[lld] [lld-macho] Implement support for ObjC relative method lists (PR #86231)

[Kyungwoo Lee via llvm-commits]

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+# REQUIRES: aarch64
+# RUN: rm -rf %t; split-file %s %t && cd %t
+
+## Compile a64_rel_dylib.o
+# RUN: llvm-mc -filetype=obj -triple=arm64-apple-macos -o a64_rel_dylib.o a64_simple_class.s
+
+## Test arm64 + relative method lists
+# RUN: %no-lsystem-lld a64_rel_dylib.o -o a64_rel_dylib.dylib -map a64_rel_dylib.map -dylib -arch arm64 -objc_relative_method_lists
+# RUN: llvm-objdump --macho --objc-meta-data a64_rel_dylib.dylib  | FileCheck %s --check-prefix=CHK_REL
+
+## Test arm64 + traditional method lists (no relative offsets)
+# RUN: %no-lsystem-lld a64_rel_dylib.o -o a64_rel_dylib.dylib -map a64_rel_dylib.map -dylib -arch arm64 -no_objc_relative_method_lists
+# RUN: llvm-objdump --macho --objc-meta-data a64_rel_dylib.dylib  | FileCheck %s --check-prefix=CHK_NO_REL
+
+
+CHK_REL:       Contents of (__DATA_CONST,__objc_classlist) section
+CHK_REL-NEXT:  _OBJC_CLASS_$_MyClass
+CHK_REL:       baseMethods
+CHK_REL-NEXT:  entsize 24 (relative)
+CHK_REL-NEXT:  count 3
+CHK_REL-NEXT:   name 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) instance_method_00
+CHK_REL-NEXT:  types 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) v16 at 0:8
+CHK_REL-NEXT:    imp 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) -[MyClass instance_method_00]
+CHK_REL-NEXT:   name 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) instance_method_01
+CHK_REL-NEXT:  types 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) v16 at 0:8
+CHK_REL-NEXT:    imp 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) -[MyClass instance_method_01]
+CHK_REL-NEXT:   name 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) instance_method_02
+CHK_REL-NEXT:  types 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) v16 at 0:8
+CHK_REL-NEXT:    imp 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}}) -[MyClass instance_method_02]
+
+CHK_REL:       Meta Class
+CHK_REL-NEXT:  isa 0x{{[0-9a-f]*}} _OBJC_METACLASS_$_MyClass
+CHK_REL:       baseMethods 0x694 (struct method_list_t *)
+CHK_REL-NEXT:  entsize 24 (relative)
+CHK_REL-NEXT:  count 3
+CHK_REL-NEXT:   name 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  class_method_00
+CHK_REL-NEXT:  types 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  v16 at 0:8
+CHK_REL-NEXT:    imp 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  +[MyClass class_method_00]
+CHK_REL-NEXT:   name 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  class_method_01
+CHK_REL-NEXT:  types 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  v16 at 0:8
+CHK_REL-NEXT:    imp 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  +[MyClass class_method_01]
+CHK_REL-NEXT:   name 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  class_method_02
+CHK_REL-NEXT:  types 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  v16 at 0:8
+CHK_REL-NEXT:    imp 0x{{[0-9a-f]*}} (0x{{[0-9a-f]*}})  +[MyClass class_method_02]
+
+
+CHK_NO_REL-NOT: (relative)
+
+CHK_NO_REL:           Contents of (__DATA_CONST,__objc_classlist) section
+CHK_NO_REL-NEXT:      _OBJC_CLASS_$_MyClass
+
+CHK_NO_REL:            baseMethods 0x80e8 (struct method_list_t *)
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kyulee-com wrote:

Not sure if addresses are constant, but you might want to relax it using a regex like the case with relative method list.

https://github.com/llvm/llvm-project/pull/86231