macho/load_commands: support new macOS 15 dylib use command (#625)

Author: Bo98

.gitignore

@@ -22,3 +22,6 @@
 .ruby-version
 .idea/
 .vscode/
+
+# macOS metadata file
+.DS_Store

lib/macho/load_commands.rb

@@ -111,7 +111,7 @@ module LoadCommands
       # "reserved for internal use only", no public struct
       :LC_PREPAGE => "LoadCommand",
       :LC_DYSYMTAB => "DysymtabCommand",
-      :LC_LOAD_DYLIB => "DylibCommand",
+      :LC_LOAD_DYLIB => "DylibUseCommand",
       :LC_ID_DYLIB => "DylibCommand",
       :LC_LOAD_DYLINKER => "DylinkerCommand",
       :LC_ID_DYLINKER => "DylinkerCommand",
@@ -123,7 +123,7 @@ module LoadCommands
       :LC_SUB_LIBRARY => "SubLibraryCommand",
       :LC_TWOLEVEL_HINTS => "TwolevelHintsCommand",
       :LC_PREBIND_CKSUM => "PrebindCksumCommand",
-      :LC_LOAD_WEAK_DYLIB => "DylibCommand",
+      :LC_LOAD_WEAK_DYLIB => "DylibUseCommand",
       :LC_SEGMENT_64 => "SegmentCommand64",
       :LC_ROUTINES_64 => "RoutinesCommand64",
       :LC_UUID => "UUIDCommand",
@@ -195,6 +195,20 @@ module LoadCommands
       :SG_READ_ONLY => 0x10,
     }.freeze
 
+    # association of dylib use flag symbols to values
+    # @api private
+    DYLIB_USE_FLAGS = {
+      :DYLIB_USE_WEAK_LINK => 0x1,
+      :DYLIB_USE_REEXPORT => 0x2,
+      :DYLIB_USE_UPWARD => 0x4,
+      :DYLIB_USE_DELAYED_INIT => 0x8,
+    }.freeze
+
+    # the marker used to denote a newer style dylib use command.
+    # the value is the timestamp 24 January 1984 18:12:16
+    # @api private
+    DYLIB_USE_MARKER = 0x1a741800
+
     # The top-level Mach-O load command structure.
     #
     # This is the most generic load command -- only the type ID and size are
@@ -233,6 +247,13 @@ def self.create(cmd_sym, *args)
         # cmd will be filled in, view and cmdsize will be left unpopulated
         klass_arity = klass.min_args - 3
 
+        # macOS 15 introduces a new dylib load command that adds a flags field to the end.
+        # It uses the same commands with it dynamically being created if the dylib has a flags field
+        if klass == DylibUseCommand && (args[1] != DYLIB_USE_MARKER || args.size <= DylibCommand.min_args - 3)
+          klass = DylibCommand
+          klass_arity = klass.min_args - 3
+        end
+
         raise LoadCommandCreationArityError.new(cmd_sym, klass_arity, args.size) if klass_arity > args.size
 
         klass.new(nil, cmd, nil, *args)
@@ -528,6 +549,23 @@ class DylibCommand < LoadCommand
       # @return [Integer] the library's compatibility version number
       field :compatibility_version, :uint32
 
+      # @example
+      #  puts "this dylib is weakly loaded" if dylib_command.flag?(:DYLIB_USE_WEAK_LINK)
+      # @param flag [Symbol] a dylib use command flag symbol
+      # @return [Boolean] true if `flag` applies to this dylib command
+      def flag?(flag)
+        case cmd
+        when LOAD_COMMAND_CONSTANTS[:LC_LOAD_WEAK_DYLIB]
+          flag == :DYLIB_USE_WEAK_LINK
+        when LOAD_COMMAND_CONSTANTS[:LC_REEXPORT_DYLIB]
+          flag == :DYLIB_USE_REEXPORT
+        when LOAD_COMMAND_CONSTANTS[:LC_LOAD_UPWARD_DYLIB]
+          flag == :DYLIB_USE_UPWARD
+        else
+          false
+        end
+      end
+
       # @param context [SerializationContext]
       #  the context
       # @return [String] the serialized fields of the load command
@@ -553,6 +591,65 @@ def to_h
       end
     end
 
