[ELF2] --strip-all/-s command line implemented

[grimar]

Summary

-s, --strip-all - Strip all symbols
Implementation removes .strtab and .symtab sections from output.

Test from lld\test\elf branch was taken as a base, but was improved in part of checks.

[ruiu]

ELF/Writer.cpp

118–119

This is a bit confusing. Let's do this

std::unique_ptr<SymbolTableSection<ELFT>> SymTab;
if (!Config->StripAll) {
  SymTab.reset(new SymbolTableSection<ELFT>(*Symtab, *Out<ELFT>::StrTab);
  Out<ELFT>::SymTab = SymTab.get();
}

[grimar]

ELF/Writer.cpp

118–119

I thought about something like that, just didn`t know will it keep code consistency or not. I agree, that will be better.

btw, the same can be applied for RelaPlt and GotPlt since we dont need to create them when lazy relocs are off. (not for this patch)

[davide]

Structure looks good, just few comments.

ELF/Config.h

60–62

This is not sorted.

ELF/Options.td

92

Can't you just say "strip all symbols" as gold and ld do?

test/elf2/strip-all.s

2

Please do not use obj2yaml, but use assembler for tests. This is the standard for the new ELF linker.

[grimar]

ELF/Config.h

60–62

Will fix.
I forgot that after first two characters there are still other ones, sorry :)

ELF/Options.td

92

I took it from man ld, but will replace if you wish.

test/elf2/strip-all.s

2

Ok. I expected that. Thats explains why I never saw its usings in new ELF branch.

[davide]

ELF/Options.td

92

This is what I see on FreeBSD. I would not deviate from that as it's shorter and captures the essence anyway (which I think is better for --help output)
davide@ganondorf:~ % /usr/local/bin/ld.bfd --help | grep strip-all

-s, --strip-all             Strip all symbols

davide@ganondorf:~ % /usr/local/bin/ld.gold --help | grep strip-all

-s, --strip-all             Strip all symbols

Thanks,

Davide

[grimar]

Review comments addressed.

[ruiu]

LGTM

ELF/Config.h

struct Configuration {
   bool EnableNewDtags;
   bool ExportDynamic;
   bool GcSections;
   bool GnuHash = false;
   bool Mips64EL = false;
   bool NoInhibitExec;
   bool NoUndefined;
   bool Shared;
   bool Static = false;
+  bool StripAll;
   bool SysvHash = true;
   bool Verbose;
   bool ZNodelete = false;
   bool ZNow = false;
   bool ZOrigin = false;
   ELFKind EKind = ELFNoneKind;
   uint16_t EMachine = llvm::ELF::EM_NONE;
   uint64_t EntryAddr = -1;
 };
 
 extern Configuration *Config;
 
 } // namespace elf2
 } // namespace lld
 
 #endif

ELF/Driver.cpp

void LinkerDriver::createFiles(opt::InputArgList &Args) {
   Config->DiscardLocals = Args.hasArg(OPT_discard_locals);
   Config->DiscardNone = Args.hasArg(OPT_discard_none);
   Config->EnableNewDtags = !Args.hasArg(OPT_disable_new_dtags);
   Config->ExportDynamic = Args.hasArg(OPT_export_dynamic);
   Config->GcSections = Args.hasArg(OPT_gc_sections);
   Config->NoInhibitExec = Args.hasArg(OPT_noinhibit_exec);
   Config->NoUndefined = Args.hasArg(OPT_no_undefined);
   Config->Shared = Args.hasArg(OPT_shared);
+  Config->StripAll = Args.hasArg(OPT_strip_all);
   Config->Verbose = Args.hasArg(OPT_verbose);
 
   Config->DynamicLinker = getString(Args, OPT_dynamic_linker);
   Config->Entry = getString(Args, OPT_entry);
   Config->Fini = getString(Args, OPT_fini, "_fini");
   Config->Init = getString(Args, OPT_init, "_init");
   Config->OutputFile = getString(Args, OPT_o);
   Config->SoName = getString(Args, OPT_soname);

ELF/Options.td

 def script : Separate<["--"], "script">, HelpText<"Read linker script">;
 
 def shared : Flag<["-"], "shared">,
   HelpText<"Build a shared object">;
 
 def soname : Joined<["-"], "soname=">,
   HelpText<"Set DT_SONAME">;
 
+def strip_all : Flag<["--"], "strip-all">,
+  HelpText<"Strip all symbols">;
+
 def sysroot : Joined<["--"], "sysroot=">,
   HelpText<"Set the system root">;
 
 def undefined : Joined<["--"], "undefined=">,
   HelpText<"Force undefined symbol during linking">;
 
 def verbose : Flag<["--"], "verbose">;
 

 def alias_init_init : Joined<["-"], "init=">, Alias<init>;
 def alias_l__library : Joined<["--"], "library=">, Alias<l>;
 def alias_o_output : Joined<["--"], "output=">, Alias<o>;
 def alias_rpath_rpath : Joined<["-"], "rpath=">, Alias<rpath>;
 def alias_shared_Bshareable : Flag<["-"], "Bshareable">, Alias<shared>;
 def alias_soname_h : Separate<["-"], "h">, Alias<soname>;
 def alias_soname_soname : Separate<["-"], "soname">, Alias<soname>;
 def alias_script_T : Separate<["-"], "T">, Alias<script>;
+def alias_strip_all: Flag<["-"], "s">, Alias<strip_all>;
 def alias_undefined_u : Separate<["-"], "u">, Alias<undefined>;
 
 // Options listed below are silently ignored now.
 def O3 : Flag<["-"], "O3">;
 def build_id : Flag<["--"], "build-id">;
 def eh_frame_hdr : Flag<["--"], "eh-frame-hdr">;
 def end_group : Flag<["--"], "end-group">;
 def fatal_warnings : Flag<["--"], "fatal-warnings">;
 def no_add_needed : Flag<["--"], "no-add-needed">;
 def no_fatal_warnings : Flag<["--"], "no-fatal-warnings">;
 def no_warn_mismatch : Flag<["--"], "no-warn-mismatch">;
 def start_group : Flag<["--"], "start-group">;
-def strip_all : Flag<["--"], "strip-all">;
 def version_script : Separate<["--"], "version-script">;
 def warn_common : Flag<["--"], "warn-common">;
 def warn_shared_textrel : Flag<["--"], "warn-shared-textrel">;

ELF/Writer.cpp

 template <class ELFT> void lld::elf2::writeResult(SymbolTable<ELFT> *Symtab) {
   // Initialize output sections that are handled by Writer specially.
   // Don't reorder because the order of initialization matters.
   InterpSection<ELFT> Interp;
   Out<ELFT>::Interp = &Interp;
   StringTableSection<ELFT> ShStrTab(".shstrtab", false);
   Out<ELFT>::ShStrTab = &ShStrTab;
   StringTableSection<ELFT> StrTab(".strtab", false);
+  if (!Config->StripAll)
     Out<ELFT>::StrTab = &StrTab;
   StringTableSection<ELFT> DynStrTab(".dynstr", true);
   Out<ELFT>::DynStrTab = &DynStrTab;
   OutputSection<ELFT> Bss(".bss", SHT_NOBITS, SHF_ALLOC | SHF_WRITE);
   Out<ELFT>::Bss = &Bss;
   GotSection<ELFT> Got;
   Out<ELFT>::Got = &Got;
   GotPltSection<ELFT> GotPlt;
   if (Target->supportsLazyRelocations())
     Out<ELFT>::GotPlt = &GotPlt;
   PltSection<ELFT> Plt;
   Out<ELFT>::Plt = &Plt;
-  SymbolTableSection<ELFT> SymTab(*Symtab, *Out<ELFT>::StrTab);
-  Out<ELFT>::SymTab = &SymTab;
+  std::unique_ptr<SymbolTableSection<ELFT>> SymTab;
+  if (!Config->StripAll) {
+    SymTab.reset(new SymbolTableSection<ELFT>(*Symtab, *Out<ELFT>::StrTab));
+    Out<ELFT>::SymTab = SymTab.get();
+  }
   SymbolTableSection<ELFT> DynSymTab(*Symtab, *Out<ELFT>::DynStrTab);
   Out<ELFT>::DynSymTab = &DynSymTab;
   HashTableSection<ELFT> HashTab;
   if (Config->SysvHash)
     Out<ELFT>::HashTab = &HashTab;
   GnuHashTableSection<ELFT> GnuHashTab;
   if (Config->GnuHash)
     Out<ELFT>::GnuHashTab = &GnuHashTab;
   bool IsRela = Symtab->shouldUseRela();
   RelocationSection<ELFT> RelaDyn(IsRela ? ".rela.dyn" : ".rel.dyn", IsRela);

 template <class ELFT> void Writer<ELFT>::copyLocalSymbols() {
   for (const std::unique_ptr<ObjectFile<ELFT>> &F : Symtab.getObjectFiles()) {
     for (const Elf_Sym &Sym : F->getLocalSymbols()) {
       ErrorOr<StringRef> SymNameOrErr = Sym.getName(F->getStringTable());
       error(SymNameOrErr);
       StringRef SymName = *SymNameOrErr;
       if (!shouldKeepInSymtab<ELFT>(*F, SymName, Sym))
         continue;
+      if (Out<ELFT>::SymTab)
         Out<ELFT>::SymTab->addLocalSymbol(SymName);
     }
   }
 }
 
 // PPC64 has a number of special SHT_PROGBITS+SHF_ALLOC+SHF_WRITE sections that
 // we would like to make sure appear is a specific order to maximize their
 // coverage by a single signed 16-bit offset from the TOC base pointer.
 // Conversely, the special .tocbss section should be first among all SHT_NOBITS
for (auto &P : Symtab.getSymbols()) {
     if (auto *U = dyn_cast<Undefined<ELFT>>(Body))
       if (!U->isWeak() && !U->canKeepUndefined())
         reportUndefined<ELFT>(Symtab, *Body);
 
     if (auto *C = dyn_cast<DefinedCommon<ELFT>>(Body))
       CommonSymbols.push_back(C);
     if (!includeInSymtab<ELFT>(*Body))
       continue;
+    if (Out<ELFT>::SymTab)
       Out<ELFT>::SymTab->addSymbol(Body);
 
     if (isOutputDynamic() && includeInDynamicSymtab(*Body))
       Out<ELFT>::DynSymTab->addSymbol(Body);
   }
   addCommonSymbols(CommonSymbols);
 
   // This order is not the same as the final output order
   // because we sort the sections using their attributes below.
+  if (Out<ELFT>::SymTab)
     OutputSections.push_back(Out<ELFT>::SymTab);
   OutputSections.push_back(Out<ELFT>::ShStrTab);
+  if (Out<ELFT>::StrTab)
     OutputSections.push_back(Out<ELFT>::StrTab);
   if (isOutputDynamic()) {
     OutputSections.push_back(Out<ELFT>::DynSymTab);
     if (Out<ELFT>::GnuHashTab)
       OutputSections.push_back(Out<ELFT>::GnuHashTab);
     if (Out<ELFT>::HashTab)
       OutputSections.push_back(Out<ELFT>::HashTab);
     OutputSections.push_back(Out<ELFT>::Dynamic);
     OutputSections.push_back(Out<ELFT>::DynStrTab);

test/elf2/strip-all.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: ld.lld2 %t -o %t1
+#RUN: llvm-objdump -section-headers %t1 | FileCheck %s -check-prefix BEFORE
+#BEFORE:       4 .symtab 00000030
+#BEFORE-NEXT:  5 .shstrtab 0000002c
+#BEFORE-NEXT:  6 .strtab 00000008
+
+#RUN: ld.lld2 %t.o -e main --strip-all -o %t1
+#RUN: llvm-objdump -section-headers %t1 | FileCheck %s -check-prefix AFTER
+#AFTER-NOT: .symtab
+#AFTER: 7 .shstrtab 0000003f
+#AFTER-NOT: .strtab
+
+# Test alias -s
+#RUN: ld.lld2 %t.o -e main -s -o %t1
+#RUN: llvm-objdump -section-headers %t1 | FileCheck %s -check-prefix AFTER
+
+# exits with return code 42 on linux
+.globl _start;
+_start:
+  mov $60, %rax
+  mov $42, %rdi
+  syscall