[PECOFF] Fix /entry option.

This is yet another edge case of ambiguous name resolution.
When a symbol is specified with /entry:SYM, SYM may be resolved
to the C++ mangled function name (?SYM@@YAXXZ).

llvm-svn: 218706

lld/lib/ReaderWriter/PECOFF/LinkerGeneratedSymbolFile.h

@@ -298,7 +298,7 @@ private:
     _firstTime = false;
 
     if (_ctx->hasEntry()) {
-      StringRef entrySym = _ctx->allocate(_ctx->decorateSymbol(getEntry()));
+      StringRef entrySym = _ctx->allocate(getEntry());
       _undefinedAtoms._atoms.push_back(
           new (_alloc) SimpleUndefinedAtom(*this, entrySym));
       _ctx->setHasEntry(true);
@@ -313,9 +313,16 @@ private:
   // subsystem if it's unknown.
   std::string getEntry() const {
     StringRef opt = _ctx->getEntrySymbolName();
-    if (!opt.empty())
-      return opt;
+    if (!opt.empty()) {
+      std::string mangled;
+      if (findDecoratedSymbol(_ctx, _syms.get(), opt, mangled))
+        return mangled;
+      return _ctx->decorateSymbol(opt);
+    }
+    return _ctx->decorateSymbol(getDefaultEntry());
+  }
 
+  std::string getDefaultEntry() const {
     const std::string wWinMainCRTStartup = "wWinMainCRTStartup";
     const std::string WinMainCRTStartup = "WinMainCRTStartup";
     const std::string wmainCRTStartup = "wmainCRTStartup";

lld/test/pecoff/Inputs/entry.obj.yaml

@@ -30,4 +30,11 @@ symbols:
     SimpleType:      IMAGE_SYM_TYPE_NULL
     ComplexType:     IMAGE_SYM_DTYPE_NULL
     StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
+
+  - Name:            "?baz@@YAXXZ"
+    Value:           4
+    SectionNumber:   1
+    SimpleType:      IMAGE_SYM_TYPE_NULL
+    ComplexType:     IMAGE_SYM_DTYPE_NULL
+    StorageClass:    IMAGE_SYM_CLASS_EXTERNAL
 ...

lld/test/pecoff/entry.test

@@ -31,3 +31,8 @@ WWINMAIN: _wWinMainCRTStartup
 # RUN: llvm-readobj -file-headers %t.exe | FileCheck -check-prefix=MAINADDR %s
 
 MAINADDR: AddressOfEntryPoint: 0x1004
+
+# RUN: lld -flavor link /out:%t.exe /subsystem:console /entry:baz -- %t.obj
+# RUN: llvm-readobj -file-headers %t.exe | FileCheck -check-prefix=MANGLE %s
+
+MANGLE: AddressOfEntryPoint: 0x1004