[lld-macho] Extend PIE option handling

[int3]

Summary

• Enable PIE by default if targeting 10.6 or above on x86-64. (The manpage says 10.7, but that actually applies only to i386, and in general varies based on the target platform. I didn't update the manpage because listing all the different behaviors would make for a pretty long description.)
• Add support for -no_pie
• Remove HelpHidden from -pie

[thakis]

Thanks!

lld/MachO/Driver.cpp

 }
 
 static const char *getReproduceOption(opt::InputArgList &args) {
   if (auto *arg = args.getLastArg(OPT_reproduce))
     return arg->getValue();
   return getenv("LLD_REPRODUCE");
 }
 
+static bool isPie(opt::InputArgList &args) {
+  if (config->outputType != MH_EXECUTE || args.hasArg(OPT_no_pie))
+    return false;
+
+  // TODO: add logic here as we support more archs. E.g. i386 should default
+  // to PIE from 10.7, arm64 should always be PIE, etc
+  assert(config->arch == AK_x86_64 || config->arch == AK_x86_64h);
+
+  if (config->platform.kind == MachO::PlatformKind::macOS &&
+      config->platform.minimum >= VersionTuple(10, 6))
+    return true;
+
+  return args.hasArg(OPT_pie);
+}
+
 bool macho::link(llvm::ArrayRef<const char *> argsArr, bool canExitEarly,
                  raw_ostream &stdoutOS, raw_ostream &stderrOS) {
   lld::stdoutOS = &stdoutOS;
   lld::stderrOS = &stderrOS;
 
   stderrOS.enable_colors(stderrOS.has_colors());
   // TODO: Set up error handler properly, e.g. the errorLimitExceededMsg
 
case OPT_platform_version:
       handlePlatformVersion(arg);
       break;
     default:
       break;
     }
   }
 
   config->isPic = config->outputType == MH_DYLIB ||
-                  config->outputType == MH_BUNDLE ||
-                  (config->outputType == MH_EXECUTE && args.hasArg(OPT_pie));
+                  config->outputType == MH_BUNDLE || isPie(args);
 
   // Now that all dylibs have been loaded, search for those that should be
   // re-exported.
   for (opt::Arg *arg : args.filtered(OPT_sub_library)) {
     config->hasReexports = true;
     StringRef searchName = arg->getValue();
     if (!markSubLibrary(searchName))
       error("-sub_library " + searchName + " does not match a supplied dylib");

lld/MachO/Options.td

def dylib_current_version : Separate<["-"], "dylib_current_version">,
      HelpText<"Alias for -current_version">,
      Flags<[HelpHidden]>,
      Group<grp_dylib>;
 
 def grp_main : OptionGroup<"main">, HelpText<"MAIN EXECUTABLE">;
 
 def pie : Flag<["-"], "pie">,
      HelpText<"Build a position independent executable (default for macOS 10.7 and later)">,
-     Flags<[HelpHidden]>,
      Group<grp_main>;
 def no_pie : Flag<["-"], "no_pie">,
      HelpText<"Do not build a position independent executable (default for macOS 10.6 and earlier)">,
-     Flags<[HelpHidden]>,
      Group<grp_main>;
 def pagezero_size : Separate<["-"], "pagezero_size">,
      MetaVarName<"<size>">,
      HelpText<"Size of unreadable segment at address zero is hex <size> (default is 4KB on 32-bit and 4GB on 64-bit)">,
      Flags<[HelpHidden]>,
      Group<grp_main>;
 def stack_size : Separate<["-"], "stack_size">,
      MetaVarName<"<size>">,

lld/test/MachO/x86-64-reloc-unsigned.s

 # REQUIRES: x86
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
 # RUN: %lld -o %t %t.o
 # RUN: llvm-objdump --macho --rebase --full-contents %t | FileCheck %s
 
-# RUN: %lld -pie -o %t-pie %t.o
+# RUN: %lld -fatal_warnings -pie -o %t-pie %t.o
 # RUN: llvm-objdump --macho --rebase %t-pie | FileCheck %s --check-prefix=PIE
+# RUN: %lld -fatal_warnings -pie -no_pie -o %t-no-pie %t.o
+# RUN: llvm-objdump --macho --rebase %t-no-pie | FileCheck %s --check-prefix=NO-PIE
+# RUN: %lld -fatal_warnings -no_pie -pie -o %t-no-pie %t.o
+# RUN: llvm-objdump --macho --rebase %t-no-pie | FileCheck %s --check-prefix=NO-PIE
+
+# RUN: %lld -platform_version macos 10.6.0 11.0 -o %t-pie %t.o
+# RUN: llvm-objdump --macho --rebase %t-pie | FileCheck %s --check-prefix=PIE
+# RUN: %lld -platform_version macos 10.5.0 11.0 -o %t-no-pie %t.o
+# RUN: llvm-objdump --macho --rebase %t-no-pie | FileCheck %s --check-prefix=NO-PIE
 
 # CHECK:       Contents of section __DATA,foo:
 # CHECK-NEXT:  100001000 08100000 01000000
 # CHECK:       Contents of section __DATA,bar:
 # CHECK-NEXT:  100001008 011000f0 11211111 02000000
 # CHECK:       Rebase table:
 # CHECK-NEXT:  segment  section            address     type
 # CHECK-EMPTY:
 
 # PIE:      Rebase table:
 # PIE-NEXT: segment  section            address           type
 # PIE-DAG:  __DATA   foo                0x[[#%X,ADDR:]]   pointer
 # PIE-DAG:  __DATA   bar                0x[[#ADDR + 8]]   pointer
 # PIE-DAG:  __DATA   bar                0x[[#ADDR + 12]]  pointer
 # PIE-DAG:  __DATA   baz                0x[[#ADDR + 20]]  pointer
 
+# NO-PIE:      Rebase table:
+# NO-PIE-NEXT: segment  section            address           type
+# NO-PIE-EMPTY:
+
 .globl _main, _foo, _bar
 
 .section __DATA,foo
 _foo:
 .quad _bar
 
 .section __DATA,bar
 _bar: