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ArchitectureArm.cpp
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1 //===-- ArchitectureArm.cpp -----------------------------------------------===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 
14 #include "lldb/Target/Thread.h"
15 #include "lldb/Utility/ArchSpec.h"
16 
17 using namespace lldb_private;
18 using namespace lldb;
19 
21 
22 void ArchitectureArm::Initialize() {
23  PluginManager::RegisterPlugin(GetPluginNameStatic(),
24  "Arm-specific algorithms",
26 }
27 
30 }
31 
32 std::unique_ptr<Architecture> ArchitectureArm::Create(const ArchSpec &arch) {
33  if (arch.GetMachine() != llvm::Triple::arm)
34  return nullptr;
35  return std::unique_ptr<Architecture>(new ArchitectureArm());
36 }
37 
39  // We need to check if we are stopped in Thumb mode in a IT instruction and
40  // detect if the condition doesn't pass. If this is the case it means we
41  // won't actually execute this instruction. If this happens we need to clear
42  // the stop reason to no thread plans think we are stopped for a reason and
43  // the plans should keep going.
44  //
45  // We do this because when single stepping many ARM processes, debuggers
46  // often use the BVR/BCR registers that says "stop when the PC is not equal
47  // to its current value". This method of stepping means we can end up
48  // stopping on instructions inside an if/then block that wouldn't get
49  // executed. By fixing this we can stop the debugger from seeming like you
50  // stepped through both the "if" _and_ the "else" clause when source level
51  // stepping because the debugger stops regardless due to the BVR/BCR
52  // triggering a stop.
53  //
54  // It also means we can set breakpoints on instructions inside an an if/then
55  // block and correctly skip them if we use the BKPT instruction. The ARM and
56  // Thumb BKPT instructions are unconditional even when executed in a Thumb IT
57  // block.
58  //
59  // If your debugger inserts software traps in ARM/Thumb code, it will need to
60  // use 16 and 32 bit instruction for 16 and 32 bit thumb instructions
61  // respectively. If your debugger inserts a 16 bit thumb trap on top of a 32
62  // bit thumb instruction for an opcode that is inside an if/then, it will
63  // change the it/then to conditionally execute your
64  // 16 bit trap and then cause your program to crash if it executes the
65  // trailing 16 bits (the second half of the 32 bit thumb instruction you
66  // partially overwrote).
67 
68  RegisterContextSP reg_ctx_sp(thread.GetRegisterContext());
69  if (!reg_ctx_sp)
70  return;
71 
72  const uint32_t cpsr = reg_ctx_sp->GetFlags(0);
73  if (cpsr == 0)
74  return;
75 
76  // Read the J and T bits to get the ISETSTATE
77  const uint32_t J = Bit32(cpsr, 24);
78  const uint32_t T = Bit32(cpsr, 5);
79  const uint32_t ISETSTATE = J << 1 | T;
80  if (ISETSTATE == 0) {
81 // NOTE: I am pretty sure we want to enable the code below
82 // that detects when we stop on an instruction in ARM mode that is conditional
83 // and the condition doesn't pass. This can happen if you set a breakpoint on
84 // an instruction that is conditional. We currently will _always_ stop on the
85 // instruction which is bad. You can also run into this while single stepping
86 // and you could appear to run code in the "if" and in the "else" clause
87 // because it would stop at all of the conditional instructions in both. In
88 // such cases, we really don't want to stop at this location.
89 // I will check with the lldb-dev list first before I enable this.
90 #if 0
91  // ARM mode: check for condition on instruction
92  const addr_t pc = reg_ctx_sp->GetPC();
93  Status error;
94  // If we fail to read the opcode we will get UINT64_MAX as the result in
95  // "opcode" which we can use to detect if we read a valid opcode.
96  const uint64_t opcode = thread.GetProcess()->ReadUnsignedIntegerFromMemory(pc, 4, UINT64_MAX, error);
97  if (opcode <= UINT32_MAX)
98  {
99  const uint32_t condition = Bits32((uint32_t)opcode, 31, 28);
100  if (!ARMConditionPassed(condition, cpsr))
101  {
102  // We ARE stopped on an ARM instruction whose condition doesn't
103  // pass so this instruction won't get executed. Regardless of why
104  // it stopped, we need to clear the stop info
105  thread.SetStopInfo (StopInfoSP());
106  }
107  }
108 #endif
109  } else if (ISETSTATE == 1) {
110  // Thumb mode
111  const uint32_t ITSTATE = Bits32(cpsr, 15, 10) << 2 | Bits32(cpsr, 26, 25);
112  if (ITSTATE != 0) {
113  const uint32_t condition = Bits32(ITSTATE, 7, 4);
114  if (!ARMConditionPassed(condition, cpsr)) {
115  // We ARE stopped in a Thumb IT instruction on an instruction whose
116  // condition doesn't pass so this instruction won't get executed.
