[llvm/Object] - Make dyn_cast<XCOFFObjectFile> work as it should.

[grimar]

Summary

Currently, dyn_cast<XCOFFObjectFile> always does cast and returns a pointer,
even when we pass ELF/Wasm/Mach-O or COFF instead of XCOFF.

It happens because XCOFFObjectFile class does not implement classof.
I've fixed it and added a unit test.

[MaskRay]

llvm/tools/llvm-objdump/llvm-objdump.cpp

540 ↗

(On Diff #287667)

This reordering is unneeded...

[grimar]

llvm/tools/llvm-objdump/llvm-objdump.cpp

540 ↗

(On Diff #287667)

Yes, I've did it to test the change mostly. I'll try to prepare a unit test instead.

[grimar]

• Added unit test.

[jhenderson]

LGTM.

llvm/include/llvm/Object/XCOFFObjectFile.h

public:
   void checkSymbolEntryPointer(uintptr_t SymbolEntPtr) const;
 
   // Relocation-related interfaces.
   Expected<uint32_t>
   getLogicalNumberOfRelocationEntries(const XCOFFSectionHeader32 &Sec) const;
 
   Expected<ArrayRef<XCOFFRelocation32>>
   relocations(const XCOFFSectionHeader32 &) const;
+
+  static bool classof(const Binary *B) { return B->isXCOFF(); }
 }; // XCOFFObjectFile
 
 class XCOFFSymbolRef {
   const DataRefImpl SymEntDataRef;
   const XCOFFObjectFile *const OwningObjectPtr;
 
 public:
   XCOFFSymbolRef(DataRefImpl SymEntDataRef,

llvm/unittests/Object/XCOFFObjectFileTest.cpp

 //===- XCOFFObjectFileTest.cpp - Tests for XCOFFObjectFile ----------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/Object/ELFObjectFile.h"
 #include "llvm/Object/XCOFFObjectFile.h"
 #include "llvm/Testing/Support/Error.h"
 #include "gtest/gtest.h"
 
 using namespace llvm;
 using namespace llvm::object;
 
+TEST(XCOFFObjectFileTest, XCOFFObjectType) {
+  // Create an arbitrary object of a non-XCOFF type and test that
+  // dyn_cast<XCOFFObjectFile> returns null for it.
+  char Buf[sizeof(typename ELF64LE::Ehdr)] = {};
+  memcpy(Buf, "\177ELF", 4);
+
+  auto *EHdr = reinterpret_cast<typename ELF64LE::Ehdr *>(Buf);
+  EHdr->e_ident[llvm::ELF::EI_CLASS] = llvm::ELF::ELFCLASS64;
+  EHdr->e_ident[llvm::ELF::EI_DATA] = llvm::ELF::ELFDATA2LSB;
+
+  MemoryBufferRef Source(StringRef(Buf, sizeof(Buf)), "non-XCOFF");
+  Expected<std::unique_ptr<ObjectFile>> ObjOrErr =
+      ObjectFile::createObjectFile(Source);
+  ASSERT_THAT_EXPECTED(ObjOrErr, Succeeded());
+
+  EXPECT_TRUE(dyn_cast<XCOFFObjectFile>((*ObjOrErr).get()) == nullptr);
+}
+
 TEST(XCOFFObjectFileTest, doesXCOFFTracebackTableBegin) {
   EXPECT_TRUE(doesXCOFFTracebackTableBegin({0, 0, 0, 0}));
   EXPECT_TRUE(doesXCOFFTracebackTableBegin({0, 0, 0, 0, 1}));
   EXPECT_FALSE(doesXCOFFTracebackTableBegin({0, 0, 0, 1}));
   EXPECT_FALSE(doesXCOFFTracebackTableBegin({0, 0, 0}));
 }
 
 TEST(XCOFFObjectFileTest, XCOFFTracebackTableAPIGeneral) {