[llvm-dlltool] Handle import renaming using other name types, when po…

…ssible This avoids needing to use weak aliases for these cases. (Weak aliases only work if there's another, regular import entry that provide the desired symbol from the DLL.)
llvm · Jul 16, 2024 · 0fad0b9 · 0fad0b9
1 parent 80e18b9
commit 0fad0b9
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Showing 2 changed files with 61 additions and 21 deletions.
diff --git a/llvm/lib/Object/COFFImportFile.cpp b/llvm/lib/Object/COFFImportFile.cpp
@@ -52,25 +52,37 @@ StringRef COFFImportFile::getFileFormatName() const {
   }
 }
 
-StringRef COFFImportFile::getExportName() const {
-  const coff_import_header *hdr = getCOFFImportHeader();
-  StringRef name = Data.getBuffer().substr(sizeof(*hdr)).split('\0').first;
-
+static StringRef applyNameType(ImportNameType Type, StringRef name) {
   auto ltrim1 = [](StringRef s, StringRef chars) {
     return !s.empty() && chars.contains(s[0]) ? s.substr(1) : s;
   };
 
-  switch (hdr->getNameType()) {
-  case IMPORT_ORDINAL:
-    name = "";
-    break;
+  switch (Type) {
   case IMPORT_NAME_NOPREFIX:
     name = ltrim1(name, "?@_");
     break;
   case IMPORT_NAME_UNDECORATE:
     name = ltrim1(name, "?@_");
     name = name.substr(0, name.find('@'));
     break;
+  default:
+    break;
+  }
+  return name;
+}
+
+StringRef COFFImportFile::getExportName() const {
+  const coff_import_header *hdr = getCOFFImportHeader();
+  StringRef name = Data.getBuffer().substr(sizeof(*hdr)).split('\0').first;
+
+  switch (hdr->getNameType()) {
+  case IMPORT_ORDINAL:
+    name = "";
+    break;
+  case IMPORT_NAME_NOPREFIX:
+  case IMPORT_NAME_UNDECORATE:
+    name = applyNameType(static_cast<ImportNameType>(hdr->getNameType()), name);
+    break;
   case IMPORT_NAME_EXPORTAS: {
     // Skip DLL name
     name = Data.getBuffer().substr(sizeof(*hdr) + name.size() + 1);
@@ -691,26 +703,38 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
         Name.swap(*ReplacedName);
       }
 
-      if (!E.ImportName.empty() && Name != E.ImportName) {
-        StringRef Prefix = "";
-        if (Machine == IMAGE_FILE_MACHINE_I386 && AddUnderscores)
-          Prefix = "_";
-
-        if (ImportType == IMPORT_CODE)
-          Members.push_back(OF.createWeakExternal((Prefix + E.ImportName).str(),
-                                                  Name, false, M));
-        Members.push_back(OF.createWeakExternal((Prefix + E.ImportName).str(),
-                                                Name, true, M));
-        continue;
-      }
-
       ImportNameType NameType;
       std::string ExportName;
       if (E.Noname) {
         NameType = IMPORT_ORDINAL;
       } else if (!E.ExportAs.empty()) {
         NameType = IMPORT_NAME_EXPORTAS;
         ExportName = E.ExportAs;
+      } else if (!E.ImportName.empty()) {
+        // If we need to import from a specific ImportName, we may need to use
+        // a weak alias (which needs another import to point at). But if we can
+        // express ImportName based on the symbol name and a specific NameType,
+        // prefer that over an alias.
+        if (Machine == IMAGE_FILE_MACHINE_I386 &&
+            applyNameType(IMPORT_NAME_UNDECORATE, Name) == E.ImportName)
+          NameType = IMPORT_NAME_UNDECORATE;
+        else if (Machine == IMAGE_FILE_MACHINE_I386 &&
+                 applyNameType(IMPORT_NAME_NOPREFIX, Name) == E.ImportName)
+          NameType = IMPORT_NAME_NOPREFIX;
+        else if (Name == E.ImportName)
+          NameType = IMPORT_NAME;
+        else {
+          StringRef Prefix = "";
+          if (Machine == IMAGE_FILE_MACHINE_I386 && AddUnderscores)
+            Prefix = "_";
+
+          if (ImportType == IMPORT_CODE)
+            Members.push_back(OF.createWeakExternal(
+                (Prefix + E.ImportName).str(), Name, false, M));
+          Members.push_back(OF.createWeakExternal((Prefix + E.ImportName).str(),
+                                                  Name, true, M));
+          continue;
+        }
       } else {
         NameType = getNameType(SymbolName, E.Name, M, MinGW);
       }

diff --git a/llvm/test/tools/llvm-dlltool/coff-decorated.def b/llvm/test/tools/llvm-dlltool/coff-decorated.def
@@ -13,6 +13,10 @@ StdcallExportName@4=StdcallInternalFunction@4
 OtherStdcallExportName@4=CdeclInternalFunction
 CdeclExportName=StdcallInternalFunction@4
 
+NoprefixStdcall@4 == NoprefixStdcall@4
+DecoratedStdcall@4 == _DecoratedStdcall@4
+UndecoratedStdcall@4 == UndecoratedStdcall
+
 ; CHECK:      Name type: noprefix
 ; CHECK-NEXT: Export name: CdeclFunction
 ; CHECK-NEXT: Symbol: __imp__CdeclFunction
@@ -43,3 +47,15 @@ CdeclExportName=StdcallInternalFunction@4
 ; CHECK-NEXT: Export name: CdeclExportName
 ; CHECK-NEXT: Symbol: __imp__CdeclExportName
 ; CHECK-NEXT: Symbol: _CdeclExportName
+; CHECK:      Name type: noprefix
+; CHECK-NEXT: Export name: NoprefixStdcall@4
+; CHECK-NEXT: Symbol: __imp__NoprefixStdcall@4
+; CHECK-NEXT: Symbol: _NoprefixStdcall@4
+; CHECK:      Name type: name
+; CHECK-NEXT: Export name: _DecoratedStdcall@4
+; CHECK-NEXT: Symbol: __imp__DecoratedStdcall@4
+; CHECK-NEXT: Symbol: _DecoratedStdcall@4
+; CHECK:      Name type: undecorate
+; CHECK-NEXT: Export name: UndecoratedStdcall
+; CHECK-NEXT: Symbol: __imp__UndecoratedStdcall@4
+; CHECK-NEXT: Symbol: _UndecoratedStdcall@4