[BOLT] Implement createRelocation for AArch64

The implementation is based on the X86 version, with the same code
of symbol and addend extraction. The differences include the
support for RelType `R_AARCH64_CALL26` and the deletion of 8-bit
relocation.

Reviewed By: rafauler

Differential Revision: https://reviews.llvm.org/D156018

Author: Kepontry

bolt/lib/Core/Relocation.cpp

@@ -345,6 +345,13 @@ static uint64_t encodeValueAArch64(uint64_t Type, uint64_t Value, uint64_t PC) {
   case ELF::R_AARCH64_PREL64:
     Value -= PC;
     break;
+  case ELF::R_AARCH64_CALL26:
+    Value -= PC;
+    assert(isInt<28>(Value) && "only PC +/- 128MB is allowed for direct call");
+    // Immediate goes in bits 25:0 of BL.
+    // OP 1001_01 goes in bits 31:26 of BL.
+    Value = (Value >> 2) | 0x94000000ULL;
+    break;
   }
   return Value;
 }

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -11,11 +11,13 @@
 //===----------------------------------------------------------------------===//
 
 #include "MCTargetDesc/AArch64AddressingModes.h"
+#include "MCTargetDesc/AArch64FixupKinds.h"
 #include "MCTargetDesc/AArch64MCExpr.h"
 #include "MCTargetDesc/AArch64MCTargetDesc.h"
 #include "Utils/AArch64BaseInfo.h"
 #include "bolt/Core/MCPlusBuilder.h"
 #include "llvm/BinaryFormat/ELF.h"
+#include "llvm/MC/MCFixupKindInfo.h"
 #include "llvm/MC/MCInstrInfo.h"
 #include "llvm/MC/MCRegisterInfo.h"
 #include "llvm/Support/Debug.h"
@@ -1160,6 +1162,52 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
                           ELF::R_AARCH64_ADD_ABS_LO12_NC);
     return Insts;
   }
+
+  std::optional<Relocation>
+  createRelocation(const MCFixup &Fixup,
+                   const MCAsmBackend &MAB) const override {
+    const MCFixupKindInfo &FKI = MAB.getFixupKindInfo(Fixup.getKind());
+
+    assert(FKI.TargetOffset == 0 && "0-bit relocation offset expected");
+    const uint64_t RelOffset = Fixup.getOffset();
+
+    uint64_t RelType;
+    if (Fixup.getKind() == MCFixupKind(AArch64::fixup_aarch64_pcrel_call26))
+      RelType = ELF::R_AARCH64_CALL26;
+    else if (FKI.Flags & MCFixupKindInfo::FKF_IsPCRel) {
+      switch (FKI.TargetSize) {
+      default:
+        return std::nullopt;
+      case 16:
+        RelType = ELF::R_AARCH64_PREL16;
+        break;
+      case 32:
+        RelType = ELF::R_AARCH64_PREL32;
+        break;
+      case 64:
+        RelType = ELF::R_AARCH64_PREL64;
+        break;
+      }
+    } else {
+      switch (FKI.TargetSize) {
+      default:
+        return std::nullopt;
+      case 16:
+        RelType = ELF::R_AARCH64_ABS16;
+        break;
+      case 32:
+        RelType = ELF::R_AARCH64_ABS32;
+        break;
+      case 64:
+        RelType = ELF::R_AARCH64_ABS64;
+        break;
+      }
+    }
+
+    auto [RelSymbol, RelAddend] = extractFixupExpr(Fixup);
+
+    return Relocation({RelOffset, RelSymbol, RelType, RelAddend, 0});
+  }
 };
 
 } // end anonymous namespace

bolt/test/AArch64/reloc-call26.s

@@ -0,0 +1,29 @@
+## This test checks processing of R_AARCH64_CALL26 relocation
+## when option `--funcs` is enabled
+
+# REQUIRES: system-linux
+
+# RUN: llvm-mc -filetype=obj -triple aarch64-unknown-unknown \
+# RUN:   %s -o %t.o
+# RUN: %clang %cflags %t.o -o %t.exe -Wl,-q
+# RUN: llvm-bolt %t.exe -o %t.bolt --funcs=func1
+# RUN: llvm-objdump -d --disassemble-symbols='_start' %t.bolt | \
+# RUN:   FileCheck %s
+
+# CHECK: {{.*}} bl {{.*}} <func1>
+
+  .text
+  .align 4
+  .global _start
+  .type _start, %function
+_start:
+  bl func1
+  mov     w8, #93
+  svc     #0
+  .size _start, .-_start
+
+  .global func1
+  .type func1, %function
+func1:
+  ret
+  .size func1, .-func1