Implement --{push,pop}-state.

[ruiu]

Summary

--push-state implemented in this patch saves the states of --as-needed,
--whole-archive and --static. It saves less number of flags than GNU linkers.
Since even GNU linkers save different flags, no one seems to care about the
details. In this patch, I tried to save the minimal number of flags to not
complicate the implementation and the siutation.

I'm not personally happy to add the --{push,pop}-state flags though.
That options seem too hacky to me. However, gcc started using the options
since GCC 8 when GNU ld is available at the build time. Thererfore, lld
is no longer a drop-in replacmenet for GNU linker for that machine
without supporting the flags.

[grimar]

This is LGTM as is, but also added a suggestion about possible simplification.
I have no strong preference here though. I assume no much people will use this option anyways.

lld/ELF/Driver.cpp

944

One idea based on the difference of bfd and gold implementations.
As far I know, gold implements the true stack, but bfd - don't (https://sourceware.org/bugzilla/show_bug.cgi?id=18989#c2).
And letting users use the full power of nesting in invocations looks like a road to hell..

So should we just do it Optional<std::tuple<bool, bool, bool>> Stack?
Also, I would rename to State then.
(Or States if you decide to go with the true stack). It is consistent with the option name.

1032

Then it can be probably a bit simpler:

if (!Stack))
  error("--pop-state used without --push-state");
std::tie(Config->AsNeeded, Config->Static, InWholeArchive) =
  Stack.getValueOr(std::tuple<bool, bool, bool>());
break;

[ruiu]

lld/ELF/Driver.cpp

944

Looks like bfd linker at least can count the nesting depth. Are you sure that bfd cannot keep the stack of states?

$ ld.bfd --push-state --push-state --pop-state --pop-state
ld.bfd: no input files

$ ld.bfd --push-state --push-state --pop-state --pop-state --pop-state
ld.bfd: no state pushed before popping

[grimar]

lld/ELF/Driver.cpp

944

It just what that comment in their bugzilla seems was saying. But I did not check that.

[ruiu]

I don't know how it was implemented at the time when the bugzilla comment was posted, but it seems bfd linker's --push-state is a real stack now.

[grimar]

In D47542#1117552, @ruiu wrote:

I don't know how it was implemented at the time when the bugzilla comment was posted, but it seems bfd linker's --push-state is a real stack now.

Ok. Perhaps we should just follow then.

lld/ELF/Driver.cpp

static bool getBinaryOption(StringRef S) {
   if (S == "elf" || S == "default")
     return false;
   error("unknown -format value: " + S +
         " (supported formats: elf, default, binary)");
   return false;
 }
 
 void LinkerDriver::createFiles(opt::InputArgList &Args) {
+  // For --{push,pop}-state
+  std::vector<std::tuple<bool, bool, bool>> Stack;
+
+  // Iterate over argv to process input files and positional arguments.
   for (auto *Arg : Args) {
     switch (Arg->getOption().getUnaliasedOption().getID()) {
     case OPT_library:
       addLibrary(Arg->getValue());
       break;
     case OPT_INPUT:
       addFile(Arg->getValue(), /*WithLOption=*/false);
       break;
case OPT_start_lib:
       break;
     case OPT_end_lib:
       if (!InLib)
         error("stray --end-lib");
       InLib = false;
       InputFile::IsInGroup = false;
       ++InputFile::NextGroupId;
       break;
+    case OPT_push_state:
+      Stack.push_back({Config->AsNeeded, Config->Static, InWholeArchive});
+      break;
+    case OPT_pop_state:
+      if (Stack.empty()) {
+        error("unbalanced --push-state/--pop-state");
+        break;
+      }
+      std::tie(Config->AsNeeded, Config->Static, InWholeArchive) = Stack.back();
+      Stack.pop_back();
+      break;
     }
   }
 
   if (Files.empty() && errorCount() == 0)
     error("no input files");
 }
 
 // If -m <machine_type> was not given, infer it from object files.

lld/ELF/Options.td

 defm print_gc_sections: B<"print-gc-sections",
     "List removed unused sections",
     "Do not list removed unused sections">;
 
 defm print_icf_sections: B<"print-icf-sections",
     "List identical folded sections",
     "Do not list identical folded sections">;
 
+def pop_state: F<"pop-state">,
+  HelpText<"Undo the effect of -push-state">;
+
+def push_state: F<"push-state">,
+  HelpText<"Save the current state of -as-needed, -static and -whole-archive">;
+
 def print_map: F<"print-map">,
   HelpText<"Print a link map to the standard output">;
 
 defm reproduce: Eq<"reproduce">,
   HelpText<"Dump linker invocation and input files for debugging">;
 
 defm rpath: Eq<"rpath">, HelpText<"Add a DT_RUNPATH to the output">;
 

lld/docs/ld.lld.1

 .Dv a.out
 is used as a default.
 .It Fl -pie
 Create a position independent executable.
 .It Fl -print-gc-sections
 List removed unused sections.
 .It Fl -print-map
 Print a link map to the standard output.
+.It Fl -push-state
+Save the current state of
+.Fl -as-needed ,
+.Fl -static ,
+and
+.Fl -while-archive.
+.It Fl -pop-state
+Undo the effect of
+.Fl -push-state.
 .It Fl -relocatable
 Create relocatable object file.
 .It Fl -reproduce Ns = Ns Ar value
 Dump linker invocation and input files for debugging.
 .It Fl -retain-symbols-file Ns = Ns Ar file
 Retain only the symbols listed in the file.
 .It Fl -rpath Ns = Ns Ar value
 Add a

lld/test/ELF/push-state.s

+// REQUIRES: x86
+
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %s -o %t1.o
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux \
+// RUN:   %p/Inputs/whole-archive.s -o %t2.o
+// RUN: rm -f %t.a
+// RUN: llvm-ar rcs %t.a %t2.o
+
+// RUN: ld.lld -o %t.exe -push-state -whole-archive %t.a %t1.o -M | \
+// RUN:   FileCheck -check-prefix=WHOLE %s
+// WHOLE: _bar
+
+// RUN: ld.lld -o %t.exe -push-state -whole-archive -pop-state %t.a %t1.o -M | \
+// RUN:   FileCheck -check-prefix=NO-WHOLE %s
+// NO-WHOLE-NOT: _bar
+
+
+// RUN: llvm-mc -filetype=obj -triple=x86_64-unknown-linux %p/Inputs/shared.s -o %t3.o
+// RUN: ld.lld -shared %t3.o -soname libfoo -o %t.so
+
+// RUN: ld.lld -o %t.exe -push-state -as-needed %t.so %t1.o
+// RUN: llvm-readobj -dynamic-table %t.exe | FileCheck -check-prefix=AS-NEEDED %s
+// AS-NEEDED-NOT: NEEDED Shared library: [libfoo]
+
+// RUN: ld.lld -o %t.exe -push-state -as-needed -pop-state %t.so %t1.o
+// RUN: llvm-readobj -dynamic-table %t.exe | FileCheck -check-prefix=NO-AS-NEEDED %s
+// NO-AS-NEEDED: NEEDED Shared library: [libfoo]
+
+
+// RUN: mkdir -p %t.dir
+// RUN: cp %t.so %t.dir/libfoo.so
+// RUN: ld.lld -o %t.exe -L%t.dir -push-state -static -pop-state  %t1.o -lfoo
+// RUN: not ld.lld -o %t.exe -L%t.dir -push-state -static %t1.o -lfoo
+
+.globl _start
+_start: