[PAC][CodeGen][ELF][AArch64] Support signed GOT (#96164)

Depends on #96158 and #96159

Support the following relocations and assembly operators:

- `R_AARCH64_AUTH_ADR_GOT_PAGE` (`:got_auth:` for `adrp`)
- `R_AARCH64_AUTH_LD64_GOT_LO12_NC` (`:got_auth_lo12:` for `ldr`)
- `R_AARCH64_AUTH_GOT_ADD_LO12_NC` (`:got_auth_lo12:` for `add`)

`LOADgotAUTH` pseudo-instruction is introduced which is later expanded
to actual instruction sequence like the following.

```
adrp x16, :got_auth:sym
add x16, x16, :got_auth_lo12:sym
ldr x0, [x16]
autia x0, x16
```

If a resign is requested, like below, `LOADgotPAC` pseudo is used, and
GOT load is lowered similarly to `LOADgotAUTH`.

```
@var = global i32 0
define ptr @resign_globalvar() {
  ret ptr ptrauth (ptr @var, i32 3, i64 43)
}
```

Both SelectionDAG and GlobalISel are suppported. For FastISel, we fall
back to SelectionDAG.

Tests starting with 'ptrauth-' have corresponding variants w/o this
prefix.

See also specification
https://github.com/ARM-software/abi-aa/blob/main/pauthabielf64/pauthabielf64.rst#appendix-signed-got

Author: kovdan01

llvm/lib/Target/AArch64/AArch64AsmPrinter.cpp

@@ -2161,6 +2161,10 @@ void AArch64AsmPrinter::LowerMOVaddrPAC(const MachineInstr &MI) {
   };
 
   const bool IsGOTLoad = MI.getOpcode() == AArch64::LOADgotPAC;
+  const bool IsELFSignedGOT = MI.getParent()
+                                  ->getParent()
+                                  ->getInfo<AArch64FunctionInfo>()
+                                  ->hasELFSignedGOT();
   MachineOperand GAOp = MI.getOperand(0);
   const uint64_t KeyC = MI.getOperand(1).getImm();
   assert(KeyC <= AArch64PACKey::LAST &&
@@ -2177,9 +2181,16 @@ void AArch64AsmPrinter::LowerMOVaddrPAC(const MachineInstr &MI) {
   // Emit:
   // target materialization:
   // - via GOT:
-  //     adrp x16, :got:target
-  //     ldr x16, [x16, :got_lo12:target]
-  //     add offset to x16 if offset != 0
+  //   - unsigned GOT:
+  //       adrp x16, :got:target
+  //       ldr x16, [x16, :got_lo12:target]
+  //       add offset to x16 if offset != 0
+  //   - ELF signed GOT:
+  //       adrp x17, :got:target
+  //       add x17, x17, :got_auth_lo12:target
+  //       ldr x16, [x17]
+  //       aut{i|d}a x16, x17
+  //       add offset to x16 if offset != 0
   //
   // - direct:
   //     adrp x16, target
@@ -2222,13 +2233,40 @@ void AArch64AsmPrinter::LowerMOVaddrPAC(const MachineInstr &MI) {
   MCInstLowering.lowerOperand(GAMOLo, GAMCLo);
 
   EmitAndIncrement(
-      MCInstBuilder(AArch64::ADRP).addReg(AArch64::X16).addOperand(GAMCHi));
+      MCInstBuilder(AArch64::ADRP)
+          .addReg(IsGOTLoad && IsELFSignedGOT ? AArch64::X17 : AArch64::X16)
+          .addOperand(GAMCHi));
 
