[lld/macho] Fixes the -ObjC flag

[tt]

Summary

When checking the segment name for Swift symbols, we should be checking that they start with __swift instead of checking for equality

Fixes the issue https://github.com/llvm/llvm-project/issues/55355

[keith]

Which sections specifically hit this? can you add a test?

[tt]

I see this happening for __swift5_proto but yes, will add a test

There are several __swift* sections, in fact, I haven't run into a __swift section at all.
For e.g. compiling the following code results into sections:

protocol Blah {}
extension Blah {
    func foobar() {
    }
}
func noop() {}

/tmp/Blah.o:	file format mach-o 64-bit x86-64

Sections:
Idx Name             Size     VMA              Type
  0 __text           00000026 0000000000000000 TEXT
  1 __swift5_entry   00000004 0000000000000028 DATA
  2 __swift5_typeref 0000000b 000000000000002c DATA
  3 __swift5_fieldmd 00000010 0000000000000038 DATA
  4 __const          0000002e 0000000000000048 DATA
  5 __swift5_protos  00000004 0000000000000078 DATA
  6 __swift_modhash  00000010 000000000000007c DATA
  7 __objc_imageinfo 00000008 000000000000008c DATA
  8 __compact_unwind 00000060 0000000000000098 DATA
  9 __eh_frame       00000090 00000000000000f8 DATA

SYMBOL TABLE:
0000000000000028 l     O __TEXT,__swift5_entry l_entry_point
0000000000000038 l     O __TEXT,__swift5_fieldmd _$s4BlahAA_pMF
0000000000000048 l     O __TEXT,__const l___unnamed_1
0000000000000078 l     O __TEXT,__swift5_protos l_protocols
000000000000007c l     O __LLVM,__swift_modhash l_llvm.swift_module_hash
0000000000000020 g     F __TEXT,__text _$s4Blah4noopyyF
000000000000005c g     O __TEXT,__const _$s4BlahAAMp
0000000000000010 g     F __TEXT,__text _$s4BlahAAPAAE6foobaryyF
0000000000000050  w    O __TEXT,__const _$s4BlahMXM
0000000000000074  w    O __TEXT,__const ___swift_reflection_version
0000000000000000 g     F __TEXT,__text _main
000000000000002c  w    O __TEXT,__swift5_typeref _symbolic $s4BlahAAP

[tt]

Add test

[keith]

lld/MachO/ObjC.cpp

41

Do you need this? it seems like using section_names::swift in the startswith below works as well?

[tt]

lld/MachO/ObjC.cpp

41

Whoops, yes don't need this. Autocomplete didn't suggest me startswith with a cstring. I guess autocomplete doesn't suggest me functions when there are implicit conversations.

[tt]

Simplify

[thevinster]

LGTM

[tt]

Remove empty line

lld/MachO/ObjC.cpp

 //===- ObjC.cpp -----------------------------------------------------------===//
 //
 // 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
 //
 //===----------------------------------------------------------------------===//
 
if (const auto *c =
           findCommand<typename LP::segment_command>(hdr, LP::segmentLCType)) {
     auto sectionHeaders = ArrayRef<SectionHeader>{
         reinterpret_cast<const SectionHeader *>(c + 1), c->nsects};
     for (const SectionHeader &secHead : sectionHeaders) {
       StringRef sectname(secHead.sectname,
                          strnlen(secHead.sectname, sizeof(secHead.sectname)));
       StringRef segname(secHead.segname,
                         strnlen(secHead.segname, sizeof(secHead.segname)));
+
       if ((segname == segment_names::data &&
            sectname == section_names::objcCatList) ||
           (segname == segment_names::text &&
-           sectname == section_names::swift)) {
+           sectname.startswith(section_names::swift))) {
         return true;
       }
     }
   }
   return false;
 }
 
