[llvm-lib][llvm-dlltool][Object] Add support for EXPORTAS name types. (#78772)

EXPORTAS is a new name type in import libraries. It's used by default on ARM64EC,
but it's allowed on other platforms as well.

Author: cjacek

llvm/include/llvm/BinaryFormat/COFF.h

@@ -716,7 +716,10 @@ enum ImportNameType : unsigned {
   IMPORT_NAME_NOPREFIX = 2,
   /// The import name is the public symbol name, but skipping the leading ?,
   /// @, or optionally _, and truncating at the first @.
-  IMPORT_NAME_UNDECORATE = 3
+  IMPORT_NAME_UNDECORATE = 3,
+  /// The import name is specified as a separate string in the import library
+  /// object file.
+  IMPORT_NAME_EXPORTAS = 4
 };
 
 enum class GuardFlags : uint32_t {

llvm/include/llvm/Object/COFFImportFile.h

@@ -92,6 +92,10 @@ struct COFFShortExport {
   /// file, this is "baz" in "EXPORTS\nfoo = bar == baz".
   std::string AliasTarget;
 
+  /// Specifies EXPORTAS name. In a .def file, this is "bar" in
+  /// "EXPORTS\nfoo EXPORTAS bar".
+  std::string ExportAs;
+
   uint16_t Ordinal = 0;
   bool Noname = false;
   bool Data = false;

llvm/lib/Object/COFFImportFile.cpp

@@ -71,6 +71,12 @@ StringRef COFFImportFile::getExportName() const {
     name = ltrim1(name, "?@_");
     name = name.substr(0, name.find('@'));
     break;
+  case IMPORT_NAME_EXPORTAS: {
+    // Skip DLL name
+    name = Data.getBuffer().substr(sizeof(*hdr) + name.size() + 1);
+    name = name.split('\0').second.split('\0').first;
+    break;
+  }
   default:
     break;
   }
@@ -209,6 +215,7 @@ class ObjectFactory {
   // Library Format.
   NewArchiveMember createShortImport(StringRef Sym, uint16_t Ordinal,
                                      ImportType Type, ImportNameType NameType,
+                                     StringRef ExportName,
                                      MachineTypes Machine);
 
   // Create a weak external file which is described in PE/COFF Aux Format 3.
@@ -500,12 +507,13 @@ NewArchiveMember ObjectFactory::createNullThunk(std::vector<uint8_t> &Buffer) {
   return {MemoryBufferRef{F, ImportName}};
 }
 
-NewArchiveMember ObjectFactory::createShortImport(StringRef Sym,
-                                                  uint16_t Ordinal,
-                                                  ImportType ImportType,
-                                                  ImportNameType NameType,
-                                                  MachineTypes Machine) {
+NewArchiveMember
+ObjectFactory::createShortImport(StringRef Sym, uint16_t Ordinal,
+                                 ImportType ImportType, ImportNameType NameType,
+                                 StringRef ExportName, MachineTypes Machine) {
   size_t ImpSize = ImportName.size() + Sym.size() + 2; // +2 for NULs
+  if (!ExportName.empty())
+    ImpSize += ExportName.size() + 1;
   size_t Size = sizeof(coff_import_header) + ImpSize;
   char *Buf = Alloc.Allocate<char>(Size);
   memset(Buf, 0, Size);
@@ -525,6 +533,10 @@ NewArchiveMember ObjectFactory::createShortImport(StringRef Sym,
   memcpy(P, Sym.data(), Sym.size());
   P += Sym.size() + 1;
   memcpy(P, ImportName.data(), ImportName.size());
+  if (!ExportName.empty()) {
+    P += ImportName.size() + 1;
+    memcpy(P, ExportName.data(), ExportName.size());
+  }
 
   return {MemoryBufferRef(StringRef(Buf, Size), ImportName)};
 }
@@ -641,27 +653,39 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
       ImportType = IMPORT_CONST;
 
