[ELF/AARCH64] - Implemented R_AARCH64_CONDBR19 relocation.

R_AARCH64_CONDBR19 is calculated as S+A-P,
Set the immediate field of a conditional branch instruction to bits [20:2] of X; check -2^20 ≤ X< 2^20.

Afaik there is no document for AARCH64 instruction encoding from official for unknown reason, so 
I used gold source code and next link as a reference for implementation: http://kitoslab-eng.blogspot.ru/2012/10/armv8-aarch64-instruction-encoding.html. From which is clear that immediate field of a conditional branch instruction is 5 bits off. That is proved by output which is is equal to gold/bfd now.

Differential revision: http://reviews.llvm.org/D15809

llvm-svn: 257333

lld/ELF/Target.cpp

@@ -1223,6 +1223,7 @@ bool AArch64TargetInfo::relocNeedsPlt(uint32_t Type,
   default:
     return false;
   case R_AARCH64_CALL26:
+  case R_AARCH64_CONDBR19:
   case R_AARCH64_JUMP26:
     return canBePreempted(&S, true);
   }
@@ -1289,6 +1290,12 @@ void AArch64TargetInfo::relocateOne(uint8_t *Loc, uint8_t *BufEnd,
     or32le(Loc, (X & 0x0FFFFFFC) >> 2);
     break;
   }
+  case R_AARCH64_CONDBR19: {
+    uint64_t X = SA - P;
+    checkInt<21>(X, Type);
+    or32le(Loc, (X & 0x1FFFFC) << 3);
+    break;
+  }
   case R_AARCH64_LD64_GOT_LO12_NC:
     checkAlignment<8>(SA, Type);
     or32le(Loc, (SA & 0xFF8) << 7);

lld/test/ELF/Inputs/aarch64-condb-reloc.s

@@ -0,0 +1,17 @@
+.globl _foo
+_foo:
+ nop
+ nop
+ nop
+ nop
+
+.globl _bar
+_bar:
+ nop
+ nop
+ nop
+
+.globl _dah
+_dah:
+ nop
+ nop

lld/test/ELF/aarch64-condb-reloc.s

@@ -0,0 +1,99 @@
+# RUN: llvm-mc -filetype=obj -triple=aarch64-unknown-freebsd %p/Inputs/aarch64-condb-reloc.s -o %t1
+# RUN: llvm-mc -filetype=obj -triple=aarch64-unknown-freebsd %s -o %t2
+# RUN: ld.lld %t1 %t2 -o %t
+# RUN: llvm-objdump -d %t | FileCheck %s
+# RUN: ld.lld -shared %t1 %t2 -o %t3
+# RUN: llvm-objdump -d %t3 | FileCheck -check-prefix=DSO %s
+# RUN: llvm-readobj -s -r %t3 | FileCheck -check-prefix=DSOREL %s
+# REQUIRES: aarch64
+
+# 0x11024 - 36 = 0x11000
+# 0x11028 - 24 = 0x11010
+# 0x1102c - 16 = 0x1101c
+# CHECK:      Disassembly of section .text:
+# CHECK-NEXT: _foo:
+# CHECK-NEXT:    11000: {{.*}} nop
+# CHECK-NEXT:    11004: {{.*}} nop
+# CHECK-NEXT:    11008: {{.*}} nop
+# CHECK-NEXT:    1100c: {{.*}} nop
+# CHECK:      _bar:
+# CHECK-NEXT:    11010: {{.*}} nop
+# CHECK-NEXT:    11014: {{.*}} nop
+# CHECK-NEXT:    11018: {{.*}} nop
+# CHECK:      _dah:
+# CHECK-NEXT:    1101c: {{.*}} nop
+# CHECK-NEXT:    11020: {{.*}} nop
+# CHECK:      _start:
+# CHECK-NEXT:    11024: {{.*}} b.eq #-36
+# CHECK-NEXT:    11028: {{.*}} b.eq #-24
+# CHECK-NEXT:    1102c: {{.*}} b.eq #-16
+
+#DSOREL:      Section {
+#DSOREL:        Index:
+#DSOREL:        Name: .got.plt
+#DSOREL-NEXT:   Type: SHT_PROGBITS
+#DSOREL-NEXT:   Flags [
+#DSOREL-NEXT:     SHF_ALLOC
+#DSOREL-NEXT:     SHF_WRITE
+#DSOREL-NEXT:   ]
+#DSOREL-NEXT:   Address: 0x3000
+#DSOREL-NEXT:   Offset: 0x3000
+#DSOREL-NEXT:   Size: 48
+#DSOREL-NEXT:   Link: 0
+#DSOREL-NEXT:   Info: 0
+#DSOREL-NEXT:   AddressAlignment: 8
+#DSOREL-NEXT:   EntrySize: 0
+#DSOREL-NEXT:  }
+#DSOREL:      Relocations [
+#DSOREL-NEXT:  Section ({{.*}}) .rela.plt {
+#DSOREL-NEXT:    0x3018 R_AARCH64_JUMP_SLOT _foo
+#DSOREL-NEXT:    0x3020 R_AARCH64_JUMP_SLOT _bar
+#DSOREL-NEXT:    0x3028 R_AARCH64_JUMP_SLOT _dah
+#DSOREL-NEXT:  }
+#DSOREL-NEXT:]
+
+#DSO:      Disassembly of section .text:
+#DSO-NEXT: _foo:
+#DSO-NEXT:     1000: {{.*}} nop
+#DSO-NEXT:     1004: {{.*}} nop
+#DSO-NEXT:     1008: {{.*}} nop
+#DSO-NEXT:     100c: {{.*}} nop
+#DSO:      _bar:
+#DSO-NEXT:     1010: {{.*}} nop
+#DSO-NEXT:     1014: {{.*}} nop
+#DSO-NEXT:     1018: {{.*}} nop
+#DSO:      _dah:
+#DSO-NEXT:     101c: {{.*}} nop
+#DSO-NEXT:     1020: {{.*}} nop
+#DSO:      _start:
+#DSO-NEXT:     1024: {{.*}} b.eq #44
+#DSO-NEXT:     1028: {{.*}} b.eq #56
+#DSO-NEXT:     102c: {{.*}} b.eq #68
+#DSO-NEXT: Disassembly of section .plt:
+#DSO-NEXT: .plt:
+#DSO-NEXT:     1030: {{.*}} stp x16, x30, [sp, #-16]!
+#DSO-NEXT:     1034: {{.*}} adrp x16, #8192
+#DSO-NEXT:     1038: {{.*}} ldr x17, [x16, #16]
+#DSO-NEXT:     103c: {{.*}} add x16, x16, #16
+#DSO-NEXT:     1040: {{.*}} br x17
+#DSO-NEXT:     1044: {{.*}} nop
+#DSO-NEXT:     1048: {{.*}} nop
+#DSO-NEXT:     104c: {{.*}} nop
+#DSO-NEXT:     1050: {{.*}} adrp x16, #8192
+#DSO-NEXT:     1054: {{.*}} ldr x17, [x16, #24]
+#DSO-NEXT:     1058: {{.*}} add x16, x16, #24
+#DSO-NEXT:     105c: {{.*}} br x17
+#DSO-NEXT:     1060: {{.*}} adrp x16, #8192
+#DSO-NEXT:     1064: {{.*}} ldr x17, [x16, #32]
+#DSO-NEXT:     1068: {{.*}} add x16, x16, #32
+#DSO-NEXT:     106c: {{.*}} br x17
+#DSO-NEXT:     1070: {{.*}} adrp x16, #8192
+#DSO-NEXT:     1074: {{.*}} ldr x17, [x16, #40]
+#DSO-NEXT:     1078: {{.*}} add x16, x16, #40
+#DSO-NEXT:     107c: {{.*}} br x17
+
+.globl _start
+_start:
+ b.eq _foo
+ b.eq _bar
+ b.eq _dah