 static bool objectHasObjCSection(MemoryBufferRef mb) {

lld/test/MachO/objc.s

 # REQUIRES: x86, arm
 # RUN: rm -rf %t; split-file %s %t
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-objc-symbol.s -o %t/has-objc-symbol.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-objc-category.s -o %t/has-objc-category.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-objc-symbol-and-category.s -o %t/has-objc-symbol-and-category.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-swift.s -o %t/has-swift.o
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/has-swift-proto.s -o %t/has-swift-proto.o
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/no-objc.s -o %t/no-objc.o
 ## Make sure we don't mis-parse a 32-bit file as 64-bit
 # RUN: llvm-mc -filetype=obj -triple=armv7-apple-watchos %t/no-objc.s -o %t/wrong-arch.o
-# RUN: llvm-ar rcs %t/libHasSomeObjC.a %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/wrong-arch.o
-# RUN: llvm-ar rcs %t/libHasSomeObjC2.a %t/no-objc.o %t/has-objc-symbol-and-category.o %t/has-swift.o %t/wrong-arch.o
+# RUN: llvm-ar rcs %t/libHasSomeObjC.a %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/has-swift-proto.o %t/wrong-arch.o
+# RUN: llvm-ar rcs %t/libHasSomeObjC2.a %t/no-objc.o %t/has-objc-symbol-and-category.o %t/has-swift.o %t/has-swift-proto.o %t/wrong-arch.o
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
 
 # RUN: %lld -lSystem %t/test.o -o %t/test -L%t -lHasSomeObjC -ObjC
 # RUN: llvm-objdump --section-headers --syms %t/test | FileCheck %s --check-prefix=OBJC
 
 # RUN: %lld -lSystem %t/test.o -o %t/test -L%t -lHasSomeObjC2 -ObjC
 # RUN: llvm-objdump --section-headers --syms %t/test | FileCheck %s --check-prefix=OBJC
 
-# RUN: %lld -lSystem %t/test.o -o %t/test --start-lib %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/wrong-arch.o --end-lib -ObjC
+# RUN: %lld -lSystem %t/test.o -o %t/test --start-lib %t/no-objc.o %t/has-objc-symbol.o %t/has-objc-category.o %t/has-swift.o %t/has-swift-proto.o %t/wrong-arch.o --end-lib -ObjC
 # RUN: llvm-objdump --section-headers --syms %t/test | FileCheck %s --check-prefix=OBJC
 
 # OBJC:       Sections:
 # OBJC-NEXT:  Idx Name            Size   VMA  Type
 # OBJC-NEXT:    0 __text          {{.*}}      TEXT
 # OBJC-NEXT:    1 __swift         {{.*}}      DATA
-# OBJC-NEXT:    2 __objc_catlist  {{.*}}      DATA
-# OBJC-NEXT:    3 has_objc_symbol {{.*}}      DATA
+# OBJC-NEXT:    2 __swift5_fieldmd{{.*}}      DATA
+# OBJC-NEXT:    3 __objc_catlist  {{.*}}      DATA
+# OBJC-NEXT:    4 has_objc_symbol {{.*}}      DATA
 # OBJC-EMPTY:
 # OBJC-NEXT:  SYMBOL TABLE:
 # OBJC-DAG:   g     F __TEXT,__text _main
 # OBJC-DAG:   g     F __TEXT,__text _OBJC_CLASS_$_MyObject
+# OBJC-DAG:   g     O __TEXT,__swift5_fieldmd $s7somelib4Blah_pMF
 
 # RUN: %lld -lSystem %t/test.o -o %t/test -L%t -lHasSomeObjC
 # RUN: llvm-objdump --section-headers --syms %t/test | FileCheck %s --check-prefix=NO-OBJC
 
 # NO-OBJC:       Sections:
 # NO-OBJC-NEXT:  Idx Name           Size   VMA  Type
 # NO-OBJC-NEXT:    0 __text         {{.*}}      TEXT
 # NO-OBJC-EMPTY:

 
 .section __DATA,__objc_catlist
 .quad 0x1234
 
 #--- has-swift.s
 .section __TEXT,__swift
 .quad 0x1234
 
+#--- has-swift-proto.s
+.section __TEXT,__swift5_fieldmd
+.globl $s7somelib4Blah_pMF
+$s7somelib4Blah_pMF:
+
 #--- no-objc.s
 ## This archive member should not be pulled in by -ObjC since it does not
 ## contain any ObjC-related data.
 .globl _has_dup
 .section __DATA,foo
 .section __DATA,bar
 .section __DATA,no_objc
 _has_dup: