[COFF] Add support for the GNU ld flag --kill-at

GNU ld has got a number of different flags for adjusting how to
behave around stdcall functions. The --kill-at flag strips the
trailing sdcall suffix from exported functions (which otherwise
is included by default in MinGW setups).

This also strips it from the corresponding import library though.
That makes it hard to link to such an import library from code
that calls the functions - but this matches what GNU ld does with
this flag. Therefore, this flag is probably not sensibly used
together with import libraries, but probably mostly when creating
some sort of plugin, or if creating the import library separately
with dlltool.

Differential Revision: https://reviews.llvm.org/D44292

llvm-svn: 327561

lld/COFF/Config.h

@@ -190,6 +190,7 @@ struct Configuration {
   bool WarnMissingOrderSymbol = true;
   bool WarnLocallyDefinedImported = true;
   bool Incremental = true;
+  bool KillAt = false;
 };
 
 extern Configuration *Config;

lld/COFF/Driver.cpp

@@ -1073,6 +1073,10 @@ void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   if (Args.hasArg(OPT_lldsavetemps))
     Config->SaveTemps = true;
 
+  // Handle /kill-at
+  if (Args.hasArg(OPT_kill_at))
+    Config->KillAt = true;
+
   // Handle /lldltocache
   if (auto *Arg = Args.getLastArg(OPT_lldltocache))
     Config->LTOCache = Arg->getValue();

lld/COFF/DriverUtils.cpp

@@ -582,6 +582,26 @@ static StringRef undecorate(StringRef Sym) {
   return Sym.startswith("_") ? Sym.substr(1) : Sym;
 }
 
+// Convert stdcall/fastcall style symbols into unsuffixed symbols,
+// with or without a leading underscore. (MinGW specific.)
+static StringRef killAt(StringRef Sym, bool Prefix) {
+  if (Sym.empty())
+    return Sym;
+  // Strip any trailing stdcall suffix
+  Sym = Sym.substr(0, Sym.find('@', 1));
+  if (!Sym.startswith("@")) {
+    if (Prefix && !Sym.startswith("_"))
+      return Saver.save("_" + Sym);
+    return Sym;
+  }
+  // For fastcall, remove the leading @ and replace it with an
+  // underscore, if prefixes are used.
+  Sym = Sym.substr(1);
+  if (Prefix)
+    Sym = Saver.save("_" + Sym);
+  return Sym;
+}
+
 // Performs error checking on all /export arguments.
 // It also sets ordinals.
 void fixupExports() {
@@ -614,6 +634,15 @@ void fixupExports() {
     }
   }
 
+  if (Config->KillAt && Config->Machine == I386) {
+    for (Export &E : Config->Exports) {
+      E.Name = killAt(E.Name, true);
+      E.ExportName = killAt(E.ExportName, false);
+      E.ExtName = killAt(E.ExtName, true);
+      E.SymbolName = killAt(E.SymbolName, true);
+    }
+  }
+
   // Uniquefy by name.
   DenseMap<StringRef, Export *> Map(Config->Exports.size());
   std::vector<Export> V;

lld/COFF/Options.td

@@ -126,6 +126,7 @@ def help_q : Flag<["/?", "-?"], "">, Alias<help>;
 def debug_ghash : F<"debug:ghash">;
 def debug_dwarf : F<"debug:dwarf">;
 def export_all_symbols : F<"export-all-symbols">;
+def kill_at : F<"kill-at">;
 def lldmingw : F<"lldmingw">;
 def msvclto : F<"msvclto">;
 def output_def : Joined<["/", "-"], "output-def:">;

lld/test/COFF/def-export-stdcall.s

@@ -44,7 +44,8 @@
 # DECORATED-EXPORTS: Name: vectorcall@@8
 
 
-# RUN: echo -e "LIBRARY foo\nEXPORTS\n  stdcall@8\n  @fastcall@8" > %t.def
+# GNU tools don't support vectorcall at the moment, but test it for completeness.
+# RUN: echo -e "LIBRARY foo\nEXPORTS\n  stdcall@8\n  @fastcall@8\n  vectorcall@@8" > %t.def
 # RUN: lld-link -lldmingw -entry:dllmain -dll -def:%t.def %t.obj -out:%t.dll -implib:%t.lib
 # RUN: llvm-readobj %t.lib | FileCheck -check-prefix DECORATED-MINGW-IMPLIB %s
 # RUN: llvm-readobj -coff-exports %t.dll | FileCheck -check-prefix DECORATED-MINGW-EXPORTS %s
@@ -55,9 +56,39 @@
 # DECORATED-MINGW-IMPLIB: Name type: noprefix
 # DECORATED-MINGW-IMPLIB-NEXT: __imp__stdcall@8
 # DECORATED-MINGW-IMPLIB-NEXT: _stdcall@8
+# GNU tools don't support vectorcall, but this test is just to track that
+# lld's behaviour remains consistent over time.
+# DECORATED-MINGW-IMPLIB: Name type: name
+# DECORATED-MINGW-IMPLIB-NEXT: __imp_vectorcall@@8
+# DECORATED-MINGW-IMPLIB-NEXT: vectorcall@@8
 
 # DECORATED-MINGW-EXPORTS: Name: @fastcall@8
 # DECORATED-MINGW-EXPORTS: Name: stdcall@8
+# DECORATED-MINGW-EXPORTS: Name: vectorcall@@8
+
+# RUN: lld-link -lldmingw -kill-at -entry:dllmain -dll -def:%t.deco-mingw.def %t.obj -out:%t.dll -implib:%t.lib
+# RUN: llvm-readobj %t.lib | FileCheck -check-prefix MINGW-KILL-AT-IMPLIB %s
+# RUN: llvm-readobj -coff-exports %t.dll | FileCheck -check-prefix MINGW-KILL-AT-EXPORTS %s
+
+# RUN: lld-link -lldmingw -kill-at -entry:dllmain -dll %t.obj -out:%t.dll -implib:%t.lib
+# RUN: llvm-readobj %t.lib | FileCheck -check-prefix MINGW-KILL-AT-IMPLIB %s
+# RUN: llvm-readobj -coff-exports %t.dll | FileCheck -check-prefix MINGW-KILL-AT-EXPORTS %s
+
+# MINGW-KILL-AT-IMPLIB: Name type: noprefix
+# MINGW-KILL-AT-IMPLIB: __imp__fastcall
+# MINGW-KILL-AT-IMPLIB-NEXT: _fastcall
+# MINGW-KILL-AT-IMPLIB: Name type: noprefix
+# MINGW-KILL-AT-IMPLIB-NEXT: __imp__stdcall
+# MINGW-KILL-AT-IMPLIB-NEXT: _stdcall
+# GNU tools don't support vectorcall, but this test is just to track that
+# lld's behaviour remains consistent over time.
+# MINGW-KILL-AT-IMPLIB: Name type: noprefix
+# MINGW-KILL-AT-IMPLIB-NEXT: __imp__vectorcall
+# MINGW-KILL-AT-IMPLIB-NEXT: _vectorcall
+
+# MINGW-KILL-AT-EXPORTS: Name: fastcall
+# MINGW-KILL-AT-EXPORTS: Name: stdcall
+# MINGW-KILL-AT-EXPORTS: Name: vectorcall
 
 
         .def     _stdcall@8;