[ELF] Implement --strip-all/-s

[davide]

Summary

--strip-debug will follow. Let me know if adding another private member of ElfLinkingContext or you want stripSymbols to grow up to something that can accomodate more than 2 values, e.g. an enum. I haven't strong preferences.

[• shankar.easwaran]

Lgtm

include/lld/ReaderWriter/ELFLinkingContext.h

public:
   std::string demangle(StringRef symbolName) const override;
   bool demangleSymbols() const { return _demangle; }
   void setDemangleSymbols(bool d) { _demangle = d; }
 
   /// \brief Align segments.
   bool alignSegments() const { return _alignSegments; }
   void setAlignSegments(bool align) { _alignSegments = align; }
 
+  /// \brief Strip symbols.
+  bool stripSymbols() const { return _stripSymbols; }
+  void setStripSymbols(bool strip) { _stripSymbols = strip; }
+
   // We can parse several linker scripts via command line whose ASTs are stored
   // in the current linking context via addLinkerScript().
   void addLinkerScript(std::unique_ptr<script::Parser> script) {
     _scripts.push_back(std::move(script));
   }
 
 private:
   ELFLinkingContext() LLVM_DELETED_FUNCTION;
protected:
   bool _noInhibitExec;
   bool _exportDynamic;
   bool _mergeCommonStrings;
   bool _useShlibUndefines;
   bool _dynamicLinkerArg;
   bool _noAllowDynamicLibraries;
   bool _mergeRODataToTextSegment;
   bool _demangle;
+  bool _stripSymbols;
   bool _alignSegments;
   bool _nostdlib;
   llvm::Optional<uint64_t> _maxPageSize;
 
   OutputMagic _outputMagic;
   StringRefVector _inputSearchPaths;
   std::unique_ptr<Writer> _writer;
   StringRef _dynamicLinkerPath;

lib/Driver/GnuLdDriver.cpp

for (auto inputArg : *parsedArgs) {
     case OPT_rpath_link: {
       SmallVector<StringRef, 2> rpaths;
       StringRef(inputArg->getValue()).split(rpaths, ":");
       for (auto path : rpaths)
         ctx->addRpathLink(path);
       break;
     }
 
+    case OPT_strip_all: {
+      ctx->setStripSymbols(true);
+      break;
+    }
+
     case OPT_soname:
       ctx->setSharedObjectName(inputArg->getValue());
       break;
 
     case OPT_rosegment:
       ctx->setCreateSeparateROSegment();
       break;
 

lib/Driver/GnuLdOptions.td

 def grp_symbolopts : OptionGroup<"opts">,
      HelpText<"SYMBOL OPTIONS">;
 def demangle : Flag<["--"], "demangle">,
      HelpText<"Demangle C++ symbols">,
      Group<grp_symbolopts>;
 def no_demangle : Flag<["--"], "no-demangle">,
      HelpText<"Dont demangle C++ symbols">,
      Group<grp_symbolopts>;
+def strip_all : Flag<["--"], "strip-all">,
+     HelpText<"Omit all symbol informations from output">,
+     Group<grp_symbolopts>;
+def alias_strip_all : Flag<["-"], "s">,
+     Alias<strip_all>;
 
 //===----------------------------------------------------------------------===//
 /// Optimization Options
 //===----------------------------------------------------------------------===//
 def grp_opts : OptionGroup<"opts">,
      HelpText<"OPTIMIZATIONS">;
 def hash_style : Joined <["--"], "hash-style=">,
      HelpText<"Set the type of linker's hash table(s)">,

lib/ReaderWriter/ELF/ELFLinkingContext.cpp

 
 ELFLinkingContext::ELFLinkingContext(
     llvm::Triple triple, std::unique_ptr<TargetHandlerBase> targetHandler)
     : _outputELFType(llvm::ELF::ET_EXEC), _triple(triple),
       _targetHandler(std::move(targetHandler)), _baseAddress(0),
       _isStaticExecutable(false), _noInhibitExec(false), _exportDynamic(false),
       _mergeCommonStrings(false), _useShlibUndefines(true),
       _dynamicLinkerArg(false), _noAllowDynamicLibraries(false),
-      _mergeRODataToTextSegment(true), _demangle(true), _alignSegments(true),
+      _mergeRODataToTextSegment(true), _demangle(true),
+      _stripSymbols(false), _alignSegments(true),
       _outputMagic(OutputMagic::DEFAULT), _initFunction("_init"),
       _finiFunction("_fini"), _sysrootPath("") {}
 
 void ELFLinkingContext::addPasses(PassManager &pm) {
   pm.add(llvm::make_unique<elf::OrderPass>());
 }
 
 uint16_t ELFLinkingContext::getOutputMachine() const {

lib/ReaderWriter/ELF/OutputELFWriter.h

std::error_code OutputELFWriter<ELFT>::buildOutput(const File &file) {
 
   // Finalize the default value of symbols that the linker adds
   finalizeDefaultAtomValues();
 
