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ArchitectureArm.cpp
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1 //===-- ArchitectureArm.cpp -------------------------------------*- C++ -*-===//
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  return ConstString("arm");
22 }
23 
25  PluginManager::RegisterPlugin(GetPluginNameStatic(),
26  "Arm-specific algorithms",
27  &ArchitectureArm::Create);
28 }
29 
31  PluginManager::UnregisterPlugin(&ArchitectureArm::Create);
32 }
33 
34 std::unique_ptr<Architecture> ArchitectureArm::Create(const ArchSpec &arch) {
35  if (arch.GetMachine() != llvm::Triple::arm)
36  return nullptr;
37  return std::unique_ptr<Architecture>(new ArchitectureArm());
38 }
39 
40 ConstString ArchitectureArm::GetPluginName() { return GetPluginNameStatic(); }
42 
44  // We need to check if we are stopped in Thumb mode in a IT instruction and
45  // detect if the condition doesn't pass. If this is the case it means we
46  // won't actually execute this instruction. If this happens we need to clear
47  // the stop reason to no thread plans think we are stopped for a reason and
48  // the plans should keep going.
49  //
50  // We do this because when single stepping many ARM processes, debuggers
51  // often use the BVR/BCR registers that says "stop when the PC is not equal
52  // to its current value". This method of stepping means we can end up
53  // stopping on instructions inside an if/then block that wouldn't get
54  // executed. By fixing this we can stop the debugger from seeming like you
55  // stepped through both the "if" _and_ the "else" clause when source level
56  // stepping because the debugger stops regardless due to the BVR/BCR
57  // triggering a stop.
58  //
59  // It also means we can set breakpoints on instructions inside an an if/then
60  // block and correctly skip them if we use the BKPT instruction. The ARM and
61  // Thumb BKPT instructions are unconditional even when executed in a Thumb IT
62  // block.
63  //
64  // If your debugger inserts software traps in ARM/Thumb code, it will need to
65  // use 16 and 32 bit instruction for 16 and 32 bit thumb instructions
66  // respectively. If your debugger inserts a 16 bit thumb trap on top of a 32
67  // bit thumb instruction for an opcode that is inside an if/then, it will
68  // change the it/then to conditionally execute your
69  // 16 bit trap and then cause your program to crash if it executes the
70  // trailing 16 bits (the second half of the 32 bit thumb instruction you
71  // partially overwrote).
72 
73  RegisterContextSP reg_ctx_sp(thread.GetRegisterContext());
74  if (!reg_ctx_sp)
75  return;
76 
77  const uint32_t cpsr = reg_ctx_sp->GetFlags(0);
78  if (cpsr == 0)
79  return;
80 
81  // Read the J and T bits to get the ISETSTATE
82  const uint32_t J = Bit32(cpsr, 24);
83  const uint32_t T = Bit32(cpsr, 5);
84  const uint32_t ISETSTATE = J << 1 | T;
85  if (ISETSTATE == 0) {
86 // NOTE: I am pretty sure we want to enable the code below
87 // that detects when we stop on an instruction in ARM mode that is conditional
88 // and the condition doesn't pass. This can happen if you set a breakpoint on
89 // an instruction that is conditional. We currently will _always_ stop on the
90 // instruction which is bad. You can also run into this while single stepping
91 // and you could appear to run code in the "if" and in the "else" clause
92 // because it would stop at all of the conditional instructions in both. In
93 // such cases, we really don't want to stop at this location.
94 // I will check with the lldb-dev list first before I enable this.
95 #if 0
96  // ARM mode: check for condition on instruction
97  const addr_t pc = reg_ctx_sp->GetPC();
98  Status error;
99  // If we fail to read the opcode we will get UINT64_MAX as the result in
100  // "opcode" which we can use to detect if we read a valid opcode.
101  const uint64_t opcode = thread.GetProcess()->ReadUnsignedIntegerFromMemory(pc, 4, UINT64_MAX, error);
102  if (opcode <= UINT32_MAX)
103  {
104  const uint32_t condition = Bits32((uint32_t)opcode, 31, 28);
105  if (!ARMConditionPassed(condition, cpsr))
106  {
107  // We ARE stopped on an ARM instruction whose condition doesn't
108  // pass so this instruction won't get executed. Regardless of why
109  // it stopped, we need to clear the stop info
110  thread.SetStopInfo (StopInfoSP());
111  }
112  }
113 #endif
114  } else if (ISETSTATE == 1) {
115  // Thumb mode
116  const uint32_t ITSTATE = Bits32(cpsr, 15, 10) << 2 | Bits32(cpsr, 26, 25);
117  if (ITSTATE != 0) {
118  const uint32_t condition = Bits32(ITSTATE, 7, 4);
119  if (!ARMConditionPassed(condition, cpsr)) {
120  // We ARE stopped in a Thumb IT instruction on an instruction whose
121  // condition doesn't pass so this instruction won't get executed.
122  // Regardless of why it stopped, we need to clear the stop info
123  thread.SetStopInfo(StopInfoSP());
124  }
125  }
126  }
127 }
128 
130  AddressClass addr_class) const {
131  bool is_alternate_isa = false;
132 
133  switch (addr_class) {
134  case AddressClass::eData:
136  return LLDB_INVALID_ADDRESS;
138  is_alternate_isa = true;
139  break;
140  default: break;
141  }
142 
143  if ((code_addr & 2u) || is_alternate_isa)
144  return code_addr | 1u;
145  return code_addr;
146 }
147 
149  AddressClass addr_class) const {
150  switch (addr_class) {
151  case AddressClass::eData:
153  return LLDB_INVALID_ADDRESS;
154  default: break;
155  }
156  return opcode_addr & ~(1ull);
157 }
Enumerations for broadcasting.
Definition: SBLaunchInfo.h:14
static ConstString GetPluginNameStatic()
static bool RegisterPlugin(ConstString name, const char *description, ABICreateInstance create_callback)
An architecture specification class.
Definition: ArchSpec.h:32
static uint32_t Bit32(const uint32_t bits, const uint32_t bit)
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.
ConstString GetPluginName() override
#define UINT32_MAX
Definition: lldb-defines.h:31
#define LLDB_INVALID_ADDRESS
Invalid value definitions.
Definition: lldb-defines.h:85
uint32_t GetPluginVersion() override
void SetStopInfo(const lldb::StopInfoSP &stop_info_sp)
Definition: Thread.cpp:477
virtual lldb::RegisterContextSP GetRegisterContext()=0
void OverrideStopInfo(Thread &thread) const override
This is currently intended to handle cases where a program stops at an instruction that won&#39;t get exe...
lldb::addr_t GetOpcodeLoadAddress(lldb::addr_t load_addr, AddressClass addr_class) const override
Get load_addr as an opcode for this target.
lldb::ProcessSP GetProcess() const
Definition: Thread.h:154
uint64_t addr_t
Definition: lldb-types.h:83
static bool UnregisterPlugin(ABICreateInstance create_callback)
A uniqued constant string class.
Definition: ConstString.h:38
Definition: SBAddress.h:15
#define UINT64_MAX
Definition: lldb-defines.h:35
static uint32_t Bits32(const uint32_t bits, const uint32_t msbit, const uint32_t lsbit)
static bool ARMConditionPassed(const uint32_t condition, const uint32_t cpsr)
Definition: ARMDefines.h:106
llvm::Triple::ArchType GetMachine() const
Returns a machine family for the current architecture.
Definition: ArchSpec.cpp:726
An error handling class.
Definition: Status.h:44