[lld-macho] Ensure that chained fixups data comes first in __LINKEDIT

libstuff-based tools (e.g. `codesign` and `strip`) require
`__chainfixups` to be the first section in `__LINKEDIT`, and print a
"file not in an order that can be processed" error message if that is
not the case.

Differential Revision: https://reviews.llvm.org/D137492

lld/MachO/OutputSegment.cpp

@@ -125,6 +125,7 @@ static int sectionOrder(OutputSection *osec) {
     }
   } else if (segname == segment_names::linkEdit) {
     return StringSwitch<int>(osec->name)
+        .Case(section_names::chainFixups, -11)
         .Case(section_names::rebase, -10)
         .Case(section_names::binding, -9)
         .Case(section_names::weakBinding, -8)

lld/test/MachO/linkedit-contiguity.s

@@ -2,36 +2,49 @@
 # RUN: rm -rf %t; split-file %s %t
 
 ## codesign requires that each section in __LINKEDIT ends where the next one
-## starts. This test enforces that invariant.
+## starts and that they follow a certain order. This test enforces that invariant.
 ## It also checks that the last section in __LINKEDIT covers the last byte of
 ## the segment.
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/foo.s -o %t/foo.o
 # RUN: %lld %t/foo.o -dylib -o %t/libfoo.dylib
 
 # RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %t/test.s -o %t/test.o
+
 # RUN: %lld -lSystem -adhoc_codesign -o %t/test %t/libfoo.dylib %t/test.o
+# RUN: llvm-objdump --macho --all-headers %t/test | FileCheck --check-prefixes=CHECK,OPCODE %s
 
-# RUN: llvm-objdump --macho --all-headers %t/test | FileCheck %s
+# RUN: %lld -lSystem -adhoc_codesign -fixup_chains -o %t/chained_test %t/libfoo.dylib %t/test.o
+# RUN: llvm-objdump --macho --all-headers %t/chained_test | FileCheck --check-prefixes=CHECK,CHAINED %s
 
 # CHECK:      segname __LINKEDIT
 # CHECK-NEXT: vmaddr
 # CHECK-NEXT: vmsize
 # CHECK-NEXT: fileoff [[#LINKEDIT_OFF:]]
 # CHECK-NEXT: filesize [[#LINKEDIT_SIZE:]]
 
-# CHECK:      cmd LC_DYLD_INFO_ONLY
-# CHECK-NEXT: cmdsize 48
-# CHECK-NEXT: rebase_off [[#REBASE_OFF:]]
-# CHECK-NEXT: rebase_size [[#REBASE_SIZE:]]
-# CHECK-NEXT: bind_off [[#BIND_OFF: REBASE_OFF + REBASE_SIZE]]
-# CHECK-NEXT: bind_size [[#BIND_SIZE:]]
-# CHECK-NEXT: weak_bind_off [[#WEAK_OFF: BIND_OFF + BIND_SIZE]]
-# CHECK-NEXT: weak_bind_size [[#WEAK_SIZE:]]
-# CHECK-NEXT: lazy_bind_off [[#LAZY_OFF: WEAK_OFF + WEAK_SIZE]]
-# CHECK-NEXT: lazy_bind_size [[#LAZY_SIZE:]]
-# CHECK-NEXT: export_off [[#EXPORT_OFF: LAZY_OFF + LAZY_SIZE]]
-# CHECK-NEXT: export_size [[#EXPORT_SIZE:]]
+# OPCODE:      cmd LC_DYLD_INFO_ONLY
+# OPCODE-NEXT: cmdsize 48
+# OPCODE-NEXT: rebase_off [[#REBASE_OFF:]]
+# OPCODE-NEXT: rebase_size [[#REBASE_SIZE:]]
+# OPCODE-NEXT: bind_off [[#BIND_OFF: REBASE_OFF + REBASE_SIZE]]
+# OPCODE-NEXT: bind_size [[#BIND_SIZE:]]
+# OPCODE-NEXT: weak_bind_off [[#WEAK_OFF: BIND_OFF + BIND_SIZE]]
+# OPCODE-NEXT: weak_bind_size [[#WEAK_SIZE:]]
+# OPCODE-NEXT: lazy_bind_off [[#LAZY_OFF: WEAK_OFF + WEAK_SIZE]]
+# OPCODE-NEXT: lazy_bind_size [[#LAZY_SIZE:]]
+# OPCODE-NEXT: export_off [[#EXPORT_OFF: LAZY_OFF + LAZY_SIZE]]
+# OPCODE-NEXT: export_size [[#EXPORT_SIZE:]]
+
+# CHAINED:      cmd LC_DYLD_CHAINED_FIXUPS
+# CHAINED-NEXT: cmdsize
+# CHAINED-NEXT: dataoff [[#FIXUPS_OFF: LINKEDIT_OFF]]
+# CHAINED-NEXT: datasize [[#FIXUPS_SIZE:]]
+
+# CHAINED:      cmd LC_DYLD_EXPORTS_TRIE
+# CHAINED-NEXT: cmdsize
+# CHAINED-NEXT: dataoff [[#EXPORT_OFF: FIXUPS_OFF + FIXUPS_SIZE]]
+# CHAINED-NEXT: datasize [[#EXPORT_SIZE:]]
 
 # CHECK:      cmd LC_FUNCTION_STARTS
 # CHECK-NEXT: cmdsize