   if (IsGOTLoad) {
-    EmitAndIncrement(MCInstBuilder(AArch64::LDRXui)
-                         .addReg(AArch64::X16)
-                         .addReg(AArch64::X16)
-                         .addOperand(GAMCLo));
+    if (IsELFSignedGOT) {
+      EmitAndIncrement(MCInstBuilder(AArch64::ADDXri)
+                           .addReg(AArch64::X17)
+                           .addReg(AArch64::X17)
+                           .addOperand(GAMCLo)
+                           .addImm(0));
+
+      EmitAndIncrement(MCInstBuilder(AArch64::LDRXui)
+                           .addReg(AArch64::X16)
+                           .addReg(AArch64::X17)
+                           .addImm(0));
+
+      assert(GAOp.isGlobal());
+      assert(GAOp.getGlobal()->getValueType() != nullptr);
+      unsigned AuthOpcode = GAOp.getGlobal()->getValueType()->isFunctionTy()
+                                ? AArch64::AUTIA
+                                : AArch64::AUTDA;
+
+      EmitAndIncrement(MCInstBuilder(AuthOpcode)
+                           .addReg(AArch64::X16)
+                           .addReg(AArch64::X16)
+                           .addReg(AArch64::X17));
+
+    } else {
+      EmitAndIncrement(MCInstBuilder(AArch64::LDRXui)
+                           .addReg(AArch64::X16)
+                           .addReg(AArch64::X16)
+                           .addOperand(GAMCLo));
+    }
   } else {
     EmitAndIncrement(MCInstBuilder(AArch64::ADDXri)
                          .addReg(AArch64::X16)

llvm/lib/Target/AArch64/AArch64ExpandPseudoInsts.cpp

@@ -1291,7 +1291,40 @@ bool AArch64ExpandPseudo::expandMI(MachineBasicBlock &MBB,
     MI.eraseFromParent();
     return true;
   }
+  case AArch64::LOADgotAUTH: {
+    Register DstReg = MI.getOperand(0).getReg();
+    const MachineOperand &MO1 = MI.getOperand(1);
+
+    MachineOperand GAHiOp(MO1);
+    MachineOperand GALoOp(MO1);
+    GAHiOp.addTargetFlag(AArch64II::MO_PAGE);
+    GALoOp.addTargetFlag(AArch64II::MO_PAGEOFF | AArch64II::MO_NC);
+
+    DebugLoc DL = MI.getDebugLoc();
+    BuildMI(MBB, MBBI, MI.getDebugLoc(), TII->get(AArch64::ADRP), AArch64::X16)
+        .add(GAHiOp);
 
+    BuildMI(MBB, MBBI, DL, TII->get(AArch64::ADDXri), AArch64::X16)
+        .addReg(AArch64::X16)
+        .add(GALoOp)
+        .addImm(0);
+
+    BuildMI(MBB, MBBI, DL, TII->get(AArch64::LDRXui), DstReg)
+        .addReg(AArch64::X16)
+        .addImm(0);
+
+    assert(MO1.isGlobal());
+    assert(MO1.getGlobal()->getValueType() != nullptr);
+    unsigned AuthOpcode = MO1.getGlobal()->getValueType()->isFunctionTy()
+                              ? AArch64::AUTIA
+                              : AArch64::AUTDA;
+    BuildMI(MBB, MBBI, DL, TII->get(AuthOpcode), DstReg)
+        .addReg(DstReg)
+        .addReg(AArch64::X16);
+
+    MI.eraseFromParent();
+    return true;
+  }
   case AArch64::LOADgot: {
     MachineFunction *MF = MBB.getParent();
     Register DstReg = MI.getOperand(0).getReg();

llvm/lib/Target/AArch64/AArch64FastISel.cpp

@@ -453,6 +453,9 @@ unsigned AArch64FastISel::materializeGV(const GlobalValue *GV) {
   if (!Subtarget->useSmallAddressing() && !Subtarget->isTargetMachO())
     return 0;
 
+  if (FuncInfo.MF->getInfo<AArch64FunctionInfo>()->hasELFSignedGOT())
+    return 0;
+
   unsigned OpFlags = Subtarget->ClassifyGlobalReference(GV, TM);
 
   EVT DestEVT = TLI.getValueType(DL, GV->getType(), true);

llvm/lib/Target/AArch64/AArch64ISelLowering.cpp

@@ -9225,6 +9225,11 @@ SDValue AArch64TargetLowering::getGOT(NodeTy *N, SelectionDAG &DAG,
   SDValue GotAddr = getTargetNode(N, Ty, DAG, AArch64II::MO_GOT | Flags);
   // FIXME: Once remat is capable of dealing with instructions with register
   // operands, expand this into two nodes instead of using a wrapper node.
+  if (DAG.getMachineFunction()
+          .getInfo<AArch64FunctionInfo>()
+          ->hasELFSignedGOT())
+    return SDValue(DAG.getMachineNode(AArch64::LOADgotAUTH, DL, Ty, GotAddr),
+                   0);
   return DAG.getNode(AArch64ISD::LOADgot, DL, Ty, GotAddr);
 }
 