+    # The newer format of load command representing some aspect of shared libraries,
+    # depending on filetype. Corresponds to LC_LOAD_DYLIB or LC_LOAD_WEAK_DYLIB.
+    class DylibUseCommand < DylibCommand
+      # @return [Integer] any flags associated with this dylib use command
+      field :flags, :uint32
+
+      alias marker timestamp
+
+      # Instantiates a new DylibCommand or DylibUseCommand.
+      # macOS 15 and later use a new format for dylib commands (DylibUseCommand),
+      # which is determined based on a special timestamp and the name offset.
+      # @param view [MachO::MachOView] the load command's raw view
+      # @return [DylibCommand] the new dylib load command
+      # @api private
+      def self.new_from_bin(view)
+        dylib_command = DylibCommand.new_from_bin(view)
+
+        if dylib_command.timestamp == DYLIB_USE_MARKER &&
+           dylib_command.name.to_i == DylibUseCommand.bytesize
+          super(view)
+        else
+          dylib_command
+        end
+      end
+
+      # @example
+      #  puts "this dylib is weakly loaded" if dylib_command.flag?(:DYLIB_USE_WEAK_LINK)
+      # @param flag [Symbol] a dylib use command flag symbol
+      # @return [Boolean] true if `flag` applies to this dylib command
+      def flag?(flag)
+        flag = DYLIB_USE_FLAGS[flag]
+
+        return false if flag.nil?
+
+        flags & flag == flag
+      end
+
+      # @param context [SerializationContext]
+      #  the context
+      # @return [String] the serialized fields of the load command
+      # @api private
+      def serialize(context)
+        format = Utils.specialize_format(self.class.format, context.endianness)
+        string_payload, string_offsets = Utils.pack_strings(self.class.bytesize,
+                                                            context.alignment,
+                                                            :name => name.to_s)
+        cmdsize = self.class.bytesize + string_payload.bytesize
+        [cmd, cmdsize, string_offsets[:name], marker, current_version,
+         compatibility_version, flags].pack(format) + string_payload
+      end
+
+      # @return [Hash] a hash representation of this {DylibUseCommand}
+      def to_h
+        {
+          "flags" => flags,
+        }.merge super
+      end
+    end
+
     # A load command representing some aspect of the dynamic linker, depending
     # on filetype. Corresponds to LC_ID_DYLINKER, LC_LOAD_DYLINKER, and
     # LC_DYLD_ENVIRONMENT.

test/bin/x86_64/dylib_use_command-weak-delay.bin

@@ -1,6 +1,7 @@
 # Usage:
 #   make USE=10.6-xcode3.2.6
 #   make USE=10.11-xcode7.3
+#   make USE=15-xcode16.0
 
 HELLO_SRC    = hello.c
 LIBHELLO_SRC = libhello.c
@@ -42,13 +43,24 @@ else ifeq ($(USE),10.6-xcode3.2.6)
   USE_DIRS := i386 x86_64 ppc fat-i386-x86_64 fat-i386-ppc
   NO_UPWARD := 1
   NO_LAZY := 1
+  NO_DELAY_INIT := 1
 else ifeq ($(USE),10.11-xcode7.3)
   USE_DIRS := i386 x86_64 fat-i386-x86_64
+  NO_DELAY_INIT := 1
+else ifeq ($(USE),15-xcode16.0)
+  USE_DIRS := x86_64
+  NO_LAZY := 1
 else
   # Warn about unspecified subset, but effectively fall back to 10.11-xcode7.3.
   $(warning USE - Option either unset or invalid. Using a safe fallback.)
-  $(warning USE - Valid choices: all, 10.6-xcode3.2.6, 10.11-xcode7.3.)
+  $(warning USE - Valid choices: all, 10.6-xcode3.2.6, 10.11-xcode7.3, 15-xcode16.0.)
   USE_DIRS := i386 x86_64 fat-i386-x86_64
+  NO_DELAY_INIT := 1
+  NO_LAZY := 1
+endif
+
+ifeq ($(NO_DELAY_INIT),)
+  TARGET_FILES += dylib_use_command-weak-delay.bin
 endif
 
 # Setup target names from all/used architecture directories.
@@ -84,10 +96,10 @@ $(ALL_DIRS):
 
 # Setup architecture-specific per-file targets (`<arch>/<file>`).
 %/hello.o: $(HELLO_SRC) %
-	$(CC) $(ARCH_FLAGS) -o $@ -c $<
+	$(CC) $(CFLAGS) $(ARCH_FLAGS) -o $@ -c $<
 
 %/hello.bin: $(HELLO_SRC) %
-	$(CC) $(ARCH_FLAGS) -o $@ $(RPATH_FLAGS) $<
+	$(CC) $(CFLAGS) $(ARCH_FLAGS) -o $@ $(RPATH_FLAGS) $<
 
 %/hello_expected.bin: %/hello.bin
 	cp $< $@
@@ -97,18 +109,21 @@ $(ALL_DIRS):
 	cp $< $@
 	install_name_tool -rpath made_up_path /usr/lib $@
 
+%/dylib_use_command-weak-delay.bin: $(HELLO_SRC) %
+	$(CC) $(CFLAGS) $(ARCH_FLAGS) -o $@ -Wl,-weak-l,z -Wl,-delay-l,z $<
+
 %/libhello.dylib: $(LIBHELLO_SRC) %
-	$(CC) $(ARCH_FLAGS) -o $@ -dynamiclib $<
+	$(CC) $(CFLAGS) $(ARCH_FLAGS) -o $@ -dynamiclib $<
 
 %/libhello_expected.dylib: %/libhello.dylib
 	cp $< $@
 	install_name_tool -id test $@
 
 %/libextrahello.dylib: $(LIBHELLO_SRC) % %/libhello.dylib
-	$(CC) $(ARCH_FLAGS) -o $@ -dynamiclib $< $(LIBEXTRA_LDADD)
+	$(CC) $(CFLAGS) $(ARCH_FLAGS) -o $@ -dynamiclib $< $(LIBEXTRA_LDADD)
 
 %/hellobundle.so: $(LIBHELLO_SRC) %
-	$(CC) $(ARCH_FLAGS) -bundle $< -o $@
+	$(CC) $(CFLAGS) $(ARCH_FLAGS) -bundle $< -o $@
 
 # build inconsistent binaries
 .PHONY: inconsistent

test/src/Makefile

@@ -24,7 +24,7 @@ def test_create_dylib_commands
       lc = MachO::LoadCommands::LoadCommand.create(cmd_sym, "test", 0, 0, 0)
 
       assert lc
-      assert_kind_of MachO::LoadCommands::DylibCommand, lc
+      assert_instance_of MachO::LoadCommands::DylibCommand, lc
       assert lc.name
       assert_kind_of MachO::LoadCommands::LoadCommand::LCStr, lc.name
       assert_equal "test", lc.name.to_s
@@ -36,6 +36,26 @@ def test_create_dylib_commands
     end
   end
 
+  def test_create_dylib_commands_new
+    # all dylib commands are creatable, so test them all
+    dylib_commands = %i[LC_LOAD_DYLIB LC_LOAD_WEAK_DYLIB]
+    dylib_commands.each do |cmd_sym|
+      lc = MachO::LoadCommands::LoadCommand.create(cmd_sym, "test", MachO::LoadCommands::DYLIB_USE_MARKER, 0, 0, 0)
+
+      assert lc
+      assert_instance_of MachO::LoadCommands::DylibUseCommand, lc
+      assert lc.name
+      assert_kind_of MachO::LoadCommands::LoadCommand::LCStr, lc.name
+      assert_equal "test", lc.name.to_s
+      assert_equal lc.name.to_s, lc.to_s
+      assert_equal MachO::LoadCommands::DYLIB_USE_MARKER, lc.timestamp
+      assert_equal 0, lc.current_version
+      assert_equal 0, lc.compatibility_version
+      assert_equal 0, lc.flags
+      assert_instance_of String, lc.view.inspect
+    end
+  end
+
   def test_create_rpath_command
     lc = MachO::LoadCommands::LoadCommand.create(:LC_RPATH, "test")
 

