[LLD] [MinGW] Implement the --exclude-symbols option

This adds support for the existing GNU ld command line option, which
allows excluding individual symbols from autoexport (when linking a
DLL and no symbols are marked explicitly as dllexported).

Differential Revision: https://reviews.llvm.org/D130118

Author: mstorsjo

lld/COFF/Driver.cpp

@@ -1315,6 +1315,13 @@ void LinkerDriver::maybeExportMinGWSymbols(const opt::InputArgList &args) {
     if (Optional<StringRef> path = doFindFile(arg->getValue()))
       exporter.addWholeArchive(*path);
 
+  for (auto *arg : args.filtered(OPT_exclude_symbols)) {
+    SmallVector<StringRef, 2> vec;
+    StringRef(arg->getValue()).split(vec, ',');
+    for (StringRef sym : vec)
+      exporter.addExcludedSymbol(mangle(sym));
+  }
+
   ctx.symtab.forEachSymbol([&](Symbol *s) {
     auto *def = dyn_cast<Defined>(s);
     if (!exporter.shouldExport(ctx, def))

lld/COFF/MinGW.cpp

@@ -122,6 +122,10 @@ void AutoExporter::addWholeArchive(StringRef path) {
   excludeLibs.erase(libName);
 }
 
+void AutoExporter::addExcludedSymbol(StringRef symbol) {
+  excludeSymbols.insert(symbol);
+}
+
 bool AutoExporter::shouldExport(const COFFLinkerContext &ctx,
                                 Defined *sym) const {
   if (!sym || !sym->getChunk())

lld/COFF/MinGW.h

@@ -27,6 +27,7 @@ class AutoExporter {
   AutoExporter();
 
   void addWholeArchive(StringRef path);
+  void addExcludedSymbol(StringRef symbol);
 
   llvm::StringSet<> excludeSymbols;
   llvm::StringSet<> excludeSymbolPrefixes;

lld/COFF/Options.td

@@ -45,6 +45,8 @@ def diasdkdir : P<"diasdkdir", "Set the location of the DIA SDK">;
 def entry   : P<"entry", "Name of entry point symbol">;
 def errorlimit : P<"errorlimit",
     "Maximum number of errors to emit before stopping (0 = no limit)">;
+def exclude_symbols  : P<"exclude-symbols", "Exclude symbols from automatic export">,
+    MetaVarName<"<symbol[,symbol,...]>">;
 def export  : P<"export", "Export a function">;
 // No help text because /failifmismatch is not intended to be used by the user.
 def failifmismatch : P<"failifmismatch", "">;

lld/MinGW/Driver.cpp

@@ -398,6 +398,8 @@ bool mingw::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
     add("-delayload:" + StringRef(a->getValue()));
   for (auto *a : args.filtered(OPT_wrap))
     add("-wrap:" + StringRef(a->getValue()));
+  for (auto *a : args.filtered(OPT_exclude_symbols))
+    add("-exclude-symbols:" + StringRef(a->getValue()));
 
   std::vector<StringRef> searchPaths;
   for (auto *a : args.filtered(OPT_L)) {

lld/MinGW/Options.td

@@ -62,6 +62,8 @@ def enable_stdcall_fixup: F<"enable-stdcall-fixup">,
 defm entry: Eq<"entry", "Name of entry point symbol">, MetaVarName<"<entry>">;
 def exclude_all_symbols: F<"exclude-all-symbols">,
     HelpText<"Don't automatically export any symbols">;
+defm exclude_symbols: Eq<"exclude-symbols",
+    "Exclude symbols from automatic export">, MetaVarName<"<symbol[,symbol,...]>">;
 def export_all_symbols: F<"export-all-symbols">,
     HelpText<"Export all symbols even if a def file or dllexport attributes are used">;
 defm fatal_warnings: B<"fatal-warnings",

lld/docs/ReleaseNotes.rst

@@ -39,7 +39,8 @@ COFF Improvements
 MinGW Improvements
 ------------------
 
-* ...
+* The ``--exclude-symbols`` option is now supported.
+  (`D130118 <https://reviews.llvm.org/D130118>`_)
 
 MachO Improvements
 ------------------

lld/test/COFF/exclude-symbols.s

@@ -0,0 +1,20 @@
+// REQUIRES: x86
+// RUN: llvm-mc -filetype=obj -triple=i686-win32-gnu %s -o %t.o
+
+// RUN: lld-link -lldmingw -dll -out:%t.dll %t.o -noentry -exclude-symbols:sym2,unknownsym -exclude-symbols:unknownsym,sym3
+// RUN: llvm-readobj --coff-exports %t.dll | FileCheck --implicit-check-not=Name: %s
+
+// CHECK: Name:
+// CHECK: Name: sym1
+
+.global _sym1
+_sym1:
+  ret
+
+.global _sym2
+_sym2:
+  ret
+
+.global _sym3
+_sym3:
+  ret

lld/test/MinGW/driver.test

@@ -321,6 +321,10 @@ RUN: ld.lld -### -m i386pep foo.o -wrap foo1 --wrap foo2 2>&1 | FileCheck -check
 RUN: ld.lld -### -m i386pep foo.o -wrap=foo1 --wrap=foo2 2>&1 | FileCheck -check-prefix WRAP %s
 WRAP: -wrap:foo1 -wrap:foo2
 
+RUN: ld.lld -### -m i386pep foo.o -exclude-symbols sym1,sym2 --exclude-symbols sym3 2>&1 | FileCheck -check-prefix EXCLUDE_SYMBOLS %s
+RUN: ld.lld -### -m i386pep foo.o -exclude-symbols=sym1,sym2 --exclude-symbols=sym3 2>&1 | FileCheck -check-prefix EXCLUDE_SYMBOLS %s
+EXCLUDE_SYMBOLS: -exclude-symbols:sym1,sym2 -exclude-symbols:sym3
+
 RUN: ld.lld -### -m i386pep foo.o 2>&1 | FileCheck -check-prefix DEMANGLE %s
 RUN: ld.lld -### -m i386pep foo.o -demangle 2>&1 | FileCheck -check-prefix DEMANGLE %s
 RUN: ld.lld -### -m i386pep foo.o --demangle 2>&1 | FileCheck -check-prefix DEMANGLE %s