[lldb][RISCV] fix LR/SC atomic sequence handling in lldb-server (#127505)

lldb-server had limited support for single-stepping through the lr/sc
atomic sequence. This patch enhances that support for all possible
atomic sequences.

lldb/source/Core/EmulateInstruction.cpp

@@ -588,7 +588,99 @@ EmulateInstruction::GetInternalRegisterNumber(RegisterContext *reg_ctx,
   return LLDB_INVALID_REGNUM;
 }
 
+std::unique_ptr<SingleStepBreakpointLocationsPredictor>
+EmulateInstruction::CreateBreakpointLocationPredictor(
+    std::unique_ptr<EmulateInstruction> emulator_up) {
+  auto creator =
+      emulator_up->GetSingleStepBreakpointLocationsPredictorCreator();
+  return creator(std::move(emulator_up));
+}
+
+std::optional<lldb::addr_t> EmulateInstruction::ReadPC() {
+  bool success = false;
+  auto addr = ReadRegisterUnsigned(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_PC,
+                                   LLDB_INVALID_ADDRESS, &success);
+  return success ? std::optional<addr_t>(addr) : std::nullopt;
+}
+
+bool EmulateInstruction::WritePC(lldb::addr_t addr) {
+  EmulateInstruction::Context ctx;
+  ctx.type = eContextAdvancePC;
+  ctx.SetNoArgs();
+  return WriteRegisterUnsigned(ctx, eRegisterKindGeneric,
+                               LLDB_REGNUM_GENERIC_PC, addr);
+}
+
 bool EmulateInstruction::CreateFunctionEntryUnwind(UnwindPlan &unwind_plan) {
   unwind_plan.Clear();
   return false;
 }
+
+BreakpointLocations
+SingleStepBreakpointLocationsPredictor::GetBreakpointLocations(Status &status) {
+  if (!m_emulator_up->ReadInstruction()) {
+    // try to get at least the size of next instruction to set breakpoint.
+    lldb::addr_t next_pc = GetNextInstructionAddress(status);
+    return BreakpointLocations{next_pc};
+  }
+
+  auto entry_pc = m_emulator_up->ReadPC();
+  if (!entry_pc) {
+    status = Status("Can't read PC");
+    return {};
+  }
+
+  m_emulation_result = m_emulator_up->EvaluateInstruction(
+      eEmulateInstructionOptionAutoAdvancePC);
+
+  lldb::addr_t next_pc = GetBreakpointLocationAddress(*entry_pc, status);
+  return BreakpointLocations{next_pc};
+}
+
+lldb::addr_t SingleStepBreakpointLocationsPredictor::GetNextInstructionAddress(
+    Status &error) {
+  auto instr_size = m_emulator_up->GetLastInstrSize();
+  if (!instr_size) {
+    error = Status("Read instruction failed!");
+    return LLDB_INVALID_ADDRESS;
+  }
+
+  auto pc = m_emulator_up->ReadPC();
+  if (!pc) {
+    error = Status("Can't read PC");
+    return LLDB_INVALID_ADDRESS;
+  }
+
+  lldb::addr_t next_pc = *pc + *instr_size;
+  return next_pc;
+}
+
+lldb::addr_t
+SingleStepBreakpointLocationsPredictor::GetBreakpointLocationAddress(
+    lldb::addr_t entry_pc, Status &error) {
+  auto addr = m_emulator_up->ReadPC();
+  if (!addr) {
+    error = Status("Can't read PC");
+    return LLDB_INVALID_ADDRESS;
+  }
+  lldb::addr_t pc = *addr;
+
+  if (m_emulation_result) {
+    assert(entry_pc != pc && "Emulation was successfull but PC wasn't updated");
+    return pc;
+  }
+
+  if (entry_pc == pc) {
+    // Emulate instruction failed and it hasn't changed PC. Advance PC with
+    // the size of the current opcode because the emulation of all
+    // PC modifying instruction should be successful. The failure most
+    // likely caused by an unsupported instruction which does not modify PC.
+    return pc + m_emulator_up->GetOpcode().GetByteSize();
+  }
+
+  // The instruction emulation failed after it modified the PC. It is an
+  // unknown error where we can't continue because the next instruction is
+  // modifying the PC but we don't  know how.
+  error = Status("Instruction emulation failed unexpectedly.");
+  return LLDB_INVALID_ADDRESS;
+}

lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp

@@ -14471,3 +14471,16 @@ bool EmulateInstructionARM::CreateFunctionEntryUnwind(UnwindPlan &unwind_plan) {
   unwind_plan.SetReturnAddressRegister(dwarf_lr);
   return true;
 }
+
+llvm::Expected<unsigned>
+ARMSingleStepBreakpointLocationsPredictor::GetBreakpointSize(
+    lldb::addr_t bp_addr) {
+  auto flags = m_emulator_up->ReadRegisterUnsigned(
+      eRegisterKindGeneric, LLDB_REGNUM_GENERIC_FLAGS, LLDB_INVALID_ADDRESS,
+      nullptr);
+  if (flags == LLDB_INVALID_ADDRESS)
+    return llvm::createStringError(llvm::inconvertibleErrorCode(),
+                                   "Reading flags failed!");
+
+  return (flags & 0x20) ? /* Thumb mode */ 2 : /* Arm mode */ 4;
+}

lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.h

@@ -16,6 +16,16 @@
 
 namespace lldb_private {
 
+class ARMSingleStepBreakpointLocationsPredictor
+    : public SingleStepBreakpointLocationsPredictor {
+public:
+  ARMSingleStepBreakpointLocationsPredictor(
+      std::unique_ptr<EmulateInstruction> emulator_up)
+      : SingleStepBreakpointLocationsPredictor{std::move(emulator_up)} {}
+
+  llvm::Expected<unsigned> GetBreakpointSize(lldb::addr_t bp_addr) override;
+};
+
 // ITSession - Keep track of the IT Block progression.
 class ITSession {
 public:
@@ -770,6 +780,14 @@ protected:
   // B6.2.13 SUBS PC, LR and related instructions
   bool EmulateSUBSPcLrEtc(const uint32_t opcode, const ARMEncoding encoding);
 
+  BreakpointLocationsPredictorCreator
+  GetSingleStepBreakpointLocationsPredictorCreator() override {
+    return [](std::unique_ptr<EmulateInstruction> emulator_up) {
+      return std::make_unique<ARMSingleStepBreakpointLocationsPredictor>(
+          std::move(emulator_up));
+    };
+  }
+
   uint32_t m_arm_isa;
   Mode m_opcode_mode;
   uint32_t m_opcode_cpsr;

lldb/source/Plugins/Instruction/LoongArch/EmulateInstructionLoongArch.cpp

@@ -86,7 +86,6 @@ bool EmulateInstructionLoongArch::EvaluateInstruction(uint32_t options) {
   uint32_t inst_size = m_opcode.GetByteSize();
   uint32_t inst = m_opcode.GetOpcode32();
   bool increase_pc = options & eEmulateInstructionOptionAutoAdvancePC;
-  bool success = false;
 
   Opcode *opcode_data = GetOpcodeForInstruction(inst);
   if (!opcode_data)
@@ -94,9 +93,10 @@ bool EmulateInstructionLoongArch::EvaluateInstruction(uint32_t options) {
 
   lldb::addr_t old_pc = 0;
   if (increase_pc) {
-    old_pc = ReadPC(&success);
-    if (!success)
+    auto addr = ReadPC();
+    if (!addr)
       return false;
+    old_pc = *addr;
   }
 
   // Call the Emulate... function.
@@ -104,9 +104,10 @@ bool EmulateInstructionLoongArch::EvaluateInstruction(uint32_t options) {
     return false;
 
   if (increase_pc) {
-    lldb::addr_t new_pc = ReadPC(&success);
-    if (!success)
+    auto addr = ReadPC();
+    if (!addr)
       return false;
+    lldb::addr_t new_pc = *addr;
 
     if (new_pc == old_pc && !WritePC(old_pc + inst_size))
       return false;
@@ -115,13 +116,14 @@ bool EmulateInstructionLoongArch::EvaluateInstruction(uint32_t options) {
 }
 
 bool EmulateInstructionLoongArch::ReadInstruction() {
-  bool success = false;
-  m_addr = ReadPC(&success);
-  if (!success) {
+  auto addr = ReadPC();
+  if (!addr) {
     m_addr = LLDB_INVALID_ADDRESS;
     return false;
   }
+  m_addr = *addr;
 
+  bool success = false;
   Context ctx;
   ctx.type = eContextReadOpcode;
   ctx.SetNoArgs();
@@ -131,19 +133,6 @@ bool EmulateInstructionLoongArch::ReadInstruction() {
   return true;
 }
 
-lldb::addr_t EmulateInstructionLoongArch::ReadPC(bool *success) {
-  return ReadRegisterUnsigned(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_PC,
-                              LLDB_INVALID_ADDRESS, success);
-}
-
-bool EmulateInstructionLoongArch::WritePC(lldb::addr_t pc) {
-  EmulateInstruction::Context ctx;
-  ctx.type = eContextAdvancePC;
-  ctx.SetNoArgs();
-  return WriteRegisterUnsigned(ctx, eRegisterKindGeneric,
-                               LLDB_REGNUM_GENERIC_PC, pc);
-}
-
 std::optional<RegisterInfo>
 EmulateInstructionLoongArch::GetRegisterInfo(lldb::RegisterKind reg_kind,
                                              uint32_t reg_index) {
@@ -273,9 +262,12 @@ bool EmulateInstructionLoongArch::EmulateNonJMP(uint32_t inst) { return false; }
 bool EmulateInstructionLoongArch::EmulateBEQZ64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint32_t offs21 = Bits32(inst, 25, 10) + (Bits32(inst, 4, 0) << 16);
   uint64_t rj_val = ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
@@ -293,9 +285,12 @@ bool EmulateInstructionLoongArch::EmulateBEQZ64(uint32_t inst) {
 bool EmulateInstructionLoongArch::EmulateBNEZ64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint32_t offs21 = Bits32(inst, 25, 10) + (Bits32(inst, 4, 0) << 16);
   uint64_t rj_val = ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
@@ -313,9 +308,12 @@ bool EmulateInstructionLoongArch::EmulateBNEZ64(uint32_t inst) {
 bool EmulateInstructionLoongArch::EmulateBCEQZ64(uint32_t inst) {
   bool success = false;
   uint32_t cj = Bits32(inst, 7, 5) + fpr_fcc0_loongarch;
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint32_t offs21 = Bits32(inst, 25, 10) + (Bits32(inst, 4, 0) << 16);
   uint8_t cj_val =
       (uint8_t)ReadRegisterUnsigned(eRegisterKindLLDB, cj, 0, &success);
@@ -335,9 +333,12 @@ bool EmulateInstructionLoongArch::EmulateBCEQZ64(uint32_t inst) {
 bool EmulateInstructionLoongArch::EmulateBCNEZ64(uint32_t inst) {
   bool success = false;
   uint32_t cj = Bits32(inst, 7, 5) + fpr_fcc0_loongarch;
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint32_t offs21 = Bits32(inst, 25, 10) + (Bits32(inst, 4, 0) << 16);
   uint8_t cj_val =
       (uint8_t)ReadRegisterUnsigned(eRegisterKindLLDB, cj, 0, &success);
@@ -358,9 +359,12 @@ bool EmulateInstructionLoongArch::EmulateJIRL64(uint32_t inst) {
   uint32_t rj = Bits32(inst, 9, 5);
   uint32_t rd = Bits32(inst, 4, 0);
   bool success = false;
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   EmulateInstruction::Context ctx;
   if (!WriteRegisterUnsigned(ctx, eRegisterKindLLDB, rd, pc + 4))
     return false;
@@ -374,10 +378,11 @@ bool EmulateInstructionLoongArch::EmulateJIRL64(uint32_t inst) {
 // b offs26
 // PC = PC + SignExtend({offs26, 2' b0}, GRLEN)
 bool EmulateInstructionLoongArch::EmulateB64(uint32_t inst) {
-  bool success = false;
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint32_t offs26 = Bits32(inst, 25, 10) + (Bits32(inst, 9, 0) << 16);
   uint64_t next_pc = pc + llvm::SignExtend64<28>(offs26 << 2);
   return WritePC(next_pc);
@@ -387,10 +392,11 @@ bool EmulateInstructionLoongArch::EmulateB64(uint32_t inst) {
 // GR[1] = PC + 4
 // PC = PC + SignExtend({offs26, 2'b0}, GRLEN)
 bool EmulateInstructionLoongArch::EmulateBL64(uint32_t inst) {
-  bool success = false;
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   EmulateInstruction::Context ctx;
   if (!WriteRegisterUnsigned(ctx, eRegisterKindLLDB, gpr_r1_loongarch, pc + 4))
     return false;
@@ -406,9 +412,12 @@ bool EmulateInstructionLoongArch::EmulateBEQ64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
   uint32_t rd = Bits32(inst, 4, 0);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint64_t rj_val = ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
     return false;
@@ -429,9 +438,12 @@ bool EmulateInstructionLoongArch::EmulateBNE64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
   uint32_t rd = Bits32(inst, 4, 0);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint64_t rj_val = ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
     return false;
@@ -452,9 +464,12 @@ bool EmulateInstructionLoongArch::EmulateBLT64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
   uint32_t rd = Bits32(inst, 4, 0);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   int64_t rj_val =
       (int64_t)ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
@@ -477,9 +492,12 @@ bool EmulateInstructionLoongArch::EmulateBGE64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
   uint32_t rd = Bits32(inst, 4, 0);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   int64_t rj_val =
       (int64_t)ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
@@ -502,9 +520,12 @@ bool EmulateInstructionLoongArch::EmulateBLTU64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
   uint32_t rd = Bits32(inst, 4, 0);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint64_t rj_val = ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
     return false;
@@ -525,9 +546,12 @@ bool EmulateInstructionLoongArch::EmulateBGEU64(uint32_t inst) {
   bool success = false;
   uint32_t rj = Bits32(inst, 9, 5);
   uint32_t rd = Bits32(inst, 4, 0);
-  uint64_t pc = ReadPC(&success);
-  if (!success)
+
+  auto addr = ReadPC();
+  if (!addr)
     return false;
+  uint64_t pc = *addr;
+
   uint64_t rj_val = ReadRegisterUnsigned(eRegisterKindLLDB, rj, 0, &success);
   if (!success)
     return false;

lldb/source/Plugins/Instruction/LoongArch/EmulateInstructionLoongArch.h

@@ -57,8 +57,6 @@ public:
 
   std::optional<RegisterInfo> GetRegisterInfo(lldb::RegisterKind reg_kind,
                                               uint32_t reg_num) override;
-  lldb::addr_t ReadPC(bool *success);
-  bool WritePC(lldb::addr_t pc);
   bool IsLoongArch64() { return m_arch_subtype == llvm::Triple::loongarch64; }
   bool TestExecute(uint32_t inst);
 

lldb/source/Plugins/Instruction/RISCV/EmulateInstructionRISCV.cpp

@@ -650,9 +650,10 @@ std::optional<DecodeResult> EmulateInstructionRISCV::Decode(uint32_t inst) {
   for (const InstrPattern &pat : PATTERNS) {
     if ((inst & pat.type_mask) == pat.eigen &&
         (inst_type & pat.inst_type) != 0) {
-      LLDB_LOGF(
-          log, "EmulateInstructionRISCV::%s: inst(%x at %" PRIx64 ") was decoded to %s",
-          __FUNCTION__, inst, m_addr, pat.name);
+      LLDB_LOGF(log,
+                "EmulateInstructionRISCV::%s: inst(%x at %" PRIx64
+                ") was decoded to %s",
+                __FUNCTION__, inst, m_addr, pat.name);
       auto decoded = is_16b ? pat.decode(try_rvc) : pat.decode(inst);
       return DecodeResult{decoded, inst, is_16b, pat};
     }
@@ -1649,21 +1650,6 @@ bool EmulateInstructionRISCV::ReadInstruction() {
   return true;
 }
 
-std::optional<addr_t> EmulateInstructionRISCV::ReadPC() {
-  bool success = false;
-  auto addr = ReadRegisterUnsigned(eRegisterKindGeneric, LLDB_REGNUM_GENERIC_PC,
-                                   LLDB_INVALID_ADDRESS, &success);
-  return success ? std::optional<addr_t>(addr) : std::nullopt;
-}
-
-bool EmulateInstructionRISCV::WritePC(addr_t pc) {
-  EmulateInstruction::Context ctx;
-  ctx.type = eContextAdvancePC;
-  ctx.SetNoArgs();
-  return WriteRegisterUnsigned(ctx, eRegisterKindGeneric,
-                               LLDB_REGNUM_GENERIC_PC, pc);
-}
-
 RoundingMode EmulateInstructionRISCV::GetRoundingMode() {
   bool success = false;
   auto fcsr = ReadRegisterUnsigned(eRegisterKindLLDB, fpr_fcsr_riscv,
@@ -1792,4 +1778,128 @@ bool EmulateInstructionRISCV::SupportsThisArch(const ArchSpec &arch) {
   return arch.GetTriple().isRISCV();
 }
 
