[LLD] [MinGW] Support dllexport on i386

[mstorsjo]

Summary

In MinGW configurations (GCC, or clang with a *-windows-gnu target), the -export directives in the object file contains the undecorated symbol name, while it is decorated in MSVC configurations. (On the command line, link.exe takes an undecorated symbol name for the -export argument though.)

[ruiu]

COFF/Driver.cpp

237–242

This is pretty hairy rule, but yeah, this is probably unavoidable.

728

Since it is an internal flag, I'd like to name this /lldmingw.

COFF/Options.td

107

We don't want to show a help message for an internal flag.

[mstorsjo]

COFF/Driver.cpp

237–242

Yeah; this is the same logic as in the main handling of OPT_export on the command line though, modulo the extra && Config->MinGW.

728

Ok, will change.

COFF/Options.td

107

Removed

[mstorsjo]

Renamed the internal option to -lldmingw and removed the help text.

[ruiu]

COFF/Config.h

176

Remove the blank line.

MinGW/Driver.cpp

123

Can you add a test for this to test/MinGW/driver.test?

COFF/Config.h

struct Configuration {
   uint32_t MinorOSVersion = 0;
   bool DynamicBase = true;
   bool NxCompat = true;
   bool AllowIsolation = true;
   bool TerminalServerAware = true;
   bool LargeAddressAware = false;
   bool HighEntropyVA = false;
   bool AppContainer = false;
+
+  bool MinGW = false;
 };
 
 extern Configuration *Config;
 
 } // namespace coff
 } // namespace lld
 
 #endif

COFF/Driver.cpp

case OPT_alternatename:
       parseAlternateName(Arg->getValue());
       break;
     case OPT_defaultlib:
       if (Optional<StringRef> Path = findLib(Arg->getValue()))
         enqueuePath(*Path, false);
       break;
     case OPT_export: {
       Export E = parseExport(Arg->getValue());
+      if (Config->Machine == I386 && Config->MinGW) {
+        if (!isDecorated(E.Name))
+          E.Name = Saver.save("_" + E.Name);
+        if (!E.ExtName.empty() && !isDecorated(E.ExtName))
+          E.ExtName = Saver.save("_" + E.ExtName);
+      }
       E.Directives = true;
       Config->Exports.push_back(E);
       break;
     }
     case OPT_failifmismatch:
       checkFailIfMismatch(Arg->getValue());
       break;
     case OPT_incl:
void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   }
 
   // Handle /help
   if (Args.hasArg(OPT_help)) {
     printHelp(ArgsArr[0]);
     return;
   }
 
+  // Handle /mingw early, since it can potentially affect how other
+  // options are handled.
+  Config->MinGW = Args.hasArg(OPT_mingw);
+
   if (auto *Arg = Args.getLastArg(OPT_linkrepro)) {
     SmallString<64> Path = StringRef(Arg->getValue());
     sys::path::append(Path, "repro.tar");
 
     Expected<std::unique_ptr<TarWriter>> ErrOrWriter =
         TarWriter::create(Path, "repro");
 
     if (ErrOrWriter) {

COFF/Options.td

 defm tsaware  : B<"tsaware", "Create non-Terminal Server aware executable">;
 
 def help : F<"help">;
 def help_q : Flag<["/?", "-?"], "">, Alias<help>;
 
 // LLD extensions
 def nopdb : F<"nopdb">, HelpText<"Disable PDB generation for DWARF users">;
 def nosymtab : F<"nosymtab">;
+def mingw : F<"mingw">, HelpText<"Switch to MinGW behaviour where necessary">;
 def msvclto : F<"msvclto">;
 def rsp_quoting : Joined<["--"], "rsp-quoting=">,
   HelpText<"Quoting style for response files, 'windows' (default) or 'posix'">;
 
 // Flags for debugging
 def lldmap : F<"lldmap">;
 def lldmap_file : Joined<["/", "-"], "lldmap:">;
 

MinGW/Driver.cpp

 bool mingw::link(ArrayRef<const char *> ArgsArr, raw_ostream &Diag) {
   MinGWOptTable Parser;
   opt::InputArgList Args = Parser.parse(ArgsArr.slice(1));
 
   std::vector<std::string> LinkArgs;
   auto Add = [&](const Twine &S) { LinkArgs.push_back(S.str()); };
 
   Add("lld-link");
+  Add("-mingw");
 
   if (auto *A = Args.getLastArg(OPT_entry)) {
     StringRef S = A->getValue();
     if (Args.getLastArgValue(OPT_m) == "i386pe" && S.startswith("_"))
       Add("-entry:" + S.substr(1));
     else
       Add("-entry:" + S);
   }

test/COFF/dllexport-gnu.s

+# REQEUIRES: x86
+
+# RUN: llvm-mc -triple=i686-windows-gnu %s -filetype=obj -o %t.obj
+
+# RUN: lld-link -mingw -dll -out:%t.dll -entry:main %t.obj -implib:%t.lib
+# RUN: llvm-readobj %t.lib | FileCheck %s
+
+# CHECK: Symbol: __imp__func
+# CHECK: Symbol: _func
+
+.global _main
+.global _func
+.text
+_main:
+  ret
+_func:
+  ret
+.section .drectve
+.ascii "-export:func"