LibELF: Fix support for relocating weak symbols

Having unresolved weak symbols is allowed and we should initialize them to zero.
abyesilyurt · Apr 19, 2021 · 1dab5ca · 1dab5ca
1 parent 97d7450
commit 1dab5ca
Show file tree

Hide file tree

Showing 2 changed files with 20 additions and 10 deletions.
diff --git a/Userland/Libraries/LibELF/DynamicLoader.cpp b/Userland/Libraries/LibELF/DynamicLoader.cpp
@@ -211,7 +211,7 @@ bool DynamicLoader::load_stage_2(unsigned flags, size_t total_tls_size)
 void DynamicLoader::do_main_relocations(size_t total_tls_size)
 {
  auto do_single_relocation = [&](const ELF::DynamicObject::Relocation& relocation) {
- switch (do_relocation(total_tls_size, relocation)) {
+ switch (do_relocation(total_tls_size, relocation, ShouldInitializeWeak::No)) {
  case RelocationResult::Failed:
  dbgln("Loader.so: {} unresolved symbol '{}'", m_filename, relocation.symbol().name());
  VERIFY_NOT_REACHED();
@@ -267,7 +267,7 @@ void DynamicLoader::load_stage_4()
 void DynamicLoader::do_lazy_relocations(size_t total_tls_size)
 {
  for (const auto& relocation : m_unresolved_relocations) {
- if (auto res = do_relocation(total_tls_size, relocation); res != RelocationResult::Success) {
+ if (auto res = do_relocation(total_tls_size, relocation, ShouldInitializeWeak::Yes); res != RelocationResult::Success) {
  dbgln("Loader.so: {} unresolved symbol '{}'", m_filename, relocation.symbol().name());
  VERIFY_NOT_REACHED();
  }
@@ -424,7 +424,7 @@ void DynamicLoader::load_program_headers()
  // FIXME: Initialize the values in the TLS section. Currently, it is zeroed.
 }
 
-DynamicLoader::RelocationResult DynamicLoader::do_relocation(size_t total_tls_size, const ELF::DynamicObject::Relocation& relocation)
+DynamicLoader::RelocationResult DynamicLoader::do_relocation(size_t total_tls_size, const ELF::DynamicObject::Relocation& relocation, ShouldInitializeWeak should_initialize_weak)
 {
  FlatPtr* patch_ptr = nullptr;
  if (is_dynamic())
@@ -462,14 +462,19 @@ DynamicLoader::RelocationResult DynamicLoader::do_relocation(size_t total_tls_si
  case R_386_GLOB_DAT: {
  auto symbol = relocation.symbol();
  auto res = lookup_symbol(symbol);
+ VirtualAddress symbol_location;
  if (!res.has_value()) {
- if (symbol.bind() == STB_WEAK)
- return RelocationResult::ResolveLater;
+ if (symbol.bind() == STB_WEAK) {
+ if (should_initialize_weak == ShouldInitializeWeak::No)
+ return RelocationResult::ResolveLater;
+ } else {
+ // Symbol not found
+ return RelocationResult::Failed;
+ }
 
- // Symbol not found
- return RelocationResult::Failed;
- }
- auto symbol_location = res.value().address;
+ symbol_location = VirtualAddress { (FlatPtr)0 };
+ } else
+ symbol_location = res.value().address;
  VERIFY(symbol_location != m_dynamic_object->base_address());
  *patch_ptr = symbol_location.get();
  break;

diff --git a/Userland/Libraries/LibELF/DynamicLoader.h b/Userland/Libraries/LibELF/DynamicLoader.h
@@ -54,6 +54,11 @@ class LoadedSegment {
  size_t m_size;
 };
 
+enum class ShouldInitializeWeak {
+ Yes,
+ No
+};
+
 class DynamicLoader : public RefCounted<DynamicLoader> {
 public:
  static RefPtr<DynamicLoader> try_create(int fd, String filename);
@@ -145,7 +150,7 @@ class DynamicLoader : public RefCounted<DynamicLoader> {
  Success = 1,
  ResolveLater = 2,
  };
- RelocationResult do_relocation(size_t total_tls_size, const DynamicObject::Relocation&);
+ RelocationResult do_relocation(size_t total_tls_size, const DynamicObject::Relocation&, ShouldInitializeWeak should_initialize_weak);
  size_t calculate_tls_size() const;
 
  String m_filename;