i < queue.size(); i++) {
+			auto current = queue[i];
+
+			target = resolveInObject(current, string);
+			if(target)
+				break;
+
+			for(auto dep : current->dependencies) {
+				if(visited.get(dep))
+					continue;
+				visited.insert(dep, Token{});
+				queue.push_back(dep);
+			}
+		}
+	}
+
+	if (!target) {
+		if (logDlCalls)
+			mlibc::infoLogger() << "rtdl: could not resolve \"" << string << "\"" << frg::endlog;
+
+		lastError = "Cannot resolve requested symbol";
+		return nullptr;
+	}
+	return reinterpret_cast<void *>(target->virtualAddress());
+}
+
+struct __dlapi_symbol {
+	const char *file;
+	void *base;
+	const char *symbol;
+	void *address;
+};
+
+extern "C" [[ gnu::visibility("default") ]]
+int __dlapi_reverse(const void *ptr, __dlapi_symbol *info) {
+	if (logDlCalls)
+		mlibc::infoLogger() << "rtdl: __dlapi_reverse(" << ptr << ")" << frg::endlog;
+
+	for(size_t i = 0; i < initialRepository->loadedObjects.size(); i++) {
+		auto object = initialRepository->loadedObjects[i];
+
+		auto eligible = [&] (ObjectSymbol cand) {
+			if(cand.symbol()->st_shndx == SHN_UNDEF)
+				return false;
+
+			auto bind = ELF_ST_BIND(cand.symbol()->st_info);
+			if(bind != STB_GLOBAL && bind != STB_WEAK)
+				return false;
+
+			return true;
+		};
+
+		auto hash_table = (Elf64_Word *)(object->baseAddress + object->hashTableOffset);
+		auto num_symbols = hash_table[1];
+		for(size_t i = 0; i < num_symbols; i++) {
+			ObjectSymbol cand{object, (elf_sym *)(object->baseAddress
+					+ object->symbolTableOffset + i * sizeof(elf_sym))};
+			if(eligible(cand) && cand.virtualAddress() == reinterpret_cast<uintptr_t>(ptr)) {
+				if (logDlCalls)
+					mlibc::infoLogger() << "rtdl: Found symbol " << cand.getString() << " in object "
+							<< object->path << frg::endlog;
+
+				info->file = object->path.data();
+				info->base = reinterpret_cast<void *>(object->baseAddress);
+				info->symbol = cand.getString();
+				info->address = reinterpret_cast<void *>(cand.virtualAddress());
+				return 0;
+			}
+		}
+	}
+
+	// Not found, find the DSO it should be in.
+	for(size_t i = 0; i < initialRepository->loadedObjects.size(); i++) {
+		auto object = initialRepository->loadedObjects[i];
+
+		for(size_t j = 0; j < object->phdrCount; j++) {
+			auto phdr = (elf_phdr *)((uintptr_t)object->phdrPointer + j * object->phdrEntrySize);
+			if(phdr->p_type != PT_LOAD) {
+				continue;
+			}
+			uintptr_t start = object->baseAddress + phdr->p_vaddr;
+			uintptr_t end = start + phdr->p_memsz;
+			if(reinterpret_cast<uintptr_t>(ptr) >= start && reinterpret_cast<uintptr_t>(ptr) < end) {
+				mlibc::infoLogger() << "rtdl: Found DSO " << object->path << frg::endlog;
+				info->file = object->path.data();
+				info->base = reinterpret_cast<void *>(object->baseAddress);
+				info->symbol = nullptr;
+				info->address = 0;
+				return 0;
+			}
+		}
+	}
+
+	if (logDlCalls)
+		mlibc::infoLogger() << "rtdl: Could not find symbol in __dlapi_reverse()" << frg::endlog;
+
+	return -1;
+}
+
+extern "C" [[ gnu::visibility("default") ]]
+int __dlapi_close(void *) {
+	if (logDlCalls)
+		mlibc::infoLogger() << "mlibc: dlclose() is a no-op" << frg::endlog;
+	return 0;
+}
+
+#endif
+
+extern "C" [[ gnu::visibility("default") ]]
+int __dlapi_iterate_phdr(int (*callback)(struct dl_phdr_info *, size_t, void*), void *data) {
+	int last_return = 0;
+	for (auto object : initialRepository->loadedObjects) {
+		struct dl_phdr_info info;
+		info.dlpi_addr = object->baseAddress;
+		info.dlpi_name = object->name.data();
+
+		if(object->isMainObject) {
+			info.dlpi_name = "";
+		} else {
+			info.dlpi_name = object->name.data();
+		}
+		info.dlpi_phdr = static_cast<ElfW(Phdr)*>(object->phdrPointer);
+		info.dlpi_phnum = object->phdrCount;
+		info.dlpi_adds = rtsCounter;
+		info.dlpi_subs = 0; // TODO(geert): implement dlclose().
+		if (object->tlsModel != TlsModel::null)
+			info.dlpi_tls_modid = object->tlsIndex;
+		else
+			info.dlpi_tls_modid = 0;
+		info.dlpi_tls_data = tryAccessDtv(object);
+
+		last_return = callback(&info, sizeof(struct dl_phdr_info), data);
+		if(last_return)
+			return last_return;
+	}
+
+	return last_return;
+}
+
+extern "C" [[ gnu::visibility("default") ]]
+void __dlapi_enter(uintptr_t *entry_stack) {
+#if MLIBC_STATIC_BUILD
+	interpreterMain(entry_stack);
+#else
+	(void)entry_stack;
+#endif
+}
+
+// XXX(qookie):
+// This is here because libgcc will call into __getauxval on glibc Linux
+// (which is what it believes we are due to the aarch64-linux-gnu toolchain)
+// in order to find AT_HWCAP to discover if LSE atomics are supported.
+//
+// This is not necessary on a custom Linux toolchain and is purely an artifact of
+// using the host toolchain.
+
+// __gnu_linux__ is the define checked by libgcc
+#if defined(__aarch64__) && defined(__gnu_linux__) && !defined(MLIBC_STATIC_BUILD)
+
+extern "C" unsigned long __getauxval(unsigned long type) {
+	// Find the auxiliary vector by skipping args and environment.
+	auto aux = entryStack;
+	aux += *aux + 1; // Skip argc and all arguments
+	__ensure(!*aux);
+	aux++;
+	while(*aux) // Now, we skip the environment.
+		aux++;
+	aux++;
+
+	// Parse the auxiliary vector.
+	while(true) {
+		auto value = aux + 1;
+		if(*aux == AT_NULL) {
+			return 0;
+		}else if(*aux == type) {
+			return *value;
+		}
+		aux += 2;
+	}
+}
+
+#endif