llvm/lib/Target/AArch64/AArch64InstrInfo.td

@@ -1872,7 +1872,7 @@ let Predicates = [HasPAuth] in {
                Sched<[WriteI, ReadI]> {
     let isReMaterializable = 1;
     let isCodeGenOnly = 1;
-    let Size = 40; // 12 fixed + 28 variable, for pointer offset, and discriminator
+    let Size = 48; // 12 fixed + 36 variable, for pointer offset, and discriminator
     let Defs = [X16,X17];
   }
 
@@ -1911,6 +1911,11 @@ let Predicates = [HasPAuth] in {
                                 tcGPR64:$AddrDisc),
               (AUTH_TCRETURN_BTI tcGPRx16x17:$dst, imm:$FPDiff, imm:$Key,
                                  imm:$Disc, tcGPR64:$AddrDisc)>;
+
+  def LOADgotAUTH : Pseudo<(outs GPR64common:$dst), (ins i64imm:$addr), []>,
+               Sched<[WriteI, ReadI]> {
+    let Defs = [X16];
+  }
 }
 
 // v9.5-A pointer authentication extensions

llvm/lib/Target/AArch64/AArch64MCInstLower.cpp

@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "AArch64MCInstLower.h"
+#include "AArch64MachineFunctionInfo.h"
 #include "MCTargetDesc/AArch64MCExpr.h"
 #include "Utils/AArch64BaseInfo.h"
 #include "llvm/CodeGen/AsmPrinter.h"
@@ -185,9 +186,12 @@ MCOperand AArch64MCInstLower::lowerSymbolOperandELF(const MachineOperand &MO,
                                                     MCSymbol *Sym) const {
   uint32_t RefFlags = 0;
 
-  if (MO.getTargetFlags() & AArch64II::MO_GOT)
-    RefFlags |= AArch64MCExpr::VK_GOT;
-  else if (MO.getTargetFlags() & AArch64II::MO_TLS) {
+  if (MO.getTargetFlags() & AArch64II::MO_GOT) {
+    const MachineFunction *MF = MO.getParent()->getParent()->getParent();
+    RefFlags |= (MF->getInfo<AArch64FunctionInfo>()->hasELFSignedGOT()
+                     ? AArch64MCExpr::VK_GOT_AUTH
+                     : AArch64MCExpr::VK_GOT);
+  } else if (MO.getTargetFlags() & AArch64II::MO_TLS) {
     TLSModel::Model Model;
     if (MO.isGlobal()) {
       const GlobalValue *GV = MO.getGlobal();

llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.cpp

@@ -16,6 +16,7 @@
 #include "AArch64MachineFunctionInfo.h"
 #include "AArch64InstrInfo.h"
 #include "AArch64Subtarget.h"
+#include "llvm/BinaryFormat/ELF.h"
 #include "llvm/IR/Constants.h"
 #include "llvm/IR/Metadata.h"
 #include "llvm/IR/Module.h"
@@ -72,6 +73,29 @@ static bool ShouldSignWithBKey(const Function &F, const AArch64Subtarget &STI) {
   return Key == "b_key";
 }
 