     StringRef SymbolName = E.SymbolName.empty() ? E.Name : E.SymbolName;
-    ImportNameType NameType = E.Noname
-                                  ? IMPORT_ORDINAL
-                                  : getNameType(SymbolName, E.Name,
-                                                Machine, MinGW);
-    Expected<std::string> Name = E.ExtName.empty()
-                                     ? std::string(SymbolName)
-                                     : replace(SymbolName, E.Name, E.ExtName);
-
-    if (!Name)
-      return Name.takeError();
-
-    if (!E.AliasTarget.empty() && *Name != E.AliasTarget) {
+    std::string Name;
+
+    if (E.ExtName.empty()) {
+      Name = std::string(SymbolName);
+    } else {
+      Expected<std::string> ReplacedName =
+          replace(SymbolName, E.Name, E.ExtName);
+      if (!ReplacedName)
+        return ReplacedName.takeError();
+      Name.swap(*ReplacedName);
+    }
+
+    if (!E.AliasTarget.empty() && Name != E.AliasTarget) {
       Members.push_back(
-          OF.createWeakExternal(E.AliasTarget, *Name, false, Machine));
+          OF.createWeakExternal(E.AliasTarget, Name, false, Machine));
       Members.push_back(
-          OF.createWeakExternal(E.AliasTarget, *Name, true, Machine));
+          OF.createWeakExternal(E.AliasTarget, Name, true, Machine));
       continue;
     }
 
-    Members.push_back(
-        OF.createShortImport(*Name, E.Ordinal, ImportType, NameType, Machine));
+    ImportNameType NameType;
+    std::string ExportName;
+    if (E.Noname) {
+      NameType = IMPORT_ORDINAL;
+    } else if (!E.ExportAs.empty()) {
+      NameType = IMPORT_NAME_EXPORTAS;
+      ExportName = E.ExportAs;
+    } else {
+      NameType = getNameType(SymbolName, E.Name, Machine, MinGW);
+    }
+
+    Members.push_back(OF.createShortImport(Name, E.Ordinal, ImportType,
+                                           NameType, ExportName, Machine));
   }
 
   return writeArchive(Path, Members, SymtabWritingMode::NormalSymtab,

llvm/lib/Object/COFFModuleDefinition.cpp

@@ -39,6 +39,7 @@ enum Kind {
   KwConstant,
   KwData,
   KwExports,
+  KwExportAs,
   KwHeapsize,
   KwLibrary,
   KwName,
@@ -116,6 +117,7 @@ class Lexer {
                    .Case("CONSTANT", KwConstant)
                    .Case("DATA", KwData)
                    .Case("EXPORTS", KwExports)
+                   .Case("EXPORTAS", KwExportAs)
                    .Case("HEAPSIZE", KwHeapsize)
                    .Case("LIBRARY", KwLibrary)
                    .Case("NAME", KwName)
@@ -284,7 +286,16 @@ class Parser {
           E.AliasTarget = std::string("_").append(E.AliasTarget);
         continue;
       }
-      unget();
+      // EXPORTAS must be at the end of export definition
+      if (Tok.K == KwExportAs) {
+        read();
+        if (Tok.K == Eof)
+          return createError(
+              "unexpected end of file, EXPORTAS identifier expected");
+        E.ExportAs = std::string(Tok.Value);
+      } else {
+        unget();
+      }
       Info.Exports.push_back(E);
       return Error::success();
     }

