[lldb] Fix LLDBMemoryReader resolving GOT pointers incorrectly

lldb/include/lldb/Core/Section.h

@@ -278,6 +278,9 @@ class Section : public std::enable_shared_from_this<Section>,
   /// return true.
   bool ContainsOnlyDebugInfo() const;
 
+  /// Returns true if this is a global offset table section.
+  bool IsGOTSection() const;
+
 protected:
   ObjectFile *m_obj_file;   // The object file that data for this section should
                             // be read from

lldb/include/lldb/Symbol/ObjectFile.h

@@ -761,6 +761,12 @@ class ObjectFile : public std::enable_shared_from_this<ObjectFile>,
     return false;
   }
 
+  /// Returns true if the section is a global offset table section.
+  virtual bool IsGOTSection(const lldb_private::Section &section) const {
+    assert(section.GetObjectFile() == this && "Wrong object file!");
+    return false;
+  }
+
   /// Get a hash that can be used for caching object file releated information.
   ///
   /// Data for object files can be cached between runs of debug sessions and

lldb/source/Core/Section.cpp

@@ -473,6 +473,10 @@ bool Section::ContainsOnlyDebugInfo() const {
   return false;
 }
 
+bool Section::IsGOTSection() const {
+  return GetObjectFile()->IsGOTSection(*this);
+}
+
 #pragma mark SectionList
 
 SectionList &SectionList::operator=(const SectionList &rhs) {

lldb/source/Plugins/LanguageRuntime/Swift/LLDBMemoryReader.cpp

@@ -317,6 +317,132 @@ LLDBMemoryReader::resolvePointer(swift::remote::RemoteAddress address,
   return tagged_pointer;
 }
 
+swift::reflection::RemoteAddress
+LLDBMemoryReader::resolveIndirectAddressAtOffset(
+    swift::reflection::RemoteAddress address, uint64_t offset,
+    bool directnessEncodedInOffset) {
+  // Usually, simply adding the address with the offset will produce the correct
+  // remote address.
+  //
+  // However, on Apple platforms, the shared cache can coalesce pointers in the
+  // global offset table from multiple images into one location, patch all the
+  // uses to point to the new location, and zero out the original pointer. In
+  // this case, LLDBMemoryReader needs to be conservative and re-fetch the
+  // offset from live memory to ensure it points to the new, coalesced location
+  // instead.
+  Log *log = GetLog(LLDBLog::Types);
+
+  LLDB_LOGV(log,
+            "[MemoryReader::resolveAddressAtOffset] Asked to resolve address "
+            "{0:x} at offset {1:x}",
+            address.getRawAddress(), offset);
+
+  swift::reflection::RemoteAddress offset_address = address + offset;
+
+  if (!readMetadataFromFileCacheEnabled())
+    return offset_address;
+
+  // Addresses in the process can be read directly.
+  if (offset_address.getAddressSpace() ==
+      swift::reflection::RemoteAddress::DefaultAddressSpace)
+    return offset_address;
+
+  // Check if offset_address points to a GOT entry.
+  std::optional<Address> maybeAddr =
+      resolveRemoteAddressFromSymbolObjectFile(offset_address);
+
+  if (!maybeAddr)
+    maybeAddr = remoteAddressToLLDBAddress(offset_address);
+
+  if (!maybeAddr) {
+    LLDB_LOGV(log,
+              "[MemoryReader::resolveAddressAtOffset] could not resolve "
+              "address {0:x}",
+              offset_address.getRawAddress());
+    return offset_address;
+  }
+
+  Address lldb_offset_address = *maybeAddr;
+  if (!lldb_offset_address.IsSectionOffset()) {
+    LLDB_LOGV(
+        log,
+        "[MemoryReader::resolveAddressAtOffset] lldb offset address has no "
+        "section {0:x}",
+        offset_address.getRawAddress());
+    return offset_address;
+  }
+
+  // This is only necessary on Apple platforms.
+  ObjectFile *obj_file = lldb_offset_address.GetModule()->GetObjectFile();
+  if (!obj_file || !obj_file->GetArchitecture().GetTriple().isOSDarwin())
+    return offset_address;
+
+  SectionSP section = lldb_offset_address.GetSection();
+  if (!section->IsGOTSection())
+    return offset_address;
+
+  // offset_address is in a GOT section. Re-read the offset from the base
+  // address in live memory, since the offset in live memory can have been
+  // patched in the shared cache to point somewhere else.
+  std::optional<Address> maybe_lldb_addr =
+      resolveRemoteAddressFromSymbolObjectFile(address);
+
+  if (!maybe_lldb_addr)
+    maybe_lldb_addr = remoteAddressToLLDBAddress(address);
+
+  if (!maybe_lldb_addr) {
+    LLDB_LOGV(log,
+              "[MemoryReader::resolveAddressAtOffset] could not resolve offset "
+              "address {0:x}",
+              address.getRawAddress());
+    return offset_address;
+  }
+
+  auto lldb_addr = *maybe_lldb_addr;
+  Target &target(m_process.GetTarget());
+  Status error;
+  const bool force_live_memory = true;
+  bool did_read_live_memory = false;
+
+  // Relative offsets are always 4 bytes long, regardless of target.
+  uint32_t live_offset = 0;
+  size_t size = sizeof(live_offset);
+  if (size !=
+      target.ReadMemory(lldb_addr, &live_offset, size, error, force_live_memory,
+                        /*load_addr_ptr=*/nullptr, &did_read_live_memory)) {
+    LLDB_LOG(log,
+             "[MemoryReader::resolveAddressAtOffset] Resolve address returned "
+             "different bytes than asked "
+             "for {0:x}",
+             lldb_addr.GetLoadAddress(&target));
+    return offset_address;
+  }
+  if (error.Fail()) {
+    LLDB_LOG(log,
+             "[MemoryReader::resolveAddressAtOffset] memory read returned "
+             "error: {0}",
+             error.AsCString());
+    return offset_address;
+  }
+  // Some Swift metadata encodes the directness directly into the offset,
+  // in that case clear the directness bit.
+  if (directnessEncodedInOffset)
+    live_offset &= ~1u;
+
+  // Now, get the live address counterpart of the lldb address this function
+  // started with, and add the live offset we just read to it.
+  addr_t live_address = lldb_addr.GetLoadAddress(&target);
+  LLDB_LOGV(
+      log,
+      "[MemoryReader::resolveAddressAtOffset] Succesfully resolved address "
+      "into live address {0:x} and offset {1:x} resulting in address {2:x}",
+      live_address, live_offset, live_address + live_offset);
+
+  return swift::remote::RemoteAddress(
+      live_address + live_offset,
+      swift::remote::RemoteAddress::DefaultAddressSpace);
+}
+
 bool LLDBMemoryReader::readBytes(swift::remote::RemoteAddress address,
                                  uint8_t *dest, uint64_t size) {
   auto read_bytes_result = readBytesImpl(address, dest, size);

