[lldb][AIX] Header Parsing for XCOFF Object File in AIX (llvm#116338)

This PR is in reference to porting LLDB on AIX.

Link to discussions on llvm discourse and github:
1. https://discourse.llvm.org/t/port-lldb-to-ibm-aix/80640
2. llvm#101657
The complete changes for porting are present in this draft PR:
llvm#102601

Added XCOFF Object File Header Parsing for AIX.

Details about XCOFF file format on AIX:
[XCOFF](https://www.ibm.com/docs/en/aix/7.3?topic=formats-xcoff-object-file-format)

Author: DhruvSrivastavaX

lldb/source/Plugins/ObjectFile/XCOFF/ObjectFileXCOFF.cpp

@@ -79,9 +79,44 @@ ObjectFile *ObjectFileXCOFF::CreateInstance(const lldb::ModuleSP &module_sp,
   if (!objfile_up)
     return nullptr;
 
+  // Cache xcoff binary.
+  if (!objfile_up->CreateBinary())
+    return nullptr;
+
+  if (!objfile_up->ParseHeader())
+    return nullptr;
+
   return objfile_up.release();
 }
 
+bool ObjectFileXCOFF::CreateBinary() {
+  if (m_binary)
+    return true;
+
+  Log *log = GetLog(LLDBLog::Object);
+
+  auto binary = llvm::object::ObjectFile::createObjectFile(
+      llvm::MemoryBufferRef(toStringRef(m_data.GetData()),
+                            m_file.GetFilename().GetStringRef()),
+      file_magic::xcoff_object_64);
+  if (!binary) {
+    LLDB_LOG_ERROR(log, binary.takeError(),
+                   "Failed to create binary for file ({1}): {0}", m_file);
+    return false;
+  }
+  // Make sure we only handle XCOFF format.
+  m_binary =
+      llvm::unique_dyn_cast<llvm::object::XCOFFObjectFile>(std::move(*binary));
+  if (!m_binary)
+    return false;
+
+  LLDB_LOG(log, "this = {0}, module = {1} ({2}), file = {3}, binary = {4}",
+           this, GetModule().get(), GetModule()->GetSpecificationDescription(),
+           m_file.GetPath(), m_binary.get());
+
+  return true;
+}
+
 ObjectFile *ObjectFileXCOFF::CreateMemoryInstance(
     const lldb::ModuleSP &module_sp, WritableDataBufferSP data_sp,
     const lldb::ProcessSP &process_sp, lldb::addr_t header_addr) {
@@ -108,10 +143,9 @@ size_t ObjectFileXCOFF::GetModuleSpecifications(
 
 static uint32_t XCOFFHeaderSizeFromMagic(uint32_t magic) {
   switch (magic) {
-    // TODO: 32bit not supported yet
+    // TODO: 32bit not supported.
     // case XCOFF::XCOFF32:
     //  return sizeof(struct llvm::object::XCOFFFileHeader32);
-
   case XCOFF::XCOFF64:
     return sizeof(struct llvm::object::XCOFFFileHeader64);
     break;
@@ -127,19 +161,30 @@ bool ObjectFileXCOFF::MagicBytesMatch(DataBufferSP &data_sp,
                                       lldb::addr_t data_length) {
   lldb_private::DataExtractor data;
   data.SetData(data_sp, data_offset, data_length);
+  // Need to set this as XCOFF is only compatible with Big Endian
   data.SetByteOrder(eByteOrderBig);
   lldb::offset_t offset = 0;
   uint16_t magic = data.GetU16(&offset);
   return XCOFFHeaderSizeFromMagic(magic) != 0;
 }
 
-bool ObjectFileXCOFF::ParseHeader() { return false; }
+bool ObjectFileXCOFF::ParseHeader() {
+  // Only 64-bit is supported for now
+  return m_binary->fileHeader64()->Magic == XCOFF::XCOFF64;
+}
 
 ByteOrder ObjectFileXCOFF::GetByteOrder() const { return eByteOrderBig; }
 
 bool ObjectFileXCOFF::IsExecutable() const { return true; }
 
-uint32_t ObjectFileXCOFF::GetAddressByteSize() const { return 8; }
+uint32_t ObjectFileXCOFF::GetAddressByteSize() const {
+  // 32-bit not supported. return 8 for 64-bit XCOFF::XCOFF64
+  return 8;
+}
+
+AddressClass ObjectFileXCOFF::GetAddressClass(addr_t file_addr) {
+  return AddressClass::eUnknown;
+}
 
 void ObjectFileXCOFF::ParseSymtab(Symtab &lldb_symtab) {}
 
@@ -159,7 +204,13 @@ UUID ObjectFileXCOFF::GetUUID() { return UUID(); }
 
 uint32_t ObjectFileXCOFF::GetDependentModules(FileSpecList &files) { return 0; }
 
-ObjectFile::Type ObjectFileXCOFF::CalculateType() { return eTypeExecutable; }
+ObjectFile::Type ObjectFileXCOFF::CalculateType() {
+  if (m_binary->fileHeader64()->Flags & XCOFF::F_EXEC)
+    return eTypeExecutable;
+  else if (m_binary->fileHeader64()->Flags & XCOFF::F_SHROBJ)
+    return eTypeSharedLibrary;
+  return eTypeUnknown;
+}
 
 ObjectFile::Strata ObjectFileXCOFF::CalculateStrata() { return eStrataUnknown; }
 

lldb/source/Plugins/ObjectFile/XCOFF/ObjectFileXCOFF.h

@@ -68,6 +68,8 @@ class ObjectFileXCOFF : public lldb_private::ObjectFile {
 
   uint32_t GetAddressByteSize() const override;
 
+  lldb_private::AddressClass GetAddressClass(lldb::addr_t file_addr) override;
+
   void ParseSymtab(lldb_private::Symtab &symtab) override;
 
   bool IsStripped() override;
@@ -99,6 +101,11 @@ class ObjectFileXCOFF : public lldb_private::ObjectFile {
   static lldb::WritableDataBufferSP
   MapFileDataWritable(const lldb_private::FileSpec &file, uint64_t Size,
                       uint64_t Offset);
+
+private:
+  bool CreateBinary();
+
+  std::unique_ptr<llvm::object::XCOFFObjectFile> m_binary;
 };
 
 #endif // LLDB_SOURCE_PLUGINS_OBJECTFILE_XCOFF_OBJECTFILE_H

lldb/test/Shell/ObjectFile/XCOFF/basic-info.yaml

@@ -13,7 +13,7 @@ FileHeader:
   MagicNumber:     0x1F7
   NumberOfSections: 1 
   CreationTime:    000000000
-  Flags:           0x0000
+  Flags:           0x0002
 Sections:
   - Name:            .text
     Address:         0x100000438