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Fix handling of the arm IT instruction in the unwinder
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The IT instruction can specify condition code for up to 4 consecutive
instruction and it is used quite often by clang in epilogues causing
an issue when trying to unwind from locations covered by the IT
instruction and for locatins inmediately after the IT instruction.

Changes made to fix it:
* Introduce the concept of conditional instruction block what is a list
  of consecutive instructions with the same condition. We update the
  unwind information during the conditional instruction block and when
  we reach the end of it (first instruction with a differemt condition)
  then we restore the unwind information we had before the condition.
* Fix a bug in the ARM instruction emulator where neither PC nor the
  ITSTATE was advanced when we reached an instruction what we can't
  decode.

After the change we have no regression on android-arm running the
regular test suit and TestStandardUnwind also passes when running it
with clang as the compiler (previously it failed on an IT instruction).

Differential revision: http://reviews.llvm.org/D16814

llvm-svn: 260368
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Tamas Berghammer committed Feb 10, 2016
1 parent 1b6dacb commit 10e9923
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Showing 6 changed files with 101 additions and 64 deletions.
9 changes: 7 additions & 2 deletions lldb/include/lldb/Core/EmulateInstruction.h
View file
Expand Up @@ -384,6 +384,11 @@ class EmulateInstruction :
const RegisterInfo *reg_info,
const RegisterValue &reg_value);

// Type to represent the condition of an instruction. The UINT32 value is reserved for the
// unconditional case and all other value can be used in an architecture dependent way.
typedef uint32_t InstructionCondition;
static const InstructionCondition UnconditionalCondition = UINT32_MAX;

EmulateInstruction (const ArchSpec &arch);

~EmulateInstruction() override = default;
Expand All @@ -403,8 +408,8 @@ class EmulateInstruction :
virtual bool
EvaluateInstruction (uint32_t evaluate_options) = 0;

virtual bool
IsInstructionConditional() { return false; }
virtual InstructionCondition
GetInstructionCondition() { return UnconditionalCondition; }

virtual bool
TestEmulation (Stream *out_stream, ArchSpec &arch, OptionValueDictionary *test_data) = 0;
Expand Down
2 changes: 1 addition & 1 deletion lldb/include/lldb/Symbol/UnwindPlan.h
View file
Expand Up @@ -539,7 +539,7 @@ class UnwindPlan {
AppendRow (const RowSP& row_sp);

void
InsertRow (const RowSP& row_sp);
InsertRow (const RowSP& row_sp, bool replace_existing = false);

// Returns a pointer to the best row for the given offset into the function's instructions.
// If offset is -1 it indicates that the function start is unknown - the final row in the UnwindPlan is returned.
Expand Down
38 changes: 18 additions & 20 deletions lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.cpp
View file
Expand Up @@ -13587,10 +13587,7 @@ EmulateInstructionARM::EvaluateInstruction (uint32_t evaluate_options)
opcode_data = GetThumbOpcodeForInstruction (m_opcode.GetOpcode32(), m_arm_isa);
else if (m_opcode_mode == eModeARM)
opcode_data = GetARMOpcodeForInstruction (m_opcode.GetOpcode32(), m_arm_isa);

if (opcode_data == NULL)
return false;


const bool auto_advance_pc = evaluate_options & eEmulateInstructionOptionAutoAdvancePC;
m_ignore_conditions = evaluate_options & eEmulateInstructionOptionIgnoreConditions;

Expand All @@ -13614,47 +13611,48 @@ EmulateInstructionARM::EvaluateInstruction (uint32_t evaluate_options)
if (!success)
return false;
}

// Call the Emulate... function.
success = (this->*opcode_data->callback) (m_opcode.GetOpcode32(), opcode_data->encoding);
if (!success)
return false;

// Call the Emulate... function if we managed to decode the opcode.
if (opcode_data)
{
success = (this->*opcode_data->callback) (m_opcode.GetOpcode32(), opcode_data->encoding);
if (!success)
return false;
}

// Advance the ITSTATE bits to their values for the next instruction if we haven't just executed
// an IT instruction what initialized it.
if (m_opcode_mode == eModeThumb && m_it_session.InITBlock() &&
opcode_data->callback != &EmulateInstructionARM::EmulateIT)
(opcode_data == nullptr || opcode_data->callback != &EmulateInstructionARM::EmulateIT))
m_it_session.ITAdvance();

if (auto_advance_pc)
{
uint32_t after_pc_value = ReadRegisterUnsigned (eRegisterKindDWARF, dwarf_pc, 0, &success);
if (!success)
return false;

if (auto_advance_pc && (after_pc_value == orig_pc_value))
{
if (opcode_data->size == eSize32)
after_pc_value += 4;
else if (opcode_data->size == eSize16)
after_pc_value += 2;

after_pc_value += m_opcode.GetByteSize();