lldb/source/Plugins/LanguageRuntime/Swift/LLDBMemoryReader.h

@@ -87,6 +87,11 @@ class LLDBMemoryReader : public swift::remote::MemoryReader {
   std::optional<swift::remote::RemoteAddress>
   resolveRemoteAddress(swift::remote::RemoteAddress address) const override;
 
+  swift::reflection::RemoteAddress
+  resolveIndirectAddressAtOffset(swift::reflection::RemoteAddress address,
+                                 uint64_t offset,
+                                 bool directnessEncodedInOffset) override;
+
   bool readBytes(swift::remote::RemoteAddress address, uint8_t *dest,
                  uint64_t size) override;
 

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

@@ -6069,6 +6069,20 @@ Section *ObjectFileMachO::GetMachHeaderSection() {
   return nullptr;
 }
 
+bool ObjectFileMachO::IsGOTSection(const lldb_private::Section &section) const {
+  assert(section.GetObjectFile() == this && "Wrong object file!");
+  SectionSP segment = section.GetParent();
+  if (!segment)
+    return false;
+
+  bool is_data_const_got =
+      segment->GetName() == "__DATA_CONST" && section.GetName() == "__got";
+  bool is_auth_const_ptr =
+      segment->GetName() == "__AUTH_CONST" &&
+      (section.GetName() == "__auth_got" || section.GetName() == "__auth_ptr");
+  return is_data_const_got || is_auth_const_ptr;
+}
+
 bool ObjectFileMachO::SectionIsLoadable(const Section *section) {
   if (!section)
     return false;

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.h

@@ -162,6 +162,8 @@ class ObjectFileMachO : public lldb_private::ObjectFile {
 
   lldb_private::Section *GetMachHeaderSection();
 
+  bool IsGOTSection(const lldb_private::Section &section) const override;
+
   // PluginInterface protocol
   llvm::StringRef GetPluginName() override { return GetPluginNameStatic(); }