From 4dcd1d18599e46cfb6cf945026d7ce58b33a72bf Mon Sep 17 00:00:00 2001
From: MerryMage <MerryMage@users.noreply.github.com>
Date: Sun, 7 Aug 2016 20:50:33 +0100
Subject: [PATCH] Arm: BLX is UNPREDICTABLE when Rm is PC

---
 src/frontend/translate/translate_arm/branch.cpp | 2 ++
 tests/arm/fuzz_arm.cpp                          | 3 ++-
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/src/frontend/translate/translate_arm/branch.cpp b/src/frontend/translate/translate_arm/branch.cpp
index 4a061b07..36ce9b20 100644
--- a/src/frontend/translate/translate_arm/branch.cpp
+++ b/src/frontend/translate/translate_arm/branch.cpp
@@ -44,6 +44,8 @@ bool ArmTranslatorVisitor::arm_BLX_imm(bool H, Imm24 imm24) {
 }
 
 bool ArmTranslatorVisitor::arm_BLX_reg(Cond cond, Reg m) {
+    if (m == Reg::PC)
+        return UnpredictableInstruction();
     // BLX <Rm>
     if (ConditionPassed(cond)) {
         ir.SetRegister(Reg::LR, ir.Imm32(ir.current_location.PC() + 4));
diff --git a/tests/arm/fuzz_arm.cpp b/tests/arm/fuzz_arm.cpp
index 10397f70..6f64c463 100644
--- a/tests/arm/fuzz_arm.cpp
+++ b/tests/arm/fuzz_arm.cpp
@@ -563,7 +563,8 @@ TEST_CASE("Fuzz ARM data processing instructions", "[JitX64]") {
 TEST_CASE("Fuzz ARM branch instructions", "[JitX64]") {
     const std::array<InstructionGenerator, 6> instructions = {{
         InstructionGenerator("1111101hvvvvvvvvvvvvvvvvvvvvvvvv"),
-        InstructionGenerator("cccc000100101111111111110011mmmm"),
+        InstructionGenerator("cccc000100101111111111110011mmmm",
+                             [](u32 instr) { return Bits<0, 3>(instr) != 0b1111; }), // R15 is UNPREDICTABLE
         InstructionGenerator("cccc1010vvvvvvvvvvvvvvvvvvvvvvvv"),
         InstructionGenerator("cccc1011vvvvvvvvvvvvvvvvvvvvvvvv"),
         InstructionGenerator("cccc000100101111111111110001mmmm"),