From da852b03b009141b1deda8c4bda83149d64e7666 Mon Sep 17 00:00:00 2001
From: Victor Campos <victor.campos@arm.com>
Date: Wed, 24 Jun 2020 14:25:29 +0100
Subject: [PATCH] [AArch64] Emit warning when disassembling unpredictable LDRAA
 and LDRAB

Summary:
LDRAA and LDRAB in their writeback variant should softfail when the same
register is used as result and base.

This patch adds a custom decoder that catches such case and emits a
warning when it occurs.

Differential Revision: https://reviews.llvm.org/D82541
---
 llvm/lib/Target/AArch64/AArch64InstrFormats.td     |  2 ++
 .../AArch64/Disassembler/AArch64Disassembler.cpp   | 36 ++++++++++++++++++++++
 .../AArch64/armv8.3a-signed-pointer.txt            | 11 ++++++-
 3 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Target/AArch64/AArch64InstrFormats.td b/llvm/lib/Target/AArch64/AArch64InstrFormats.td
index 9a2d220..6df7970 100644
--- a/llvm/lib/Target/AArch64/AArch64InstrFormats.td
+++ b/llvm/lib/Target/AArch64/AArch64InstrFormats.td
@@ -1647,6 +1647,8 @@ class BaseAuthLoad<bit M, bit W, dag oops, dag iops, string asm,
   let Inst{10} = 1;
   let Inst{9-5} = Rn;
   let Inst{4-0} = Rt;
+
+  let DecoderMethod = "DecodeAuthLoadInstruction";
 }
 
 multiclass AuthLoad<bit M, string asm, Operand opr> {
diff --git a/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp b/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
index d6db886..1ff4abb 100644
--- a/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
+++ b/llvm/lib/Target/AArch64/Disassembler/AArch64Disassembler.cpp
@@ -146,6 +146,9 @@ static DecodeStatus DecodeExclusiveLdStInstruction(MCInst &Inst, uint32_t insn,
 static DecodeStatus DecodePairLdStInstruction(MCInst &Inst, uint32_t insn,
                                               uint64_t Address,
                                               const void *Decoder);
+static DecodeStatus DecodeAuthLoadInstruction(MCInst &Inst, uint32_t insn,
+                                              uint64_t Address,
+                                              const void *Decoder);
 static DecodeStatus DecodeAddSubERegInstruction(MCInst &Inst, uint32_t insn,
                                                 uint64_t Address,
                                                 const void *Decoder);
@@ -1501,6 +1504,39 @@ static DecodeStatus DecodePairLdStInstruction(MCInst &Inst, uint32_t insn,
   return Success;
 }
 
+static DecodeStatus DecodeAuthLoadInstruction(MCInst &Inst, uint32_t insn,
+                                              uint64_t Addr,
+                                              const void *Decoder) {
+  unsigned Rt = fieldFromInstruction(insn, 0, 5);
+  unsigned Rn = fieldFromInstruction(insn, 5, 5);
+  uint64_t offset = fieldFromInstruction(insn, 22, 1) << 9 |
+                    fieldFromInstruction(insn, 12, 9);
+  unsigned writeback = fieldFromInstruction(insn, 11, 1);
+
+  switch (Inst.getOpcode()) {
+  default:
+    return Fail;
+  case AArch64::LDRAAwriteback:
+  case AArch64::LDRABwriteback:
+    DecodeGPR64spRegisterClass(Inst, Rn /* writeback register */, Addr,
+                               Decoder);
+    break;
+  case AArch64::LDRAAindexed:
+  case AArch64::LDRABindexed:
+    break;
+  }
+
+  DecodeGPR64RegisterClass(Inst, Rt, Addr, Decoder);
+  DecodeGPR64spRegisterClass(Inst, Rn, Addr, Decoder);
+  DecodeSImm<10>(Inst, offset, Addr, Decoder);
+
+  if (writeback && Rt == Rn && Rn != 31) {
+    return SoftFail;
+  }
+
+  return Success;
+}
+
 static DecodeStatus DecodeAddSubERegInstruction(MCInst &Inst, uint32_t insn,
                                                 uint64_t Addr,
                                                 const void *Decoder) {
diff --git a/llvm/test/MC/Disassembler/AArch64/armv8.3a-signed-pointer.txt b/llvm/test/MC/Disassembler/AArch64/armv8.3a-signed-pointer.txt
index 7215d08..110c668 100644
--- a/llvm/test/MC/Disassembler/AArch64/armv8.3a-signed-pointer.txt
+++ b/llvm/test/MC/Disassembler/AArch64/armv8.3a-signed-pointer.txt
@@ -1,4 +1,13 @@
-# RUN: llvm-mc -triple aarch64-none-linux-gnu -mattr=+v8.3a --disassemble < %s | FileCheck %s
+# RUN: llvm-mc -triple aarch64-none-linux-gnu -mattr=+v8.3a --disassemble < %s 2>&1 | FileCheck %s
+
+# CHECK: warning: potentially undefined instruction encoding
+# CHECK-NEXT: [0x00,0x0c,0x20,0xf8]
+# CHECK: warning: potentially undefined instruction encoding
+# CHECK-NEXT: [0x00,0x0c,0xa0,0xf8]
+# CHECK: ldraa x0, [x0, #0]!
+# CHECK: ldrab x0, [x0, #0]!
+[0x00,0x0c,0x20,0xf8]
+[0x00,0x0c,0xa0,0xf8]
 
 # CHECK: paciasp
 # CHECK: autiasp
-- 
2.7.4