+// Determine if we need to treat pointers in GOT as signed (as described in
+// https://github.com/ARM-software/abi-aa/blob/main/pauthabielf64/pauthabielf64.rst#appendix-signed-got)
+// based on PAuth core info encoded as "aarch64-elf-pauthabi-platform" and
+// "aarch64-elf-pauthabi-version" module flags. Currently, only
+// AARCH64_PAUTH_PLATFORM_LLVM_LINUX platform supports signed GOT with
+// AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_GOT bit in version value set.
+static bool hasELFSignedGOTHelper(const Function &F,
+                                  const AArch64Subtarget *STI) {
+  if (!Triple(STI->getTargetTriple()).isOSBinFormatELF())
+    return false;
+  const Module *M = F.getParent();
+  const auto *PAP = mdconst::extract_or_null<ConstantInt>(
+      M->getModuleFlag("aarch64-elf-pauthabi-platform"));
+  if (!PAP || PAP->getZExtValue() != ELF::AARCH64_PAUTH_PLATFORM_LLVM_LINUX)
+    return false;
+  const auto *PAV = mdconst::extract_or_null<ConstantInt>(
+      M->getModuleFlag("aarch64-elf-pauthabi-version"));
+  if (!PAV)
+    return false;
+  return PAV->getZExtValue() &
+         (1 << ELF::AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_GOT);
+}
+
 AArch64FunctionInfo::AArch64FunctionInfo(const Function &F,
                                          const AArch64Subtarget *STI) {
   // If we already know that the function doesn't have a redzone, set
@@ -80,6 +104,7 @@ AArch64FunctionInfo::AArch64FunctionInfo(const Function &F,
     HasRedZone = false;
   std::tie(SignReturnAddress, SignReturnAddressAll) = GetSignReturnAddress(F);
   SignWithBKey = ShouldSignWithBKey(F, *STI);
+  HasELFSignedGOT = hasELFSignedGOTHelper(F, STI);
   // TODO: skip functions that have no instrumented allocas for optimization
   IsMTETagged = F.hasFnAttribute(Attribute::SanitizeMemTag);
 

llvm/lib/Target/AArch64/AArch64MachineFunctionInfo.h

@@ -177,6 +177,14 @@ class AArch64FunctionInfo final : public MachineFunctionInfo {
   /// SignWithBKey modifies the default PAC-RET mode to signing with the B key.
   bool SignWithBKey = false;
 
+  /// HasELFSignedGOT is true if the target binary format is ELF and the IR
+  /// module containing the corresponding function has the following flags:
+  /// - aarch64-elf-pauthabi-platform flag equal to
+  ///   AARCH64_PAUTH_PLATFORM_LLVM_LINUX;
+  /// - aarch64-elf-pauthabi-version flag with
+  ///   AARCH64_PAUTH_PLATFORM_LLVM_LINUX_VERSION_GOT bit set.
+  bool HasELFSignedGOT = false;
+
   /// SigningInstrOffset captures the offset of the PAC-RET signing instruction
   /// within the prologue, so it can be re-used for authentication in the
   /// epilogue when using PC as a second salt (FEAT_PAuth_LR)
@@ -509,6 +517,8 @@ class AArch64FunctionInfo final : public MachineFunctionInfo {
 
   bool shouldSignWithBKey() const { return SignWithBKey; }
 
+  bool hasELFSignedGOT() const { return HasELFSignedGOT; }
+
   MCSymbol *getSigningInstrLabel() const { return SignInstrLabel; }
   void setSigningInstrLabel(MCSymbol *Label) { SignInstrLabel = Label; }
 

llvm/lib/Target/AArch64/AsmParser/AArch64AsmParser.cpp

@@ -875,6 +875,7 @@ class AArch64Operand : public MCParsedAsmOperand {
     if (DarwinRefKind == MCSymbolRefExpr::VK_PAGEOFF ||
         ELFRefKind == AArch64MCExpr::VK_LO12 ||
         ELFRefKind == AArch64MCExpr::VK_GOT_LO12 ||
+        ELFRefKind == AArch64MCExpr::VK_GOT_AUTH_LO12 ||
         ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12 ||
         ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12_NC ||
         ELFRefKind == AArch64MCExpr::VK_TPREL_LO12 ||
@@ -986,19 +987,20 @@ class AArch64Operand : public MCParsedAsmOperand {
     int64_t Addend;
     if (AArch64AsmParser::classifySymbolRef(Expr, ELFRefKind,
                                           DarwinRefKind, Addend)) {
-      return DarwinRefKind == MCSymbolRefExpr::VK_PAGEOFF
-          || DarwinRefKind == MCSymbolRefExpr::VK_TLVPPAGEOFF
-          || (DarwinRefKind == MCSymbolRefExpr::VK_GOTPAGEOFF && Addend == 0)
-          || ELFRefKind == AArch64MCExpr::VK_LO12
-          || ELFRefKind == AArch64MCExpr::VK_DTPREL_HI12
-          || ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12
-          || ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12_NC
-          || ELFRefKind == AArch64MCExpr::VK_TPREL_HI12
-          || ELFRefKind == AArch64MCExpr::VK_TPREL_LO12
-          || ELFRefKind == AArch64MCExpr::VK_TPREL_LO12_NC
-          || ELFRefKind == AArch64MCExpr::VK_TLSDESC_LO12
-          || ELFRefKind == AArch64MCExpr::VK_SECREL_HI12
-          || ELFRefKind == AArch64MCExpr::VK_SECREL_LO12;
+      return DarwinRefKind == MCSymbolRefExpr::VK_PAGEOFF ||
+             DarwinRefKind == MCSymbolRefExpr::VK_TLVPPAGEOFF ||
+             (DarwinRefKind == MCSymbolRefExpr::VK_GOTPAGEOFF && Addend == 0) ||
+             ELFRefKind == AArch64MCExpr::VK_LO12 ||
+             ELFRefKind == AArch64MCExpr::VK_GOT_AUTH_LO12 ||
+             ELFRefKind == AArch64MCExpr::VK_DTPREL_HI12 ||
+             ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12 ||
+             ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12_NC ||
+             ELFRefKind == AArch64MCExpr::VK_TPREL_HI12 ||
+             ELFRefKind == AArch64MCExpr::VK_TPREL_LO12 ||
+             ELFRefKind == AArch64MCExpr::VK_TPREL_LO12_NC ||
+             ELFRefKind == AArch64MCExpr::VK_TLSDESC_LO12 ||
+             ELFRefKind == AArch64MCExpr::VK_SECREL_HI12 ||
+             ELFRefKind == AArch64MCExpr::VK_SECREL_LO12;
     }
 
     // If it's a constant, it should be a real immediate in range.
@@ -3250,6 +3252,7 @@ ParseStatus AArch64AsmParser::tryParseAdrpLabel(OperandVector &Operands) {
                DarwinRefKind != MCSymbolRefExpr::VK_TLVPPAGE &&
                ELFRefKind != AArch64MCExpr::VK_ABS_PAGE_NC &&
                ELFRefKind != AArch64MCExpr::VK_GOT_PAGE &&
+               ELFRefKind != AArch64MCExpr::VK_GOT_AUTH_PAGE &&
                ELFRefKind != AArch64MCExpr::VK_GOT_PAGE_LO15 &&
                ELFRefKind != AArch64MCExpr::VK_GOTTPREL_PAGE &&
                ELFRefKind != AArch64MCExpr::VK_TLSDESC_PAGE) {
@@ -4334,6 +4337,8 @@ bool AArch64AsmParser::parseSymbolicImmVal(const MCExpr *&ImmVal) {
                   .Case("got", AArch64MCExpr::VK_GOT_PAGE)
                   .Case("gotpage_lo15", AArch64MCExpr::VK_GOT_PAGE_LO15)
                   .Case("got_lo12", AArch64MCExpr::VK_GOT_LO12)
+                  .Case("got_auth", AArch64MCExpr::VK_GOT_AUTH_PAGE)
+                  .Case("got_auth_lo12", AArch64MCExpr::VK_GOT_AUTH_LO12)
                   .Case("gottprel", AArch64MCExpr::VK_GOTTPREL_PAGE)
                   .Case("gottprel_lo12", AArch64MCExpr::VK_GOTTPREL_LO12_NC)
                   .Case("gottprel_g1", AArch64MCExpr::VK_GOTTPREL_G1)
@@ -5708,6 +5713,7 @@ bool AArch64AsmParser::validateInstruction(MCInst &Inst, SMLoc &IDLoc,
 
         // Only allow these with ADDXri/ADDWri
         if ((ELFRefKind == AArch64MCExpr::VK_LO12 ||
+             ELFRefKind == AArch64MCExpr::VK_GOT_AUTH_LO12 ||
              ELFRefKind == AArch64MCExpr::VK_DTPREL_HI12 ||
              ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12 ||
              ELFRefKind == AArch64MCExpr::VK_DTPREL_LO12_NC ||

llvm/lib/Target/AArch64/GISel/AArch64InstructionSelector.cpp

@@ -2845,7 +2845,9 @@ bool AArch64InstructionSelector::select(MachineInstr &I) {
     }
 
     if (OpFlags & AArch64II::MO_GOT) {
-      I.setDesc(TII.get(AArch64::LOADgot));
+      I.setDesc(TII.get(MF.getInfo<AArch64FunctionInfo>()->hasELFSignedGOT()
+                            ? AArch64::LOADgotAUTH
+                            : AArch64::LOADgot));
       I.getOperand(1).setTargetFlags(OpFlags);
     } else if (TM.getCodeModel() == CodeModel::Large &&
                !TM.isPositionIndependent()) {

llvm/lib/Target/AArch64/MCTargetDesc/AArch64ELFObjectWriter.cpp

@@ -167,6 +167,15 @@ unsigned AArch64ELFObjectWriter::getRelocType(MCContext &Ctx,
       }
       if (SymLoc == AArch64MCExpr::VK_GOT && !IsNC)
         return R_CLS(ADR_GOT_PAGE);
+      if (SymLoc == AArch64MCExpr::VK_GOT_AUTH && !IsNC) {
+        if (IsILP32) {
+          Ctx.reportError(Fixup.getLoc(),
+                          "ILP32 ADRP AUTH relocation not supported "
+                          "(LP64 eqv: AUTH_ADR_GOT_PAGE)");
+          return ELF::R_AARCH64_NONE;
+        }
+        return ELF::R_AARCH64_AUTH_ADR_GOT_PAGE;
+      }
       if (SymLoc == AArch64MCExpr::VK_GOTTPREL && !IsNC)
         return R_CLS(TLSIE_ADR_GOTTPREL_PAGE21);
       if (SymLoc == AArch64MCExpr::VK_TLSDESC && !IsNC)
@@ -237,6 +246,15 @@ unsigned AArch64ELFObjectWriter::getRelocType(MCContext &Ctx,
         return R_CLS(TLSLE_ADD_TPREL_LO12);
       if (RefKind == AArch64MCExpr::VK_TLSDESC_LO12)
         return R_CLS(TLSDESC_ADD_LO12);
+      if (RefKind == AArch64MCExpr::VK_GOT_AUTH_LO12 && IsNC) {
+        if (IsILP32) {
+          Ctx.reportError(Fixup.getLoc(),
+                          "ILP32 ADD AUTH relocation not supported "
+                          "(LP64 eqv: AUTH_GOT_ADD_LO12_NC)");
+          return ELF::R_AARCH64_NONE;
+        }
+        return ELF::R_AARCH64_AUTH_GOT_ADD_LO12_NC;
+      }
       if (SymLoc == AArch64MCExpr::VK_ABS && IsNC)
         return R_CLS(ADD_ABS_LO12_NC);
 
@@ -329,17 +347,23 @@ unsigned AArch64ELFObjectWriter::getRelocType(MCContext &Ctx,
     case AArch64::fixup_aarch64_ldst_imm12_scale8:
       if (SymLoc == AArch64MCExpr::VK_ABS && IsNC)
         return R_CLS(LDST64_ABS_LO12_NC);
-      if (SymLoc == AArch64MCExpr::VK_GOT && IsNC) {
+      if ((SymLoc == AArch64MCExpr::VK_GOT ||
+           SymLoc == AArch64MCExpr::VK_GOT_AUTH) &&
+          IsNC) {
         AArch64MCExpr::VariantKind AddressLoc =
             AArch64MCExpr::getAddressFrag(RefKind);
+        bool IsAuth = (SymLoc == AArch64MCExpr::VK_GOT_AUTH);
         if (!IsILP32) {
           if (AddressLoc == AArch64MCExpr::VK_LO15)
             return ELF::R_AARCH64_LD64_GOTPAGE_LO15;
-          return ELF::R_AARCH64_LD64_GOT_LO12_NC;
+          return (IsAuth ? ELF::R_AARCH64_AUTH_LD64_GOT_LO12_NC
+                         : ELF::R_AARCH64_LD64_GOT_LO12_NC);
         }
-        Ctx.reportError(Fixup.getLoc(), "ILP32 64-bit load/store "
-                                        "relocation not supported (LP64 eqv: "
-                                        "LD64_GOT_LO12_NC)");
+        Ctx.reportError(Fixup.getLoc(),
+                        Twine("ILP32 64-bit load/store "
+                              "relocation not supported (LP64 eqv: ") +
+                            (IsAuth ? "AUTH_GOT_LO12_NC" : "LD64_GOT_LO12_NC") +
+                            Twine(')'));
         return ELF::R_AARCH64_NONE;
       }
       if (SymLoc == AArch64MCExpr::VK_DTPREL && !IsNC)