[ELF2] -z now option implemented

[grimar]

Summary

When generating an executable or shared library, mark it to tell the dynamic linker to resolve all symbols when the program is started, or when the shared library is linked to using dlopen, instead of deferring function call resolution to the point when the function is first called.

[emaste]

ELF/Options.td

76

Should this be JoinedOrSeparate?

While trying the FreeBSD base system build with LLD I see that -znodelete is passed to the linker.

[grimar]

ELF/Options.td

76

Looks like ld/gold accepts both variants. -help indicates to separate syntax thought.

[ruiu]

ELF/Config.h

37

Name this ZNow so that -z foo would get different name than -foo.

ELF/Driver.cpp

142–144

If doesn't have {} and else has? Please make this consistent.

143

Let's not warn on unknown options for now. They were silently ignored before this patch.

ELF/OutputSections.cpp

319–324

if (Config->Now)
  WriteVal(DT_FLAGS_1, DF_1_NOW);

[grimar]

ELF/Driver.cpp

143

Yes, I know they were. But this is equals to ld behavior now. It shows warnings on unknown -z options. But if you wish I will remove.

ELF/OutputSections.cpp

319–324

There are many possible -z options. And Flag is requred to combine them when at least one more will be added.

[ruiu]

ELF/Driver.cpp

143

Ultimately we will want to warn on unknown options, but for now we ignore lots of options for ease of development, and I think -z is not an exception.

ELF/OutputSections.cpp

319–324

I'd want you to update the code to use a variable when you need the variable. Currently it can be written without that.

[grimar]

All review comments addressed.

ELF/Options.td

76

Changed to JoinedOrSeparate.

[grimar]

ELF/Driver.cpp

142–144

Fixed.

143

Ok.

ELF/OutputSections.cpp

319–324

Ok.

[ruiu]

LGTM with a nit.

ELF/Driver.cpp

138–142

This can be

for (auto *Arg : Args.filtered(OPT_z))
  if (Arg->getValue() == "now")
    Config->ZNow = true;

[grimar]

ELF/Driver.cpp

138–142

Unfortunately no because getValue() returns char*.

I'll rewrite to:

if (Arg->getValue() == StringRef("now"))
  Config->ZNow = true;

ELF/Config.h

struct Configuration {
   std::vector<llvm::StringRef> InputSearchPaths;
   bool AllowMultipleDefinition;
   bool DiscardAll;
   bool DiscardLocals;
   bool DiscardNone;
   bool ExportDynamic;
   bool NoInhibitExec;
   bool NoUndefined;
+  bool Now = false;
   bool Shared;
   bool Static = false;
   bool WholeArchive = false;
 };
 
 extern Configuration *Config;
 
 } // namespace elf2
 } // namespace lld
 
 #endif

ELF/Driver.cpp

void LinkerDriver::link(ArrayRef<const char *> ArgsArr) {
   Config->DiscardAll = Args.hasArg(OPT_discard_all);
   Config->DiscardLocals = Args.hasArg(OPT_discard_locals);
   Config->DiscardNone = Args.hasArg(OPT_discard_none);
   Config->ExportDynamic = Args.hasArg(OPT_export_dynamic);
   Config->NoInhibitExec = Args.hasArg(OPT_noinhibit_exec);
   Config->NoUndefined = Args.hasArg(OPT_no_undefined);
   Config->Shared = Args.hasArg(OPT_shared);
 
+  for (auto *Arg : Args.filtered(OPT_z)) {
+    StringRef Opt = Arg->getValue();
+    if (Opt == "now")
+      Config->Now = true;
+    else {
+      warning(Twine("ignoring unknown argument for -z: ") + Opt);
+    }
+  }
+
   for (auto *Arg : Args) {
     switch (Arg->getOption().getID()) {
     case OPT_l:
       addFile(searchLibrary(Arg->getValue()));
       break;
     case OPT_INPUT:
       addFile(Arg->getValue());
       break;

ELF/Options.td

def sysroot : Joined<["--"], "sysroot=">,
   HelpText<"Set the system root">;
 
 def undefined : Joined<["--"], "undefined=">,
   HelpText<"Force undefined symbol during linking">;
 
 def whole_archive : Flag<["--"], "whole-archive">,
   HelpText<"Force load of all members in a static library">;
 
