[lld-macho] Make everything PIE by default

[int3]

Summary

Modern versions of macOS (>= 10.7) and in general all modern Mach-O
target archs want PIEs by default. ld64 defaults to PIE for iOS >= 4.3,
as well as for all versions of watchOS and simulators. Basically all the
platforms LLD is likely to target want PIE. So instead of cluttering LLD's
code with legacy version checks, I think it's simpler to just default to
PIE for everything.

Note that -no_pie still works, so users can still opt out of it.

[thakis]

Makes sense. Maybe explicitly say in commit message that this only affects the default and that -no_pie still works.

[thakis]

Either this or https://github.com/llvm/llvm-project/commit/d9c8ffa958b7725e7d3a2231701ab20eb477b9ee – actually more likely the latter – breaks check-lld: http://45.33.8.238/linux/45432/step_11.txt

PTAL etc :)

[int3]

Whoops, accidentally git-added the wrong file

lld/MachO/Driver.cpp

 }
 
 static const char *getReproduceOption(InputArgList &args) {
   if (const Arg *arg = args.getLastArg(OPT_reproduce))
     return arg->getValue();
   return getenv("LLD_REPRODUCE");
 }
 
-static bool isPie(InputArgList &args) {
-  if (config->outputType != MH_EXECUTE || args.hasArg(OPT_no_pie))
-    return false;
-  if (config->arch() == AK_arm64 || config->arch() == AK_arm64e ||
-      config->arch() == AK_arm64_32)
-    return true;
-
-  // TODO: add logic here as we support more archs. E.g. i386 should default
-  // to PIE from 10.7
-  assert(config->arch() == AK_x86_64 || config->arch() == AK_x86_64h ||
-         config->arch() == AK_arm64_32);
-
-  PlatformKind kind = config->platformInfo.target.Platform;
-  if (kind == PlatformKind::macOS &&
-      config->platformInfo.minimum >= VersionTuple(10, 6))
-    return true;
-
-  if (kind == PlatformKind::iOSSimulator || kind == PlatformKind::driverKit)
-    return true;
-
-  return args.hasArg(OPT_pie);
-}
-
 static void parseClangOption(StringRef opt, const Twine &msg) {
   std::string err;
   raw_string_ostream os(err);
 
   const char *argv[] = {"lld", opt.data()};
   if (cl::ParseCommandLineOptions(2, argv, "", &os))
     return;
   os.flush();
#endif
 
   {
     TimeTraceScope timeScope("ExecuteLinker");
 
     initLLVM(); // must be run before any call to addFile()
     createFiles(args);
 
     config->isPic = config->outputType == MH_DYLIB ||
-                    config->outputType == MH_BUNDLE || isPie(args);
+                    config->outputType == MH_BUNDLE ||
+                    (config->outputType == MH_EXECUTE &&
+                     args.hasFlag(OPT_pie, OPT_no_pie, true));
 
     // Now that all dylibs have been loaded, search for those that should be
     // re-exported.
     {
       auto reexportHandler = [](const Arg *arg,
                                 const std::vector<StringRef> &extensions) {
         config->hasReexports = true;
         StringRef searchName = arg->getValue();

lld/MachO/Options.td

def dylib_current_version : Separate<["-"], "dylib_current_version">,
     Alias<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)">,
+    HelpText<"Build a position independent executable (default)">,
     Group<grp_main>;
 def no_pie : Flag<["-"], "no_pie">,
-    HelpText<"Do not build a position independent executable (default for macOS 10.6 and earlier)">,
+    HelpText<"Do not build a position independent executable">,
     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: llvm-objdump --macho --rebase %t-pie | FileCheck %s --check-prefix=PIE
 # RUN: %lld -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 -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
-# RUN: %lld -platform_version ios-simulator 11.0.0 14.2 -o %t-pie %t.o
-# RUN: llvm-objdump --macho --rebase %t-pie | FileCheck %s --check-prefix=PIE
-# RUN: %lld -platform_version driverkit 19.0 20.0 -o %t-pie %t.o
+# RUN: %lld -no_pie -pie -o %t-pie %t.o
 # RUN: llvm-objdump --macho --rebase %t-pie | FileCheck %s --check-prefix=PIE
 
 # CHECK:       Contents of section __DATA,foo:
 # CHECK-NEXT:  100001000 08100000 01000000
 # CHECK:       Contents of section __DATA,bar:
 # CHECK-NEXT:  100001008 011000f0 11211111 02000000
 
 # PIE:      Rebase table: