[COFF] Improve correctness of def parsing for GNU features

The operator == used for exporting a function with a different
name in the DLL compared to the name in the import library
(which is useful for adding linker level aliases for function
in the import library) is a feature distinct and different from
the operator = used for exporting a function with a different
name (both in import library and DLL) than in the implementation
producing the DLL.

When creating an import library using dlltool, from a def file that
contains forwards (Func = OtherDll.Func), this shouldn't affect the
produced import library, which should still behave just as if it
was a normal exported function.

This clears a lot of confusion and subtle misunderstandings, and
avoids a parameter that was used to avoid creating weak aliases
when invoked from lld. (This parameter was added previously due to
the existing conflation of the two features.)

Differential Revision: https://reviews.llvm.org/D46245

llvm-svn: 331859

2 files changed, 18 insertions, 10 deletions

diff --git a/llvm/lib/Object/COFFImportFile.cpp b/llvm/lib/Object/COFFImportFile.cpp
index c249a6d97b4..4bde1db3078 100644
--- a/llvm/lib/Object/COFFImportFile.cpp
+++ b/llvm/lib/Object/COFFImportFile.cpp
@@ -566,8 +566,7 @@ NewArchiveMember ObjectFactory::createWeakExternal(StringRef Sym,
 
 Error writeImportLibrary(StringRef ImportName, StringRef Path,
                          ArrayRef<COFFShortExport> Exports,
-                         MachineTypes Machine, bool MakeWeakAliases,
-                         bool MinGW) {
+                         MachineTypes Machine, bool MinGW) {
 
   std::vector<NewArchiveMember> Members;
   ObjectFactory OF(llvm::sys::path::filename(ImportName), Machine);
@@ -585,12 +584,6 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
     if (E.Private)
       continue;
 
-    if (E.isWeak() && MakeWeakAliases) {
-      Members.push_back(OF.createWeakExternal(E.Name, E.ExtName, false));
-      Members.push_back(OF.createWeakExternal(E.Name, E.ExtName, true));
-      continue;
-    }
-
     ImportType ImportType = IMPORT_CODE;
     if (E.Data)
       ImportType = IMPORT_DATA;
@@ -606,6 +599,12 @@ Error writeImportLibrary(StringRef ImportName, StringRef Path,
     if (!Name)
       return Name.takeError();
 
+    if (!E.AliasTarget.empty() && *Name != E.AliasTarget) {
+      Members.push_back(OF.createWeakExternal(E.AliasTarget, *Name, false));
+      Members.push_back(OF.createWeakExternal(E.AliasTarget, *Name, true));
+      continue;
+    }
+
     Members.push_back(
         OF.createShortImport(*Name, E.Ordinal, ImportType, NameType));
   }
diff --git a/llvm/lib/Object/COFFModuleDefinition.cpp b/llvm/lib/Object/COFFModuleDefinition.cpp
index a571354648d..c703071b86e 100644
--- a/llvm/lib/Object/COFFModuleDefinition.cpp
+++ b/llvm/lib/Object/COFFModuleDefinition.cpp
@@ -37,6 +37,7 @@ enum Kind {
   Identifier,
   Comma,
   Equal,
+  EqualEqual,
   KwBase,
   KwConstant,
   KwData,
@@ -104,9 +105,10 @@ public:
     }
     case '=':
       Buf = Buf.drop_front();
-      // GNU dlltool accepts both = and ==.
-      if (Buf.startswith("="))
+      if (Buf.startswith("=")) {
         Buf = Buf.drop_front();
+        return Token(EqualEqual, "==");
+      }
       return Token(Equal, "=");
     case ',':
       Buf = Buf.drop_front();
@@ -282,6 +284,13 @@ private:
         E.Private = true;
         continue;
       }
+      if (Tok.K == EqualEqual) {
+        read();
+        E.AliasTarget = Tok.Value;
+        if (Machine == IMAGE_FILE_MACHINE_I386 && !isDecorated(E.AliasTarget, MingwDef))
+          E.AliasTarget = std::string("_").append(E.AliasTarget);
+        continue;
+      }
       unget();
       Info.Exports.push_back(E);
       return Error::success();