[COFF] Add SymbolName as a distinct field in COFFImportFile

[mstorsjo]

Summary

The previous Name and ExtName aren't enough to convey all the nuances between weak aliases and stdcall decorated function names.

A test for this will be added in LLD.

[rnk]

lib/Object/COFFImportFile.cpp

593 ↗

(On Diff #110458)

Do we not need to look at ExtName for weak symbols?

[mstorsjo]

lib/Object/COFFImportFile.cpp

593 ↗

(On Diff #110458)

If E.isWeak(), we created a weak external above and never even get here (extend the diff by some lines above to see more context). So E.isWeak() could never be true here before.

This brings it back to more or less exact the same logic that was used before this was split out of LLD.

[mstorsjo]

lib/Object/COFFImportFile.cpp

582 ↗

(On Diff #110458)

Should we extend isWeak() to check SymbolName instead of Name, if set? Or just avoid touching the decoration altogether in llvm-dlltool D36548 if we want to create a weak alias?

[mstorsjo]

Instead of this patch, we could also update getNameType to check for decoration, e.g like this:

if (!Sym.startswith("?") && Sym.find('@', 1) != Sym.npos)
  return IMPORT_NAME_UNDECORATE;

This patch tries to get things back to match how things were in lld prior to factorizing it, while the snippet above takes it into a different direction. I'd appreciate if @ruiu could chime in on which direction is better to take here.

[ruiu]

LGTM

llvm/trunk/include/llvm/Object/COFFImportFile.h

private:
   bool isData() const {
     return getCOFFImportHeader()->getType() == COFF::IMPORT_DATA;
   }
 };
 
 struct COFFShortExport {
   std::string Name;
   std::string ExtName;
+  std::string SymbolName;
 
   uint16_t Ordinal = 0;
   bool Noname = false;
   bool Data = false;
   bool Private = false;
   bool Constant = false;
 
   bool isWeak() {

llvm/trunk/lib/Object/COFFImportFile.cpp

for (COFFShortExport E : Exports) {
     }
 
     ImportType ImportType = IMPORT_CODE;
     if (E.Data)
       ImportType = IMPORT_DATA;
     if (E.Constant)
       ImportType = IMPORT_CONST;
 
-    StringRef SymbolName = E.isWeak() ? E.ExtName : E.Name;
+    StringRef SymbolName = E.SymbolName.empty() ? E.Name : E.SymbolName;
     ImportNameType NameType = getNameType(SymbolName, E.Name, Machine);
     Expected<std::string> Name = E.ExtName.empty()
                                      ? SymbolName
                                      : replace(SymbolName, E.Name, E.ExtName);
 
     if (!Name) {
       return errorToErrorCode(Name.takeError());
     }