[1/3] [LLD] [MinGW] Implement the --exclude-symbols option

[mstorsjo]

Summary

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).

I haven't seen this option used in the wild anywhere, but I'm
implementing it as a stepping stone for something more useful.

[mati865]

LGTM with minor question.

lld/COFF/Options.td

48

I don't have experience with MSVC tools so cannot tell but will this message be clear enough for people used to MSVC that they have to pass comma separated symbol names?

[mstorsjo]

lld/COFF/Options.td

48

I guess I could add an MetaVarName to make it clearer, like in the mingw options file.

[mstorsjo]

Added a MetaVarName in COFF/Options.td.

[mstorsjo]

Ping, @mati865 @rnk - does either of you want to give the formal approval here?

[mati865]

Sorry, haven't noticed the approval was reset.

EDIT: ah, I probably haven't checked the box back then.

[rnk]

lgtm

[MaskRay]

lld/test/COFF/exclude-symbols.s

6

grep Name: can be expressed with pure FileCheck directives with --implicit-check-not=Name:

// CHECK: Name:
// CHECK: Name: sym1

[mstorsjo]

lld/test/COFF/exclude-symbols.s

6

Thanks - that seems to work.

[mstorsjo]

Use --implicit-check-not to simplify the testcase a little.

lld/COFF/Driver.cpp

void LinkerDriver::maybeExportMinGWSymbols(const opt::InputArgList &args) {
   }
 
   AutoExporter exporter;
 
   for (auto *arg : args.filtered(OPT_wholearchive_file))
     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))
       return;
 
     if (!def->isGCRoot) {
       def->isGCRoot = true;
       config->gcroot.push_back(def);

lld/COFF/MinGW.h

 
 // Logic for deciding what symbols to export, when exporting all
 // symbols for MinGW.
 class AutoExporter {
 public:
   AutoExporter();
 
   void addWholeArchive(StringRef path);
+  void addExcludedSymbol(StringRef symbol);
 
   llvm::StringSet<> excludeSymbols;
   llvm::StringSet<> excludeSymbolPrefixes;
   llvm::StringSet<> excludeSymbolSuffixes;
   llvm::StringSet<> excludeLibs;
   llvm::StringSet<> excludeObjects;
 
   bool shouldExport(const COFFLinkerContext &ctx, Defined *sym) const;

lld/COFF/MinGW.cpp

 
 void AutoExporter::addWholeArchive(StringRef path) {
   StringRef libName = sys::path::filename(path);
   // Drop the file extension, to match the processing below.
   libName = libName.substr(0, libName.rfind('.'));
   excludeLibs.erase(libName);
 }
 
+void AutoExporter::addExcludedSymbol(StringRef symbol) {
+  excludeSymbols.insert(symbol);
+}
+
 bool AutoExporter::shouldExport(const COFFLinkerContext &ctx,
                                 Defined *sym) const {
   if (!sym || !sym->getChunk())
     return false;
 
   // Only allow the symbol kinds that make sense to export; in particular,
   // disallow import symbols.
   if (!isa<DefinedRegular>(sym) && !isa<DefinedCommon>(sym))

lld/COFF/Options.td

def color_diagnostics_eq: Joined<["--"], "color-diagnostics=">,
     HelpText<"Use colors in diagnostics (default: auto)">,
     MetaVarName<"[auto,always,never]">;
 def defaultlib : P<"defaultlib", "Add the library to the list of input files">;
 def delayload : P<"delayload", "Delay loaded DLL name">;
 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", "">;
 def filealign : P<"filealign", "Section alignment in the output file">;
 def functionpadmin : F<"functionpadmin">;
 def functionpadmin_opt : P<"functionpadmin",
     "Prepares an image for hotpatching">;
 def guard   : P<"guard", "Control flow guard">;

lld/MinGW/Driver.cpp

bool mingw::link(ArrayRef<const char *> argsArr, llvm::raw_ostream &stdoutOS,
   for (auto *a : args.filtered(OPT_require_defined))
     add("-include:" + StringRef(a->getValue()));
   for (auto *a : args.filtered(OPT_undefined))
     add("-includeoptional:" + StringRef(a->getValue()));
   for (auto *a : args.filtered(OPT_delayload))
     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)) {
     searchPaths.push_back(a->getValue());
     add("-libpath:" + StringRef(a->getValue()));
   }
 
   StringRef prefix = "";

lld/MinGW/Options.td

def enable_auto_import: F<"enable-auto-import">,
     HelpText<"Automatically import data symbols from other DLLs where needed">;
 def enable_runtime_pseudo_reloc: F<"enable-runtime-pseudo-reloc">,
     HelpText<"Allow automatic imports that require runtime fixups">;
 def enable_stdcall_fixup: F<"enable-stdcall-fixup">,
     HelpText<"Resolve stdcall/fastcall/vectorcall to undecorated symbols without warnings">;
 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",
     "Treat warnings as errors",
     "Do not treat warnings as errors (default)">;
 defm file_alignment: Eq<"file-alignment", "Set file alignment">;
 defm gc_sections: B<"gc-sections",
     "Remove unused sections",

lld/docs/ReleaseNotes.rst

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

lld/test/COFF/exclude-symbols.s

+// 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

 RUN: ld.lld -### -m i386pep foo.o --allow-multiple-definition --no-allow-multiple-definition 2>&1 | FileCheck -check-prefix NO_ALLOW_MULTIPLE_DEFINITION %s
 RUN: ld.lld -### -m i386pep foo.o -allow-multiple-definition -no-allow-multiple-definition 2>&1 | FileCheck -check-prefix NO_ALLOW_MULTIPLE_DEFINITION %s
 NO_ALLOW_MULTIPLE_DEFINITION-NOT: -force:multiple
 
 RUN: ld.lld -### -m i386pep foo.o -wrap foo1 --wrap foo2 2>&1 | FileCheck -check-prefix WRAP %s
 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
 DEMANGLE: -demangle{{ }}
 
 RUN: ld.lld -### -m i386pep foo.o -no-demangle 2>&1 | FileCheck -check-prefix NO-DEMANGLE %s
 RUN: ld.lld -### -m i386pep foo.o --no-demangle 2>&1 | FileCheck -check-prefix NO-DEMANGLE %s
 NO-DEMANGLE: -demangle:no