   // Build the Atom To Address map for applying relocations
   buildAtomToAddressMap(file);
 
   // Create symbol table and section string table
+  // Do it only if -s is not specified.
+  if (!_context.stripSymbols())
     buildStaticSymbolTable(file);
 
   // Finalize the layout by calling the finalize() functions
   _layout.finalize();
 
   // build Section Header table
   buildSectionHeaderTable();
 
   // assign Offsets and virtual addresses

test/elf/strip-all.test

+# Tests the --strip-all (-s) flag. We expect the symbol table to not contain
+# any symbol in the output file.
+#
+# The following code was used to generate the object.
+# $ clang -c blah.c -o blah
+#
+# void
+# callMeMaybe(int *v)
+# {
+# *v += 1;
+# }
+#
+# int
+# main(void)
+# {
+#
+# int blah = 42;
+# callMeMaybe(&blah);
+# }
+
+#RUN: yaml2obj -format=elf %s -o=%t.o
+#RUN: lld -flavor gnu -target x86_64 %t.o -e=main --strip-all -o %t1
+#RUN: llvm-readobj -dt %t1 | FileCheck -check-prefix CHECKSYMS %s
+
+#CHECKSYMS: @
+
+---
+FileHeader:      
+  Class:           ELFCLASS64
+  Data:            ELFDATA2LSB
+  OSABI:           ELFOSABI_FREEBSD
+  Type:            ET_REL
+  Machine:         EM_X86_64
+Sections:        
+  - Name:            .text
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC, SHF_EXECINSTR ]
+    AddressAlign:    0x0000000000000010
+    Content:         554889E548897DF8488B7DF88B07050100000089075DC3660F1F840000000000554889E54883EC10488D7DFCC745FC2A000000E8C8FFFFFFB8000000004883C4105DC3
+  - Name:            .data
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x0000000000000004
+    Content:         ''
+  - Name:            .bss
+    Type:            SHT_NOBITS
+    Flags:           [ SHF_WRITE, SHF_ALLOC ]
+    AddressAlign:    0x0000000000000004
+    Content:         ''
+  - Name:            .comment
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_MERGE, SHF_STRINGS ]
+    AddressAlign:    0x0000000000000001
+    Content:         004672656542534420636C616E672076657273696F6E20332E342E312028746167732F52454C454153455F33342F646F74312D66696E616C203230383033322920323031343035313200
+  - Name:            .note.GNU-stack
+    Type:            SHT_PROGBITS
+    AddressAlign:    0x0000000000000001
+    Content:         ''
+  - Name:            .eh_frame
+    Type:            SHT_PROGBITS
+    Flags:           [ SHF_ALLOC ]
+    AddressAlign:    0x0000000000000008
+    Content:         1400000000000000017A5200017810011B0C070890010000180000001C000000000000001700000000410E108602430D060000001800000038000000000000002300000000410E108602430D06000000
+  - Name:            .rela.eh_frame
+    Type:            SHT_RELA
+    Link:            .symtab
+    AddressAlign:    0x0000000000000008
+    Info:            .eh_frame
+    Relocations:     
+      - Offset:          0x0000000000000020
+        Symbol:          .text
+        Type:            R_X86_64_PC32
+      - Offset:          0x000000000000003C
+        Symbol:          .text
+        Type:            R_X86_64_PC32
+        Addend:          32
+Symbols:         
+  Local:           
+    - Name:            .text
+      Type:            STT_SECTION
+      Section:         .text
+    - Name:            .data
+      Type:            STT_SECTION
+      Section:         .data
+    - Name:            .bss
+      Type:            STT_SECTION
+      Section:         .bss
+    - Name:            .comment
+      Type:            STT_SECTION
+      Section:         .comment
+    - Name:            .note.GNU-stack
+      Type:            STT_SECTION
+      Section:         .note.GNU-stack
+    - Name:            .eh_frame
+      Type:            STT_SECTION
+      Section:         .eh_frame
+  Global:          
+    - Name:            callMeMaybe
+      Type:            STT_FUNC
+      Section:         .text
+      Size:            0x0000000000000017
+    - Name:            main
+      Type:            STT_FUNC
+      Section:         .text
+      Value:           0x0000000000000020
+      Size:            0x0000000000000023
+...