[llvm-dlltool] Handle external and internal names with differing decoration

[mstorsjo]

Summary

Also add a missed part of the test from SVN r369747.

I tried looking at GNU ld/dlltool's behaviour wrt decoration, with and without the --kill-at option, and it turned out that lld mostly matched GNU ld's behaviour already (including the surprising case where GNU ld's --kill-at also removes the decoration from the import lib symbol, contrary to what GNU dlltool does). So the main mismatch was in how llvm-dlltool handled these case, and I chose the easy way out; just ignore all variants of "ExtName = Name" and make it behave as if only "ExtName" was specified, which is the only aspect that matters when generating an import library.

@jacek I saw that the patch already landed in wine for stopping including the alias part in the generated def files, but with that reverted, would it work with llvm-dlltool with this patch?

[jacek]

Yes, it works with your patch and Wine workaround reverted.

[mstorsjo]

In D66996#1652450, @jacek wrote:

Yes, it works with your patch and Wine workaround reverted.

Great, thanks for testing!

[ruiu]

LGTM

llvm/trunk/lib/ToolDrivers/llvm-dlltool/DlltoolDriver.cpp

int llvm::dlltoolDriverMain(llvm::ArrayRef<const char *> ArgsArr) {
 
   if (Def->OutputFile.empty()) {
     llvm::errs() << "no DLL name specified\n";
     return 1;
   }
 
   std::string Path = Args.getLastArgValue(OPT_l);
 
+  // If ExtName is set (if the "ExtName = Name" syntax was used), overwrite
+  // Name with ExtName and clear ExtName. When only creating an import
+  // library and not linking, the internal name is irrelevant. This avoids
+  // cases where writeImportLibrary tries to transplant decoration from
+  // symbol decoration onto ExtName.
+  for (COFFShortExport& E : Def->Exports) {
+    if (!E.ExtName.empty()) {
+      E.Name = E.ExtName;
+      E.ExtName.clear();
+    }
+  }
+
   if (Machine == IMAGE_FILE_MACHINE_I386 && Args.getLastArg(OPT_k)) {
     for (COFFShortExport& E : Def->Exports) {
       if (!E.AliasTarget.empty() || (!E.Name.empty() && E.Name[0] == '?'))
         continue;
       E.SymbolName = E.Name;
       // Trim off the trailing decoration. Symbols will always have a
       // starting prefix here (either _ for cdecl/stdcall, @ for fastcall
       // or ? for C++ functions). Vectorcall functions won't have any
       // fixed prefix, but the function base name will still be at least
       // one char.
       E.Name = E.Name.substr(0, E.Name.find('@', 1));
       // By making sure E.SymbolName != E.Name for decorated symbols,
       // writeImportLibrary writes these symbols with the type
       // IMPORT_NAME_UNDECORATE.
-      E.ExtName = E.ExtName.substr(0, E.ExtName.find('@', 1));
     }
   }
 
   if (!Path.empty() &&
       writeImportLibrary(Def->OutputFile, Path, Def->Exports, Machine, true))
     return 1;
   return 0;
 }

llvm/trunk/test/tools/llvm-dlltool/coff-decorated.def

 ; RUN: llvm-dlltool -k -m i386 --input-def %s --output-lib %t.a
 ; RUN: llvm-readobj %t.a | FileCheck %s
 ; RUN: llvm-nm %t.a | FileCheck %s -check-prefix=CHECK-NM
 
 LIBRARY test.dll
 EXPORTS
 CdeclFunction
 StdcallFunction@4
 @FastcallFunction@4
 StdcallAlias@4==StdcallFunction@4
 ??_7exception@@6B@
 StdcallExportName@4=StdcallInternalFunction@4
+OtherStdcallExportName@4=CdeclInternalFunction
+CdeclExportName=StdcallInternalFunction@4
 
 ; CHECK: Name type: noprefix
 ; CHECK: Symbol: __imp__CdeclFunction
 ; CHECK: Symbol: _CdeclFunction
 ; CHECK: Name type: undecorate
 ; CHECK: Symbol: __imp__StdcallFunction@4
 ; CHECK: Symbol: _StdcallFunction@4
 ; CHECK: Name type: undecorate
 ; CHECK: Symbol: __imp_@FastcallFunction@4
 ; CHECK: Symbol: @FastcallFunction@4
 ; CHECK: Name type: name
 ; CHECK: Symbol: __imp_??_7exception@@6B@
 ; CHECK: Symbol: ??_7exception@@6B@
 ; CHECK-NM: W _StdcallAlias@4
 ; CHECK-NM: U _StdcallFunction@4
+; CHECK: Name type: undecorate
 ; CHECK: Symbol: __imp__StdcallExportName@4{{$}}
 ; CHECK: Symbol: _StdcallExportName@4{{$}}
+; CHECK: Name type: undecorate
+; CHECK: Symbol: __imp__OtherStdcallExportName@4{{$}}
+; CHECK: Symbol: _OtherStdcallExportName@4{{$}}
+; CHECK: Name type: noprefix
+; CHECK: Symbol: __imp__CdeclExportName
+; CHECK: Symbol: _CdeclExportName