+BreakpointLocations
+RISCVSingleStepBreakpointLocationsPredictor::GetBreakpointLocations(
+    Status &status) {
+  EmulateInstructionRISCV *riscv_emulator =
+      static_cast<EmulateInstructionRISCV *>(m_emulator_up.get());
+
+  auto pc = riscv_emulator->ReadPC();
+  if (!pc) {
+    status = Status("Can't read PC");
+    return {};
+  }
+
+  auto inst = riscv_emulator->ReadInstructionAt(*pc);
+  if (!inst) {
+    // Can't read instruction. Try default handler.
+    return SingleStepBreakpointLocationsPredictor::GetBreakpointLocations(
+        status);
+  }
+
+  if (FoundLoadReserve(inst->decoded))
+    return HandleAtomicSequence(*pc, status);
+
+  if (FoundStoreConditional(inst->decoded)) {
+    // Ill-formed atomic sequence (SC doesn't have corresponding LR
+    // instruction). Consider SC instruction like a non-atomic store and set a
+    // breakpoint at the next instruction.
+    Log *log = GetLog(LLDBLog::Unwind);
+    LLDB_LOGF(log,
+              "RISCVSingleStepBreakpointLocationsPredictor::%s: can't find "
+              "corresponding load reserve insturuction",
+              __FUNCTION__);
+    return {*pc + (inst->is_rvc ? 2u : 4u)};
+  }
+
+  return SingleStepBreakpointLocationsPredictor::GetBreakpointLocations(status);
+}
+
+llvm::Expected<unsigned>
+RISCVSingleStepBreakpointLocationsPredictor::GetBreakpointSize(
+    lldb::addr_t bp_addr) {
+  EmulateInstructionRISCV *riscv_emulator =
+      static_cast<EmulateInstructionRISCV *>(m_emulator_up.get());
+
+  if (auto inst = riscv_emulator->ReadInstructionAt(bp_addr); inst)
+    return inst->is_rvc ? 2 : 4;
+
+  // Try last instruction size.
+  if (auto last_instr_size = riscv_emulator->GetLastInstrSize();
+      last_instr_size)
+    return *last_instr_size;
+
+  // Just place non-compressed software trap.
+  return 4;
+}
+
+BreakpointLocations
+RISCVSingleStepBreakpointLocationsPredictor::HandleAtomicSequence(
+    lldb::addr_t pc, Status &error) {
+  EmulateInstructionRISCV *riscv_emulator =
+      static_cast<EmulateInstructionRISCV *>(m_emulator_up.get());
+
+  // Handle instructions between LR and SC. According to unprivilleged
+  // RISC-V ISA there can be at most 16 instructions in the sequence.
+
+  lldb::addr_t entry_pc = pc; // LR instruction address
+  auto lr_inst = riscv_emulator->ReadInstructionAt(entry_pc);
+  pc += lr_inst->is_rvc ? 2 : 4;
+
+  size_t atomic_length = 0;
+  std::optional<DecodeResult> inst;
+  std::vector<lldb::addr_t> bp_addrs;
+  do {
+    inst = riscv_emulator->ReadInstructionAt(pc);
+    if (!inst) {
+      error = Status("Can't read instruction");
+      return {};
+    }
+
+    if (B *branch = std::get_if<B>(&inst->decoded))
+      bp_addrs.push_back(pc + SignExt(branch->imm));
+
+    unsigned addent = inst->is_rvc ? 2 : 4;
+    pc += addent;
+    atomic_length += addent;
+  } while ((atomic_length < s_max_atomic_sequence_length) &&
+           !FoundStoreConditional(inst->decoded));
+
+  if (atomic_length >= s_max_atomic_sequence_length) {
+    // Ill-formed atomic sequence (LR doesn't have corresponding SC
+    // instruction). In this case consider LR like a non-atomic load instruction
+    // and set a breakpoint at the next after LR instruction.
+    Log *log = GetLog(LLDBLog::Unwind);
+    LLDB_LOGF(log,
+              "RISCVSingleStepBreakpointLocationsPredictor::%s: can't find "
+              "corresponding store conditional insturuction",
+              __FUNCTION__);
+    return {entry_pc + (lr_inst->is_rvc ? 2u : 4u)};
+  }
+
+  lldb::addr_t exit_pc = pc;
+
+  // Check if we have a branch to the start of the atomic sequence after SC
+  // instruction. If we have such branch, consider it as a part of the atomic
+  // sequence.
+  inst = riscv_emulator->ReadInstructionAt(exit_pc);
+  if (inst) {
+    B *branch = std::get_if<B>(&inst->decoded);
+    if (branch && (exit_pc + SignExt(branch->imm)) == entry_pc)
+      exit_pc += inst->is_rvc ? 2 : 4;
+  }
+
+  // Set breakpoints at the jump addresses of the forward branches that points
+  // after the end of the atomic sequence.
+  bp_addrs.erase(llvm::remove_if(bp_addrs,
+                                 [exit_pc](lldb::addr_t bp_addr) {
+                                   return exit_pc >= bp_addr;
+                                 }),
+                 bp_addrs.end());
+
+  // Set breakpoint at the end of atomic sequence.
+  bp_addrs.push_back(exit_pc);
+  return bp_addrs;
+}
+
 } // namespace lldb_private

lldb/source/Plugins/Instruction/RISCV/EmulateInstructionRISCV.h

@@ -20,6 +20,33 @@
 
 namespace lldb_private {
 
+class RISCVSingleStepBreakpointLocationsPredictor
+    : public SingleStepBreakpointLocationsPredictor {
+public:
+  RISCVSingleStepBreakpointLocationsPredictor(
+      std::unique_ptr<EmulateInstruction> emulator)
+      : SingleStepBreakpointLocationsPredictor{std::move(emulator)} {}
+
+  BreakpointLocations GetBreakpointLocations(Status &status) override;
+
+  llvm::Expected<unsigned> GetBreakpointSize(lldb::addr_t bp_addr) override;
+
+private:
+  static bool FoundLoadReserve(const RISCVInst &inst) {
+    return std::holds_alternative<LR_W>(inst) ||
+           std::holds_alternative<LR_D>(inst);
+  }
+
+  static bool FoundStoreConditional(const RISCVInst &inst) {
+    return std::holds_alternative<SC_W>(inst) ||
+           std::holds_alternative<SC_D>(inst);
+  }
+
+  BreakpointLocations HandleAtomicSequence(lldb::addr_t pc, Status &error);
+
+  static constexpr size_t s_max_atomic_sequence_length = 64;
+};
+
 class EmulateInstructionRISCV : public EmulateInstruction {
 public:
   static llvm::StringRef GetPluginNameStatic() { return "riscv"; }
@@ -67,9 +94,6 @@ public:
   std::optional<RegisterInfo> GetRegisterInfo(lldb::RegisterKind reg_kind,
                                               uint32_t reg_num) override;
 
-  std::optional<lldb::addr_t> ReadPC();
-  bool WritePC(lldb::addr_t pc);
-
   std::optional<DecodeResult> ReadInstructionAt(lldb::addr_t addr);
   std::optional<DecodeResult> Decode(uint32_t inst);
   bool Execute(DecodeResult inst, bool ignore_cond);
@@ -98,6 +122,13 @@ public:
   bool SetAccruedExceptions(llvm::APFloatBase::opStatus);
 
 private:
+  BreakpointLocationsPredictorCreator
+  GetSingleStepBreakpointLocationsPredictorCreator() override {
+    return [](std::unique_ptr<EmulateInstruction> emulator_up) {
+      return std::make_unique<RISCVSingleStepBreakpointLocationsPredictor>(
+          std::move(emulator_up));
+    };
+  }
   /// Last decoded instruction from m_opcode
   DecodeResult m_decoded;
   /// Last decoded instruction size estimate.

lldb/source/Plugins/Process/FreeBSD/NativeProcessFreeBSD.cpp

@@ -324,12 +324,14 @@ void NativeProcessFreeBSD::MonitorSIGTRAP(lldb::pid_t pid) {
         auto thread_info =
             m_threads_stepping_with_breakpoint.find(thread->GetID());
         if (thread_info != m_threads_stepping_with_breakpoint.end() &&
-            thread_info->second == regctx.GetPC()) {
+            llvm::is_contained(thread_info->second, regctx.GetPC())) {
           thread->SetStoppedByTrace();
-          Status brkpt_error = RemoveBreakpoint(thread_info->second);
-          if (brkpt_error.Fail())
-            LLDB_LOG(log, "pid = {0} remove stepping breakpoint: {1}",
-                     thread_info->first, brkpt_error);
+          for (auto &&bp_addr : thread_info->second) {
+            Status brkpt_error = RemoveBreakpoint(bp_addr);
+            if (brkpt_error.Fail())
+              LLDB_LOG(log, "pid = {0} remove stepping breakpoint: {1}",
+                       thread_info->first, brkpt_error);
+          }
           m_threads_stepping_with_breakpoint.erase(thread_info);
         } else
           thread->SetStoppedByBreakpoint();

lldb/source/Plugins/Process/Linux/NativeProcessLinux.cpp

@@ -833,7 +833,7 @@ void NativeProcessLinux::MonitorBreakpoint(NativeThreadLinux &thread) {
   auto stepping_with_bp_it =
       m_threads_stepping_with_breakpoint.find(thread.GetID());
   if (stepping_with_bp_it != m_threads_stepping_with_breakpoint.end() &&
-      stepping_with_bp_it->second == reg_ctx.GetPC())
+      llvm::is_contained(stepping_with_bp_it->second, reg_ctx.GetPC()))
     thread.SetStoppedByTrace();
 
   StopRunningThreads(thread.GetID());
@@ -1960,10 +1960,12 @@ void NativeProcessLinux::SignalIfAllThreadsStopped() {
   // Clear any temporary breakpoints we used to implement software single
   // stepping.
   for (const auto &thread_info : m_threads_stepping_with_breakpoint) {
-    Status error = RemoveBreakpoint(thread_info.second);
-    if (error.Fail())
-      LLDB_LOG(log, "pid = {0} remove stepping breakpoint: {1}",
-               thread_info.first, error);
+    for (auto &&bp_addr : thread_info.second) {
+      Status error = RemoveBreakpoint(bp_addr);
+      if (error.Fail())
+        LLDB_LOG(log, "pid = {0} remove stepping breakpoint: {1}",
+                 thread_info.first, error);
+    }
   }
   m_threads_stepping_with_breakpoint.clear();
 

lldb/source/Plugins/Process/Utility/NativeProcessSoftwareSingleStep.cpp

@@ -87,34 +87,10 @@ static size_t WriteMemoryCallback(EmulateInstruction *instruction, void *baton,
   return length;
 }
 
-static lldb::addr_t ReadFlags(NativeRegisterContext &regsiter_context) {
-  const RegisterInfo *flags_info = regsiter_context.GetRegisterInfo(
-      eRegisterKindGeneric, LLDB_REGNUM_GENERIC_FLAGS);
-  return regsiter_context.ReadRegisterAsUnsigned(flags_info,
-                                                 LLDB_INVALID_ADDRESS);
-}
-
-static int GetSoftwareBreakpointSize(const ArchSpec &arch,
-                                     lldb::addr_t next_flags) {
-  if (arch.GetMachine() == llvm::Triple::arm) {
-    if (next_flags & 0x20)
-      // Thumb mode
-      return 2;
-    // Arm mode
-    return 4;
-  }
-  if (arch.IsMIPS() || arch.GetTriple().isPPC64() ||
-      arch.GetTriple().isRISCV() || arch.GetTriple().isLoongArch())
-    return 4;
-  return 0;
-}
-
-static Status SetSoftwareBreakpointOnPC(const ArchSpec &arch, lldb::addr_t pc,
-                                        lldb::addr_t next_flags,
-                                        NativeProcessProtocol &process) {
-  int size_hint = GetSoftwareBreakpointSize(arch, next_flags);
+static Status SetSoftwareBreakpoint(lldb::addr_t bp_addr, unsigned bp_size,
+                                    NativeProcessProtocol &process) {
   Status error;
-  error = process.SetBreakpoint(pc, size_hint, /*hardware=*/false);
+  error = process.SetBreakpoint(bp_addr, bp_size, /*hardware=*/false);
 
   // If setting the breakpoint fails because pc is out of the address
   // space, ignore it and let the debugee segfault.
@@ -136,7 +112,6 @@ Status NativeProcessSoftwareSingleStep::SetupSoftwareSingleStepping(
   std::unique_ptr<EmulateInstruction> emulator_up(
       EmulateInstruction::FindPlugin(arch, eInstructionTypePCModifying,
                                      nullptr));
-
   if (emulator_up == nullptr)
     return Status::FromErrorString("Instruction emulator not found!");
 
@@ -147,65 +122,24 @@ Status NativeProcessSoftwareSingleStep::SetupSoftwareSingleStepping(
   emulator_up->SetWriteMemCallback(&WriteMemoryCallback);
   emulator_up->SetWriteRegCallback(&WriteRegisterCallback);
 
