[llvm] strip code signature load commands with llvm-bitcode-strip

[rmaz]

Summary

This diff adds stripping of LC_CODE_SIGNATURE load commands with
llvm-bitcode-strip by default. The -keep_cs flag is added to
preserve code signature load commands.

[rmaz]

It looks like we don't need this change as code signature updating was implemented in D111164. Verified with:

% llvm-bitcode-strip -r -keep_cs libswiftCore.dylib -o stripped.dylib
% codesign -v -vvv stripped.dylib
stripped.dylib: valid on disk
stripped.dylib: satisfies its Designated Requirement

llvm/include/llvm/ObjCopy/MachO/MachOConfig.h

struct MachOConfig {
   DenseSet<StringRef> RPathsToRemove;
 
   // install-name-tool's id option
   Optional<StringRef> SharedLibId;
 
   // Boolean options
   bool StripSwiftSymbols = false;
   bool KeepUndefined = false;
+  bool RemoveCodesignLoadCommands = false;
 
   // install-name-tool's --delete_all_rpaths
   bool RemoveAllRpaths = false;
 };
 
 } // namespace objcopy
 } // namespace llvm
 
 #endif // LLVM_OBJCOPY_MACHO_MACHOCONFIG_H

llvm/lib/ObjCopy/MachO/MachOObjcopy.cpp

 //===- MachOObjcopy.cpp -----------------------------------------*- C++ -*-===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/ObjCopy/MachO/MachOObjcopy.h"
 #include "Archive.h"
 #include "MachOReader.h"
 #include "MachOWriter.h"
 #include "llvm/ADT/DenseSet.h"
+#include "llvm/BinaryFormat/MachO.h"
 #include "llvm/ObjCopy/CommonConfig.h"
 #include "llvm/ObjCopy/MachO/MachOConfig.h"
 #include "llvm/ObjCopy/MultiFormatConfig.h"
 #include "llvm/ObjCopy/ObjCopy.h"
 #include "llvm/Object/ArchiveWriter.h"
 #include "llvm/Object/MachOUniversal.h"
 #include "llvm/Object/MachOUniversalWriter.h"
 #include "llvm/Support/Errc.h"
Obj.LoadCommands.insert(Obj.LoadCommands.begin(),
                             buildRPathLoadCommand(RPath));
   }
 
   // Unlike appending rpaths, the indexes of subsequent load commands must
   // be recalculated after prepending one.
   if (!MachOConfig.RPathToPrepend.empty())
     Obj.updateLoadCommandIndexes();
 
+  // Remove codesign load commands.
+  if (MachOConfig.RemoveCodesignLoadCommands) {
+    auto RemovePred = [](const LoadCommand &LC) {
+      return LC.MachOLoadCommand.load_command_data.cmd ==
+             MachO::LC_CODE_SIGNATURE;
+    };
+    if (Error E = Obj.removeLoadCommands(RemovePred))
+      return E;
+  }
+
   return Error::success();
 }
 
 static Error dumpSectionToFile(StringRef SecName, StringRef Filename,
                                Object &Obj) {
   for (LoadCommand &LC : Obj.LoadCommands)
     for (const std::unique_ptr<Section> &Sec : LC.Sections) {
       if (Sec->CanonicalName == SecName) {

llvm/test/tools/llvm-objcopy/MachO/bitcode-strip-codesign.test

+## Test codesign load commands are stripped by default.
+# RUN: yaml2obj %s -o %t
+# RUN: llvm-bitcode-strip -r %t -o %t2
+# RUN: llvm-otool -l %t2 | FileCheck --check-prefix=NOCODESIGN %s
+
+# NOCODESIGN-NOT: LC_CODE_SIGNATURE
+
+## Test codesign load commands are kept with -keep_cs.
+# RUN: llvm-bitcode-strip -keep_cs -r %t -o %t3
+# RUN: llvm-otool -l %t3 | FileCheck --check-prefix=CODESIGN %s
+
+# CODESIGN: LC_CODE_SIGNATURE
+
+--- !mach-o
+FileHeader:
+  magic:           0xFEEDFACF
+  cputype:         0x01000007
+  cpusubtype:      0x00000003
+  filetype:        0x00000001
+  ncmds:           2
+  sizeofcmds:      168
+  flags:           0x00002000
+  reserved:        0x00000000
+LoadCommands:
+  - cmd:             LC_SEGMENT_64
+    cmdsize:         152
+    segname:         __TEXT
+    vmaddr:          0
+    vmsize:          4
+    fileoff:         200
+    filesize:        4
+    maxprot:         7
+    initprot:        7
+    nsects:          1
+    flags:           0
+    Sections:
+      - sectname:        __text
+        segname:         __TEXT
+        addr:            0x0000000000000000
+        content:         'AABBCCDD'
+        size:            4
+        offset:          200
+        align:           0
+        reloff:          0x00000000
+        nreloc:          0
+        flags:           0x80000400
+        reserved1:       0x00000000
+        reserved2:       0x00000000
+        reserved3:       0x00000000
+  - cmd:            LC_CODE_SIGNATURE
+    cmdsize:        16
+    dataoff:        0
+    datasize:       0

llvm/tools/llvm-objcopy/BitcodeStripOpts.td

 
 def V : Flag<["-"], "V">,
         Alias<version>,
         HelpText<"Alias for --version">;
 
 def remove : Flag<["-"], "r">,
         HelpText<"Remove the __LLVM bitcode segment entirely">;
 
+def keep_codesign : Flag<["-"], "keep_cs">,
+        HelpText<"Preserve the codesign load commands in the output binary, even though the code signature is no longer valid">;
+
 def output : JoinedOrSeparate<["-"], "o">, HelpText<"Write output to <file>">,
              MetaVarName<"<file>">;

llvm/tools/llvm-objcopy/ObjcopyOptions.cpp

 }
 
 Expected<DriverConfig>
 objcopy::parseBitcodeStripOptions(ArrayRef<const char *> ArgsArr,
                                   function_ref<Error(Error)> ErrorCallback) {
   DriverConfig DC;
   ConfigManager ConfigMgr;
   CommonConfig &Config = ConfigMgr.Common;
+  MachOConfig &MachOConfig = ConfigMgr.MachO;
   BitcodeStripOptTable T;
   unsigned MissingArgumentIndex, MissingArgumentCount;
   opt::InputArgList InputArgs =
       T.ParseArgs(ArgsArr, MissingArgumentIndex, MissingArgumentCount);
 
   if (InputArgs.size() == 0) {
     printHelp(T, errs(), ToolType::BitcodeStrip);
     exit(1);
objcopy::parseBitcodeStripOptions(ArrayRef<const char *> ArgsArr,
 
   if (!InputArgs.hasArg(BITCODE_STRIP_remove))
     return createStringError(errc::invalid_argument, "no action specified");
 
   // We only support -r for now, which removes all bitcode sections.
   cantFail(Config.ToRemove.addMatcher(NameOrPattern::create(
       "__LLVM,__bundle", MatchStyle::Literal, ErrorCallback)));
 
+  // By default remove codesign load commands as they will be invalid after
+  // stripping.
+  MachOConfig.RemoveCodesignLoadCommands =
+      !InputArgs.hasArg(BITCODE_STRIP_keep_codesign);
+
   DC.CopyConfigs.push_back(std::move(ConfigMgr));
   return std::move(DC);
 }
 
 // ParseStripOptions returns the config and sets the input arguments. If a
 // help flag is set then ParseStripOptions will print the help messege and
 // exit.
 Expected<DriverConfig>