+def z : Separate<["-"], "z">, MetaVarName<"<option>">,
+  HelpText<"Linker option extensions">;
+
 // Aliases
 def alias_Bdynamic_call_shared: Flag<["-"], "call_shared">, Alias<Bdynamic>;
 def alias_Bdynamic_dy: Flag<["-"], "dy">, Alias<Bdynamic>;
 def alias_Bstatic_dn: Flag<["-"], "dn">, Alias<Bstatic>;
 def alias_Bstatic_non_shared: Flag<["-"], "non_shared">, Alias<Bstatic>;
 def alias_Bstatic_static: Flag<["-"], "static">, Alias<Bstatic>;
 def alias_L__library_path : Joined<["--"], "library-path=">, Alias<L>;
 def alias_discard_all_x: Flag<["-"], "x">, Alias<discard_all>;

 def hash_style : Joined<["--"], "hash-style=">;
 def m : Separate<["-"], "m">;
 def no_add_needed : Flag<["--"], "no-add-needed">;
 def no_as_needed : Flag<["--"], "no-as-needed">;
 def no_fatal_warnings : Flag<["--"], "no-fatal-warnings">;
 def start_group : Flag<["--"], "start-group">;
 def strip_all : Flag<["--"], "strip-all">;
 def version_script : Separate<["--"], "version-script">;
-def z : Separate<["-"], "z">;

ELF/OutputSections.cpp

template <class ELFT> void DynamicSection<ELFT>::finalize() {
   if (Symbol *S = SymTab.getSymbols().lookup(Config->Init))
     InitSym = dyn_cast<ELFSymbolBody<ELFT>>(S->Body);
   if (Symbol *S = SymTab.getSymbols().lookup(Config->Fini))
     FiniSym = dyn_cast<ELFSymbolBody<ELFT>>(S->Body);
   if (InitSym)
     ++NumEntries; // DT_INIT
   if (FiniSym)
     ++NumEntries; // DT_FINI
+  if (Config->Now)
+    ++NumEntries; // DT_FLAGS
 
   ++NumEntries; // DT_NULL
 
   Header.sh_size = NumEntries * Header.sh_entsize;
 }
 
 template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
   auto *P = reinterpret_cast<Elf_Dyn *>(Buf);
template <class ELFT> void DynamicSection<ELFT>::writeTo(uint8_t *Buf) {
   for (const std::unique_ptr<SharedFileBase> &File : SharedFiles)
     WriteVal(DT_NEEDED, DynStrSec.getFileOff(File->getSoName()));
 
   if (InitSym)
     WritePtr(DT_INIT, getSymVA(*InitSym, BssSec));
   if (FiniSym)
     WritePtr(DT_FINI, getSymVA(*FiniSym, BssSec));
 
+  uint32_t Flags = 0;
+  if (Config->Now)
+    Flags |= DF_1_NOW;
+  if (Flags)
+    WriteVal(DT_FLAGS_1, Flags);
+
   WriteVal(DT_NULL, 0);
 }
 
 template <class ELFT>
 OutputSection<ELFT>::OutputSection(const PltSection<ELFT> &PltSec,
                                    const GotSection<ELFT> &GotSec,
                                    const OutputSection<ELFT> &BssSec,
                                    StringRef Name, uint32_t sh_type,

test/elf2/now.s

+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t
+# RUN: lld -flavor gnu2 -shared %t -o %t.so
+# RUN: lld -flavor gnu2 -z now %t %t.so -o %t1
+# RUN: lld -flavor gnu2 %t %t.so -o %t2
+# RUN: llvm-readobj -dynamic-table %t1 | FileCheck -check-prefix=NOW %s
+# RUN: llvm-readobj -dynamic-table %t2 | FileCheck %s
+
+# NOW: DynamicSection [
+# NOW:   0x000000006FFFFFFB FLAGS_1 NOW
+# NOW: ]
+
+# CHECK: DynamicSection [
+# CHECK-NOT:   0x000000006FFFFFFB FLAGS_1 NOW
+# CHECK: ]
+
+.globl _start
+_start: