[LLD] [COFF, MinGW] Implement the GNU ld options -S/--strip-debug

[mstorsjo]

Summary

In this mode, we retain the symbol table, but skip the actual debug information.

Add an LLD specific option -debug:symtab to lld-link, and hook this up to -S/--strip-debug in the mingw frontend.

Sending in one single review item for simplicity, can commit in two separate commits once it's ok.

[ruiu]

LGTM

lld/trunk/COFF/Config.h

struct Configuration {
   bool DoGC = true;
   bool DoICF = true;
   bool TailMerge;
   bool Relocatable = true;
   bool Force = false;
   bool Debug = false;
   bool DebugDwarf = false;
   bool DebugGHashes = false;
+  bool DebugSymtab = false;
   bool ShowTiming = false;
   unsigned DebugTypes = static_cast<unsigned>(DebugType::None);
   std::vector<std::string> NatvisFiles;
   llvm::SmallString<128> PDBAltPath;
   llvm::SmallString<128> PDBPath;
   std::vector<llvm::StringRef> Argv;
 
   // Symbols in this set are considered as live by the garbage collector.

lld/trunk/COFF/Driver.cpp

Config->Incremental =
                        !Args.hasArg(OPT_profile));
   Config->IntegrityCheck =
       Args.hasFlag(OPT_integritycheck, OPT_integritycheck_no, false);
   Config->NxCompat = Args.hasFlag(OPT_nxcompat, OPT_nxcompat_no, true);
   Config->TerminalServerAware =
       !Config->DLL && Args.hasFlag(OPT_tsaware, OPT_tsaware_no, true);
   Config->DebugDwarf = Args.hasArg(OPT_debug_dwarf);
   Config->DebugGHashes = Args.hasArg(OPT_debug_ghash);
+  Config->DebugSymtab = Args.hasArg(OPT_debug_symtab);
 
   Config->MapFile = getMapFile(Args);
 
   if (Config->Incremental && Args.hasArg(OPT_profile)) {
     warn("ignoring '/incremental' due to '/profile' specification");
     Config->Incremental = false;
   }
 

lld/trunk/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 debug_ghash : F<"debug:ghash">;
 def debug_dwarf : F<"debug:dwarf">;
+def debug_symtab : F<"debug:symtab">;
 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:">;
 def rsp_quoting : Joined<["--"], "rsp-quoting=">,
   HelpText<"Quoting style for response files, 'windows' (default) or 'posix'">;
 def dash_dash_version : Flag<["--"], "version">,

lld/trunk/COFF/Writer.cpp

void Writer::createSymbolAndStringTable() {
   for (OutputSection *Sec : OutputSections) {
     if (Sec->Name.size() <= COFF::NameSize)
       continue;
     if ((Sec->Header.Characteristics & IMAGE_SCN_MEM_DISCARDABLE) == 0)
       continue;
     Sec->setStringTableOff(addEntryToStringTable(Sec->Name));
   }
 
-  if (Config->DebugDwarf) {
+  if (Config->DebugDwarf || Config->DebugSymtab) {
     for (ObjFile *File : ObjFile::Instances) {
       for (Symbol *B : File->getSymbols()) {
         auto *D = dyn_cast_or_null<Defined>(B);
         if (!D || D->WrittenToSymtab)
           continue;
         D->WrittenToSymtab = true;
 
         if (Optional<coff_symbol16> Sym = createSymbol(D))

lld/trunk/test/COFF/sort-debug.test

 # RUN: yaml2obj < %s > %t.obj
 # RUN: lld-link /debug /out:%t.exe /entry:main %t.obj
 # RUN: llvm-readobj -sections %t.exe | FileCheck %s
+# RUN: lld-link /debug:dwarf /out:%t.exe /entry:main %t.obj
+# RUN: llvm-readobj -sections %t.exe | FileCheck %s
+# RUN: lld-link /out:%t.exe /entry:main %t.obj
+# RUN: llvm-readobj -sections %t.exe | FileCheck -check-prefix=NODEBUG %s
+# RUN: lld-link /debug:symtab /out:%t.exe /entry:main %t.obj
+# RUN: llvm-readobj -sections %t.exe | FileCheck -check-prefix=NODEBUG %s
 
 # CHECK: Name: .text
 # CHECK: Name: .debug_abbrev
 # CHECK: Name: .debug_info
 # CHECK: Name: .debug_line
 # CHECK: Name: .debug_pubnames
 # CHECK: Name: .debug_pubtypes
 # CHECK: Name: .reloc
 
+# NODEBUG: Name: .text
+# NODEBUG-NOT: Name: .debug_abbrev
+# NODEBUG-NOT: Name: .debug_info
+# NODEBUG-NOT: Name: .debug_line
+# NODEBUG-NOT: Name: .debug_pubnames
+# NODEBUG-NOT: Name: .debug_pubtypes
+# NODEBUG: Name: .reloc
 
 --- !COFF
 header:
   Machine:         IMAGE_FILE_MACHINE_I386
   Characteristics: [  ]
 sections:
   - Name:            .text
     Characteristics: [ IMAGE_SCN_CNT_CODE, IMAGE_SCN_MEM_EXECUTE, IMAGE_SCN_MEM_READ ]

lld/trunk/test/COFF/symtab.test

 # RUN: yaml2obj < %s > %t.obj
 # RUN: lld-link /debug:dwarf /out:%t.exe /entry:main %t.obj %p/Inputs/std64.lib
 # RUN: llvm-readobj -symbols %t.exe | FileCheck %s
 # RUN: lld-link /debug:dwarf /opt:noref /out:%t.exe /entry:main %t.obj %p/Inputs/std64.lib
 # RUN: llvm-readobj -symbols %t.exe | FileCheck %s
+# RUN: lld-link /debug:symtab /opt:noref /out:%t.exe /entry:main %t.obj %p/Inputs/std64.lib
+# RUN: llvm-readobj -symbols %t.exe | FileCheck %s
 
 # RUN: lld-link /debug /out:%t.exe /entry:main %t.obj %p/Inputs/std64.lib
 # RUN: llvm-readobj -symbols %t.exe | FileCheck -check-prefix=NO %s
 
 # CHECK:      Symbols [
 # CHECK-NEXT:   Symbol {
 # CHECK-NEXT:     Name: .text
 # CHECK-NEXT:     Value: 0