llvm/test/tools/llvm-lib/exportas.test

@@ -0,0 +1,94 @@
+Test EXPORTAS in importlibs.
+
+RUN: split-file %s %t.dir && cd %t.dir
+RUN: llvm-lib -machine:amd64 -def:test.def -out:test.lib
+
+RUN: llvm-nm --print-armap test.lib | FileCheck --check-prefix=ARMAP %s
+
+ARMAP:      Archive map
+ARMAP-NEXT: __IMPORT_DESCRIPTOR_test in test.dll
+ARMAP-NEXT: __NULL_IMPORT_DESCRIPTOR in test.dll
+ARMAP-NEXT: __imp_func in test.dll
+ARMAP-NEXT: __imp_func2 in test.dll
+ARMAP-NEXT: __imp_func3 in test.dll
+ARMAP-NEXT: __imp_mydata in test.dll
+ARMAP-NEXT: func in test.dll
+ARMAP-NEXT: func2 in test.dll
+ARMAP-NEXT: func3 in test.dll
+ARMAP-NEXT: test_NULL_THUNK_DATA in test.dll
+
+RUN: llvm-readobj test.lib | FileCheck --check-prefix=READOBJ %s
+
+READOBJ:      File: test.lib(test.dll)
+READOBJ-NEXT: Format: COFF-x86-64
+READOBJ-NEXT: Arch: x86_64
+READOBJ-NEXT: AddressSize: 64bit
+READOBJ-EMPTY:
+READOBJ-NEXT: File: test.lib(test.dll)
+READOBJ-NEXT: Format: COFF-x86-64
+READOBJ-NEXT: Arch: x86_64
+READOBJ-NEXT: AddressSize: 64bit
+READOBJ-EMPTY:
+READOBJ-NEXT: File: test.lib(test.dll)
+READOBJ-NEXT: Format: COFF-x86-64
+READOBJ-NEXT: Arch: x86_64
+READOBJ-NEXT: AddressSize: 64bit
+READOBJ-EMPTY:
+READOBJ-NEXT: File: test.dll
+READOBJ-NEXT: Format: COFF-import-file-x86-64
+READOBJ-NEXT: Type: code
+READOBJ-NEXT: Name type: export as
+READOBJ-NEXT: Export name: expfunc
+READOBJ-NEXT: Symbol: __imp_func
+READOBJ-NEXT: Symbol: func
+READOBJ-EMPTY:
+READOBJ-NEXT: File: test.dll
+READOBJ-NEXT: Format: COFF-import-file-x86-64
+READOBJ-NEXT: Type: data
+READOBJ-NEXT: Name type: export as
+READOBJ-NEXT: Export name: expdata
+READOBJ-NEXT: Symbol: __imp_mydata
+READOBJ-EMPTY:
+READOBJ-NEXT: File: test.dll
+READOBJ-NEXT: Format: COFF-import-file-x86-64
+READOBJ-NEXT: Type: code
+READOBJ-NEXT: Name type: export as
+READOBJ-NEXT: Export name: expfunc2
+READOBJ-NEXT: Symbol: __imp_func2
+READOBJ-NEXT: Symbol: func2
+READOBJ-EMPTY:
+READOBJ-NEXT: File: test.dll
+READOBJ-NEXT: Format: COFF-import-file-x86-64
+READOBJ-NEXT: Type: code
+READOBJ-NEXT: Name type: export as
+READOBJ-NEXT: Export name: expfunc3
+READOBJ-NEXT: Symbol: __imp_func3
+READOBJ-NEXT: Symbol: func3
+
+
+EXPORTAS must be at the end of entry declaration.
+RUN: not llvm-lib -machine:amd64 -def:test2.def -out:test2.lib 2>&1 \
+RUN:              | FileCheck --check-prefix=ERROR %s
+RUN: not llvm-lib -machine:amd64 -def:test3.def -out:test3.lib 2>&1 \
+RUN:              | FileCheck --check-prefix=ERROR %s
+ERROR: Invalid data was encountered while parsing the file
+
+
+#--- test.def
+LIBRARY test.dll
+EXPORTS
+        func EXPORTAS expfunc
+        mydata DATA EXPORTAS expdata
+        func2 = myfunc2 EXPORTAS expfunc2
+        func3 = otherdll.otherfunc3 EXPORTAS expfunc3
+
+#--- test2.def
+LIBRARY test.dll
+EXPORTS
+        func EXPORTAS expfunc
+        mydata EXPORTAS expdata DATA
+
+#--- test3.def
+LIBRARY test.dll
+EXPORTS
+        mydata EXPORTAS

llvm/tools/llvm-readobj/COFFImportDumper.cpp

@@ -45,6 +45,9 @@ void dumpCOFFImportFile(const COFFImportFile *File, ScopedPrinter &Writer) {
   case COFF::IMPORT_NAME_UNDECORATE:
     Writer.printString("Name type", "undecorate");
     break;
+  case COFF::IMPORT_NAME_EXPORTAS:
+    Writer.printString("Name type", "export as");
+    break;
   }
 
   if (H->getNameType() != COFF::IMPORT_ORDINAL)