[lld-macho] Properly test subtractor relocations & fix their attributes

[int3]

Summary

llvm-mc doesn't generate any relocations for subtractions
between local symbols -- they must be global -- so the previous test
wasn't actually testing any relocation logic. I've fixed that and
extended the test to cover r_length=3 relocations as well as both x86_64
and arm64.

[smeenai]

LGTM

lld/test/MachO/reloc-subtractor.s

16

Little endian makes this so confusing :(

lld/MachO/Arch/ARM64.cpp

 // are weird -- it results in the value of the GOT slot being written, instead
 // of the address. Let's not support it unless we find a real-world use case.
 
 const TargetInfo::RelocAttrs &ARM64::getRelocAttrs(uint8_t type) const {
   static const std::array<TargetInfo::RelocAttrs, 11> relocAttrsArray{{
 #define B(x) RelocAttrBits::x
       {"UNSIGNED", B(UNSIGNED) | B(ABSOLUTE) | B(EXTERN) | B(LOCAL) |
                        B(DYSYM8) | B(BYTE4) | B(BYTE8)},
-      {"SUBTRACTOR", B(SUBTRAHEND) | B(BYTE8)},
+      {"SUBTRACTOR", B(SUBTRAHEND) | B(BYTE4) | B(BYTE8)},
       {"BRANCH26", B(PCREL) | B(EXTERN) | B(BRANCH) | B(BYTE4)},
       {"PAGE21", B(PCREL) | B(EXTERN) | B(BYTE4)},
       {"PAGEOFF12", B(ABSOLUTE) | B(EXTERN) | B(BYTE4)},
       {"GOT_LOAD_PAGE21", B(PCREL) | B(EXTERN) | B(GOT) | B(BYTE4)},
       {"GOT_LOAD_PAGEOFF12",
        B(ABSOLUTE) | B(EXTERN) | B(GOT) | B(LOAD) | B(BYTE4)},
       {"POINTER_TO_GOT", B(PCREL) | B(EXTERN) | B(GOT) | B(POINTER) | B(BYTE4)},
       {"TLVP_LOAD_PAGE21", B(PCREL) | B(EXTERN) | B(TLV) | B(BYTE4)},

lld/MachO/Arch/X86_64.cpp

const TargetInfo::RelocAttrs &X86_64::getRelocAttrs(uint8_t type) const {
   static const std::array<TargetInfo::RelocAttrs, 10> relocAttrsArray{{
 #define B(x) RelocAttrBits::x
       {"UNSIGNED", B(UNSIGNED) | B(ABSOLUTE) | B(EXTERN) | B(LOCAL) |
                        B(DYSYM8) | B(BYTE4) | B(BYTE8)},
       {"SIGNED", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
       {"BRANCH", B(PCREL) | B(EXTERN) | B(BRANCH) | B(BYTE4)},
       {"GOT_LOAD", B(PCREL) | B(EXTERN) | B(GOT) | B(LOAD) | B(BYTE4)},
       {"GOT", B(PCREL) | B(EXTERN) | B(GOT) | B(POINTER) | B(BYTE4)},
-      {"SUBTRACTOR", B(SUBTRAHEND)},
+      {"SUBTRACTOR", B(SUBTRAHEND) | B(BYTE4) | B(BYTE8)},
       {"SIGNED_1", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
       {"SIGNED_2", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
       {"SIGNED_4", B(PCREL) | B(EXTERN) | B(LOCAL) | B(BYTE4)},
       {"TLV", B(PCREL) | B(EXTERN) | B(TLV) | B(LOAD) | B(BYTE4)},
 #undef B
   }};
   assert(type < relocAttrsArray.size() && "invalid relocation type");
   if (type >= relocAttrsArray.size())

lld/test/MachO/reloc-subtractor.s

+# REQUIRES: x86, aarch64
+# RUN: rm -rf %t; mkdir %t
+# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t/x86_64.o
+# RUN: llvm-mc -filetype=obj -triple=arm64-apple-darwin %s -o %t/arm64.o
+# RUN: %lld -lSystem %t/x86_64.o -o %t/x86_64
+# RUN: llvm-objdump --syms --full-contents %t/x86_64 | FileCheck %s
+# RUN: %lld -arch arm64 -lSystem %t/arm64.o -o %t/arm64
+# RUN: llvm-objdump --syms --full-contents %t/arm64 | FileCheck %s
+
+# CHECK-LABEL: SYMBOL TABLE:
+# CHECK:       {{0*}}[[#%x, SUB1ADDR:]] l {{.*}} __DATA,__data _sub1
+# CHECK:       {{0*}}[[#%x, SUB2ADDR:]] l {{.*}} __DATA,__data _sub2
+# CHECK:       {{0*}}[[#%x, SUB3ADDR:]] l {{.*}} __DATA,__data _sub3
+# CHECK:       {{0*}}[[#%x, SUB4ADDR:]] l {{.*}} __DATA,__data _sub4
+# CHECK-LABEL: Contents of section __DATA,__data:
+# CHECK:       [[#SUB1ADDR]] 10000000
+# CHECK-NEXT:  [[#SUB2ADDR]] f0ffffff
+# CHECK-NEXT:  [[#SUB3ADDR]] 10000000 00000000
+# CHECK-NEXT:  [[#SUB4ADDR]] f0ffffff ffffffff
+
+.globl _main, _subtrahend_1, _subtrahend_2, _minued1, _minued2
+
+.data
+_subtrahend_1:
+  .space 16
+_minuend_1:
+  .space 16
+_minuend_2:
+  .space 16
+_subtrahend_2:
+  .space 16
+_sub1:
+  .long _minuend_1 - _subtrahend_1
+  .space 12
+_sub2:
+  .long _minuend_2 - _subtrahend_2
+  .space 12
+_sub3:
+  .quad _minuend_1 - _subtrahend_1
+  .space 8
+_sub4:
+  .quad _minuend_2 - _subtrahend_2
+
+.text
+.p2align 2
+_main:
+  ret

lld/test/MachO/x86-64-reloc-subtract.s

-# REQUIRES: x86
-# RUN: llvm-mc -filetype=obj -triple=x86_64-apple-darwin %s -o %t.o
-# RUN: %lld -o %t %t.o
-# RUN: llvm-objdump --syms --full-contents %t | FileCheck %s
-
-# CHECK-LABEL: SYMBOL TABLE:
-# CHECK: {{0*}}[[#%x, SUB1ADDR:]] g {{.*}} __DATA,subby _sub1
-# CHECK: {{0*}}[[#%x, SUB2ADDR:]] g {{.*}} __DATA,subby _sub2
-# CHECK-LABEL: Contents of section __DATA,subby:
-# CHECK: [[#SUB1ADDR]] 10000000
-# CHECK: [[#SUB2ADDR]] f0ffffff
-
-.globl _main, _sub1, _sub2
-
-.section __DATA,subby
-L_.subtrahend_1:
-  .space 16
-L_.minuend_1:
-  .space 16
-L_.minuend_2:
-  .space 16
-L_.subtrahend_2:
-  .space 16
-_sub1:
-  .long L_.minuend_1 - L_.subtrahend_1
-  .space 12
-_sub2:
-  .long L_.minuend_2 - L_.subtrahend_2
-
-.text
-_main:
-  mov $0, %rax
-  ret