[llvm-readobj][COFF] Print forwarder export symbols correctly

[mstorsjo]

LGTM, this looks reasonable to me!

llvm/test/tools/llvm-readobj/COFF/exports-forwarder.yaml

13

Nitpick, I think you could achieve the same here without -lldmingw, allowing you to lose -exclude-all-symbols too - and that would shrink the rdata by a couple bytes too.

(Mingw executables get a couple extra dummy bytes due to ctor/dtor list placeholders, see insertCtorDtorSymbols in Writer.cpp. In theory those placeholders could be symbols without any associated dummy data, but changing it would need to be synchronized across binutils/lld/mingw-w64-crt and would break mixing versions among all those.)

[alvinhochun]

Reduce size of test file

[mstorsjo]

In D134528#3811387, @alvinhochun wrote:

Reduce size of test file

Awesome, thanks!

llvm/test/tools/llvm-readobj/COFF/exports-forwarder.yaml

+# RUN: yaml2obj %s -o %t
+# RUN: llvm-readobj --coff-exports %t | FileCheck %s
+
+# CHECK:      Export {
+# CHECK-NEXT:   Ordinal: 1
+# CHECK-NEXT:   Name: LoadLibrary
+# CHECK-NEXT:   ForwardedTo: kernel32.LoadLibrary
+# CHECK-NEXT: }
+
+# Test file generated with:
+#   clang -O2 --target=x86_64-windows-msvc test.c -nostdlib -c -o test.obj
+#   lld-link -dll -out:test.dll -entry:entry -export:LoadLibrary=kernel32.LoadLibrary test.obj
+# test.c:
+#   void entry(void) {}
+
+--- !COFF
+OptionalHeader:
+  AddressOfEntryPoint: 4096
+  ImageBase:       6442450944
+  SectionAlignment: 4096
+  FileAlignment:   512
+  MajorOperatingSystemVersion: 6
+  MinorOperatingSystemVersion: 0
+  MajorImageVersion: 0
+  MinorImageVersion: 0
+  MajorSubsystemVersion: 6
+  MinorSubsystemVersion: 0
+  Subsystem:       IMAGE_SUBSYSTEM_WINDOWS_GUI
+  DLLCharacteristics: [ IMAGE_DLL_CHARACTERISTICS_HIGH_ENTROPY_VA, IMAGE_DLL_CHARACTERISTICS_DYNAMIC_BASE, IMAGE_DLL_CHARACTERISTICS_NX_COMPAT ]
+  SizeOfStackReserve: 1048576
+  SizeOfStackCommit: 4096
+  SizeOfHeapReserve: 1048576
+  SizeOfHeapCommit: 4096
+  ExportTable:
+    RelativeVirtualAddress: 8192
+    Size:            110
+header:
+  Machine:         IMAGE_FILE_MACHINE_AMD64
+  Characteristics: [ IMAGE_FILE_EXECUTABLE_IMAGE, IMAGE_FILE_LARGE_ADDRESS_AWARE, IMAGE_FILE_DLL ]
+sections:
+  - Name:            .text
+    Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  4096
+    VirtualSize:     1
+    SectionData:     C3
+  - Name:            .rdata
+    Characteristics: [ IMAGE_SCN_CNT_INITIALIZED_DATA, IMAGE_SCN_MEM_READ ]
+    VirtualAddress:  8192
+    VirtualSize:     110
+    SectionData:     0000000000000000000000002820000001000000010000000100000043200000472000004B2000006578706F72742D666F727761726465722E632E746D702E646C6C00592000004D20000000004C6F61644C696272617279006B65726E656C33322E4C6F61644C69627261727900
+symbols:         []
+...

llvm/tools/llvm-readobj/COFFDumper.cpp

void COFFDumper::printCOFFImports() {
   }
 }
 
 void COFFDumper::printCOFFExports() {
   for (const ExportDirectoryEntryRef &Exp : Obj->export_directories()) {
     DictScope Export(W, "Export");
 
     StringRef Name;
-    uint32_t Ordinal, RVA;
+    uint32_t Ordinal;
+    bool IsForwarder;
 
     if (Error E = Exp.getSymbolName(Name))
       reportError(std::move(E), Obj->getFileName());
     if (Error E = Exp.getOrdinal(Ordinal))
       reportError(std::move(E), Obj->getFileName());
-    if (Error E = Exp.getExportRVA(RVA))
+    if (Error E = Exp.isForwarder(IsForwarder))
       reportError(std::move(E), Obj->getFileName());
 
     W.printNumber("Ordinal", Ordinal);
     W.printString("Name", Name);
+    StringRef ForwardTo;
+    if (IsForwarder) {
+      if (Error E = Exp.getForwardTo(ForwardTo))
+        reportError(std::move(E), Obj->getFileName());
+      W.printString("ForwardedTo", ForwardTo);
+    } else {
+      uint32_t RVA;
+      if (Error E = Exp.getExportRVA(RVA))
+        reportError(std::move(E), Obj->getFileName());
       W.printHex("RVA", RVA);
     }
   }
+}
 
 void COFFDumper::printCOFFDirectives() {
   for (const SectionRef &Section : Obj->sections()) {
     StringRef Name = unwrapOrError(Obj->getFileName(), Section.getName());
     if (Name != ".drectve")
       continue;
 
     StringRef Contents =