117  // Regardless of why it stopped, we need to clear the stop info
118  thread.SetStopInfo(StopInfoSP());
119  }
120  }
121  }
122 }
123 
125  AddressClass addr_class) const {
126  bool is_alternate_isa = false;
127 
128  switch (addr_class) {
129  case AddressClass::eData:
131  return LLDB_INVALID_ADDRESS;
133  is_alternate_isa = true;
134  break;
135  default: break;
136  }
137 
138  if ((code_addr & 2u) || is_alternate_isa)
139  return code_addr | 1u;
140  return code_addr;
141 }
142 
144  AddressClass addr_class) const {
145  switch (addr_class) {
146  case AddressClass::eData:
148  return LLDB_INVALID_ADDRESS;
149  default: break;
150  }
151  return opcode_addr & ~(1ull);
152 }
lldb_private::AddressClass::eData
@ eData
ArchitectureArm.h
lldb_private::ArchSpec
Definition: ArchSpec.h:33
lldb_private::ArchitectureArm::OverrideStopInfo
void OverrideStopInfo(Thread &thread) const override
This is currently intended to handle cases where a program stops at an instruction that won't get exe...
Definition: ArchitectureArm.cpp:38
lldb_private::ArchSpec::GetMachine
llvm::Triple::ArchType GetMachine() const
Returns a machine family for the current architecture.
Definition: ArchSpec.cpp:668
lldb_private::AddressClass
AddressClass
Definition: lldb-private-enumerations.h:48
arm64_dwarf::cpsr
@ cpsr
Definition: ARM64_DWARF_Registers.h:53
lldb_private::ArchitectureArm::GetCallableLoadAddress
lldb::addr_t GetCallableLoadAddress(lldb::addr_t load_addr, AddressClass addr_class) const override
Get load_addr as a callable code load address for this target.
Definition: ArchitectureArm.cpp:124
lldb::addr_t
uint64_t addr_t
Definition: lldb-types.h:83
pc
@ pc
Definition: CompactUnwindInfo.cpp:1251
lldb_private::Thread::GetProcess
lldb::ProcessSP GetProcess() const
Definition: Thread.h:153
error
static llvm::raw_ostream & error(Stream &strm)
Definition: CommandReturnObject.cpp:17
lldb_private::PluginManager::UnregisterPlugin
static bool UnregisterPlugin(ABICreateInstance create_callback)
Definition: PluginManager.cpp:293
lldb_private::Bit32
static uint32_t Bit32(const uint32_t bits, const uint32_t bit)
Definition: InstructionUtils.h:36
lldb_private::Thread
Definition: Thread.h:61
lldb_private::ArchitectureArm
Definition: ArchitectureArm.h:16
lldb_private::Thread::SetStopInfo
void SetStopInfo(const lldb::StopInfoSP &stop_info_sp)
Definition: Thread.cpp:435
lldb_private::ArchitectureArm::GetOpcodeLoadAddress
lldb::addr_t GetOpcodeLoadAddress(lldb::addr_t load_addr, AddressClass addr_class) const override
Get load_addr as an opcode for this target.
Definition: ArchitectureArm.cpp:143
ARMDefines.h
Thread.h
InstructionUtils.h
lldb_private::Status
Definition: Status.h:44
lldb_private::ArchitectureArm::Create
static std::unique_ptr< Architecture > Create(const ArchSpec &arch)
Definition: ArchitectureArm.cpp:32
uint32_t
ArchSpec.h
UINT32_MAX
#define UINT32_MAX
Definition: lldb-defines.h:19
PluginManager.h
lldb_private::ARMConditionPassed
static bool ARMConditionPassed(const uint32_t condition, const uint32_t cpsr)
Definition: ARMDefines.h:107
LLDB_INVALID_ADDRESS
#define LLDB_INVALID_ADDRESS
Definition: lldb-defines.h:74
lldb_private::AddressClass::eDebug
@ eDebug
lldb_private::AddressClass::eCodeAlternateISA
@ eCodeAlternateISA
lldb_private::PluginManager::RegisterPlugin
static bool RegisterPlugin(llvm::StringRef name, llvm::StringRef description, ABICreateInstance create_callback)
Definition: PluginManager.cpp:287
lldb_private
A class that represents a running process on the host machine.
Definition: SBCommandInterpreterRunOptions.h:16
lldb_private::ArchitectureArm::Terminate
static void Terminate()
Definition: ArchitectureArm.cpp:28
LLDB_PLUGIN_DEFINE
#define LLDB_PLUGIN_DEFINE(PluginName)
Definition: PluginManager.h:31
lldb_private::Thread::GetRegisterContext
virtual lldb::RegisterContextSP GetRegisterContext()=0
lldb
Definition: SBAddress.h:15
RegisterContext.h
UINT64_MAX
#define UINT64_MAX
Definition: lldb-defines.h:23
lldb_private::Bits32
static uint32_t Bits32(const uint32_t bits, const uint32_t msbit, const uint32_t lsbit)
Definition: InstructionUtils.h:29