-  if (!emulator_up->ReadInstruction()) {
-    // try to get at least the size of next instruction to set breakpoint.
-    auto instr_size = emulator_up->GetLastInstrSize();
-    if (!instr_size)
-      return Status::FromErrorString("Read instruction failed!");
-    bool success = false;
-    auto pc = emulator_up->ReadRegisterUnsigned(eRegisterKindGeneric,
-                                                LLDB_REGNUM_GENERIC_PC,
-                                                LLDB_INVALID_ADDRESS, &success);
-    if (!success)
-      return Status::FromErrorString("Reading pc failed!");
-    lldb::addr_t next_pc = pc + *instr_size;
-    auto result =
-        SetSoftwareBreakpointOnPC(arch, next_pc, /* next_flags */ 0x0, process);
-    m_threads_stepping_with_breakpoint.insert({thread.GetID(), next_pc});
-    return result;
+  auto bp_locaions_predictor =
+      EmulateInstruction::CreateBreakpointLocationPredictor(
+          std::move(emulator_up));
+
+  auto bp_locations = bp_locaions_predictor->GetBreakpointLocations(error);
+  if (error.Fail())
+    return error;
+
+  for (auto &&bp_addr : bp_locations) {
+    auto bp_size = bp_locaions_predictor->GetBreakpointSize(bp_addr);
+    if (auto err = bp_size.takeError())
+      return Status(toString(std::move(err)));
+
+    error = SetSoftwareBreakpoint(bp_addr, *bp_size, process);
+    if (error.Fail())
+      return error;
   }
 
-  bool emulation_result =
-      emulator_up->EvaluateInstruction(eEmulateInstructionOptionAutoAdvancePC);
-
-  const RegisterInfo *reg_info_pc = register_context.GetRegisterInfo(
-      eRegisterKindGeneric, LLDB_REGNUM_GENERIC_PC);
-  const RegisterInfo *reg_info_flags = register_context.GetRegisterInfo(
-      eRegisterKindGeneric, LLDB_REGNUM_GENERIC_FLAGS);
-
-  auto pc_it =
-      baton.m_register_values.find(reg_info_pc->kinds[eRegisterKindDWARF]);
-  auto flags_it = reg_info_flags == nullptr
-                      ? baton.m_register_values.end()
-                      : baton.m_register_values.find(
-                            reg_info_flags->kinds[eRegisterKindDWARF]);
-
-  lldb::addr_t next_pc;
-  lldb::addr_t next_flags;
-  if (emulation_result) {
-    assert(pc_it != baton.m_register_values.end() &&
-           "Emulation was successfull but PC wasn't updated");
-    next_pc = pc_it->second.GetAsUInt64();
-
-    if (flags_it != baton.m_register_values.end())
-      next_flags = flags_it->second.GetAsUInt64();
-    else
-      next_flags = ReadFlags(register_context);
-  } else if (pc_it == baton.m_register_values.end()) {
-    // Emulate instruction failed and it haven't changed PC. Advance PC with
-    // the size of the current opcode because the emulation of all
-    // PC modifying instruction should be successful. The failure most
-    // likely caused by a not supported instruction which don't modify PC.
-    next_pc = register_context.GetPC() + emulator_up->GetOpcode().GetByteSize();
-    next_flags = ReadFlags(register_context);
-  } else {
-    // The instruction emulation failed after it modified the PC. It is an
-    // unknown error where we can't continue because the next instruction is
-    // modifying the PC but we don't  know how.
-    return Status::FromErrorString(
-        "Instruction emulation failed unexpectedly.");
-  }
-  auto result = SetSoftwareBreakpointOnPC(arch, next_pc, next_flags, process);
-  m_threads_stepping_with_breakpoint.insert({thread.GetID(), next_pc});
-  return result;
+  m_threads_stepping_with_breakpoint.insert({thread.GetID(), bp_locations});
+  return error;
 }

lldb/source/Plugins/Process/Utility/NativeProcessSoftwareSingleStep.h

@@ -23,7 +23,8 @@ public:
 protected:
   // List of thread ids stepping with a breakpoint with the address of
   // the relevan breakpoint
-  std::map<lldb::tid_t, lldb::addr_t> m_threads_stepping_with_breakpoint;
+  std::map<lldb::tid_t, std::vector<lldb::addr_t>>
+      m_threads_stepping_with_breakpoint;
 };
 
 } // namespace lldb_private