test/test_create_load_commands.rb

@@ -235,20 +235,20 @@ def test_dylib
 
   def test_extra_dylib
     filenames = SINGLE_ARCHES.map { |a| fixture(a, "libextrahello.dylib") }
-    unusual_dylib_lcs = %i[
-      LC_LOAD_UPWARD_DYLIB
-      LC_LAZY_LOAD_DYLIB
-      LC_LOAD_WEAK_DYLIB
-      LC_REEXPORT_DYLIB
-    ]
+    unusual_dylib_lcs = {
+      LC_LOAD_UPWARD_DYLIB: :DYLIB_USE_UPWARD,
+      LC_LAZY_LOAD_DYLIB: nil,
+      LC_LOAD_WEAK_DYLIB: :DYLIB_USE_WEAK_LINK,
+      LC_REEXPORT_DYLIB: :DYLIB_USE_REEXPORT,
+    }
 
     filenames.each do |fn|
       file = MachO::MachOFile.new(fn)
 
       assert file.dylib?
 
       # make sure we can read more unusual dylib load commands
-      unusual_dylib_lcs.each do |cmdname|
+      unusual_dylib_lcs.each do |cmdname, flag_name|
         lc = file[cmdname].first
 
         # PPC and x86-family binaries don't have the same dylib LCs, so ignore
@@ -262,10 +262,37 @@ def test_extra_dylib
 
         assert dylib_name
         assert_kind_of MachO::LoadCommands::LoadCommand::LCStr, dylib_name
+
+        assert lc.flag?(flag_name) if flag_name
+        (unusual_dylib_lcs.values - [flag_name]).compact.each do |other_flag_name|
+          refute lc.flag?(other_flag_name)
+        end
       end
     end
   end
 
+  def test_dylib_use_command
+    filenames = SINGLE_64_ARCHES.map { |a| fixture(a, "dylib_use_command-weak-delay.bin") }
+
+    filenames.each do |fn|
+      file = MachO::MachOFile.new(fn)
+
+      lc = file[:LC_LOAD_WEAK_DYLIB].first
+      lc2 = file[:LC_LOAD_DYLIB].first
+
+      assert_instance_of MachO::LoadCommands::DylibUseCommand, lc
+      assert_instance_of MachO::LoadCommands::DylibCommand, lc2
+
+      refute_equal lc.flags, 0
+
+      assert lc.flag?(:DYLIB_USE_WEAK_LINK)
+      assert lc.flag?(:DYLIB_USE_DELAYED_INIT)
+      refute lc.flag?(:DYLIB_USE_UPWARD)
+
+      refute lc2.flag?(:DYLIB_USE_WEAK_LINK)
+    end
+  end
+
   def test_bundle
     filenames = SINGLE_ARCHES.map { |a| fixture(a, "hellobundle.so") }
 

test/test_macho.rb

@@ -69,6 +69,25 @@ def test_serialize_load_dylib
                                                     lc.compatibility_version)
       blob = lc.view.raw_data[lc.view.offset, lc.cmdsize]
 
+      assert_instance_of lc.class, lc2
+      assert_equal blob, lc.serialize(ctx)
+      assert_equal blob, lc2.serialize(ctx)
+    end
+  end
+
+  def test_serialize_load_dylib_new
+    filenames = SINGLE_64_ARCHES.map { |a| fixture(a, "dylib_use_command-weak-delay.bin") }
+
+    filenames.each do |filename|
+      file = MachO::MachOFile.new(filename)
+      ctx = MachO::LoadCommands::LoadCommand::SerializationContext.context_for(file)
+      lc = file[:LC_LOAD_WEAK_DYLIB].first
+      lc2 = MachO::LoadCommands::LoadCommand.create(:LC_LOAD_WEAK_DYLIB, lc.name.to_s,
+                                                    lc.marker, lc.current_version,
+                                                    lc.compatibility_version, lc.flags)
+      blob = lc.view.raw_data[lc.view.offset, lc.cmdsize]
+
+      assert_instance_of lc.class, lc2
       assert_equal blob, lc.serialize(ctx)
       assert_equal blob, lc2.serialize(ctx)
     end