EmulateInstruction::Context context;
context.type = eContextAdvancePC;
context.SetNoArgs();
if (!WriteRegisterUnsigned (context, eRegisterKindDWARF, dwarf_pc, after_pc_value))
return false;

}
}
return true;
}

bool
EmulateInstructionARM::IsInstructionConditional()
EmulateInstruction::InstructionCondition
EmulateInstructionARM::GetInstructionCondition()
{
const uint32_t cond = CurrentCond (m_opcode.GetOpcode32());
return cond != 0xe && cond != 0xf && cond != UINT32_MAX;
if (cond == 0xe || cond == 0xf || cond == UINT32_MAX)
return EmulateInstruction::UnconditionalCondition;
return cond;
}

bool
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4 changes: 2 additions & 2 deletions lldb/source/Plugins/Instruction/ARM/EmulateInstructionARM.h
View file
Expand Up @@ -166,8 +166,8 @@ class EmulateInstructionARM : public EmulateInstruction
bool
EvaluateInstruction (uint32_t evaluate_options) override;

bool
IsInstructionConditional() override;
InstructionCondition
GetInstructionCondition() override;

bool
TestEmulation (Stream *out_stream, ArchSpec &arch, OptionValueDictionary *test_data) override;
Expand Down
108 changes: 70 additions & 38 deletions lldb/source/Plugins/UnwindAssembly/InstEmulation/UnwindAssemblyInstEmulation.cpp
View file
Expand Up @@ -125,6 +125,10 @@ UnwindAssemblyInstEmulation::GetNonCallSiteUnwindPlanFromAssembly (AddressRange&
RegisterInfo ra_reg_info;
m_inst_emulator_ap->GetRegisterInfo (eRegisterKindGeneric, LLDB_REGNUM_GENERIC_RA, ra_reg_info);

// The architecture dependent condition code of the last processed instruction.
EmulateInstruction::InstructionCondition last_condition = EmulateInstruction::UnconditionalCondition;
lldb::addr_t condition_block_start_offset = 0;

for (size_t idx=0; idx<num_instructions; ++idx)
{
m_curr_row_modified = false;
Expand All @@ -146,7 +150,41 @@ UnwindAssemblyInstEmulation::GetNonCallSiteUnwindPlanFromAssembly (AddressRange&
UnwindPlan::Row *newrow = new UnwindPlan::Row;
*newrow = *it->second.first;
m_curr_row.reset(newrow);
m_register_values = it->second.second;;
m_register_values = it->second.second;
}

m_inst_emulator_ap->SetInstruction (inst->GetOpcode(),
inst->GetAddress(),
exe_ctx.GetTargetPtr());

if (last_condition != m_inst_emulator_ap->GetInstructionCondition())
{
if (m_inst_emulator_ap->GetInstructionCondition() != EmulateInstruction::UnconditionalCondition &&
saved_unwind_states.count(current_offset) == 0)
{
// If we don't have a saved row for the current offset then save our
// current state because we will have to restore it after the
// conditional block.
auto new_row = std::make_shared<UnwindPlan::Row>(*m_curr_row.get());
saved_unwind_states.insert({current_offset, {new_row, m_register_values}});
}

// If the last instruction was conditional with a different condition
// then the then current condition then restore the condition.
if (last_condition != EmulateInstruction::UnconditionalCondition)
{
const auto& saved_state = saved_unwind_states.at(condition_block_start_offset);
m_curr_row = std::make_shared<UnwindPlan::Row>(*saved_state.first);
m_curr_row->SetOffset(current_offset);
m_register_values = saved_state.second;
bool replace_existing = true; // The last instruction might already
// created a row for this offset and
// we want to overwrite it.
unwind_plan.InsertRow(std::make_shared<UnwindPlan::Row>(*m_curr_row), replace_existing);
}

// We are starting a new conditional block at the catual offset
condition_block_start_offset = current_offset;
}

if (log && log->GetVerbose ())
Expand All @@ -158,9 +196,7 @@ UnwindAssemblyInstEmulation::GetNonCallSiteUnwindPlanFromAssembly (AddressRange&
log->PutCString (strm.GetData());
}

m_inst_emulator_ap->SetInstruction (inst->GetOpcode(),
inst->GetAddress(),
exe_ctx.GetTargetPtr());
last_condition = m_inst_emulator_ap->GetInstructionCondition();

m_inst_emulator_ap->EvaluateInstruction (eEmulateInstructionOptionIgnoreConditions);

Expand Down Expand Up @@ -503,8 +539,7 @@ UnwindAssemblyInstEmulation::WriteRegister (EmulateInstruction *instruction,
log->PutCString(strm.GetData());
}

if (!instruction->IsInstructionConditional())
SetRegisterValue (*reg_info, reg_value);
SetRegisterValue (*reg_info, reg_value);

switch (context.type)
{
Expand Down Expand Up @@ -566,45 +601,42 @@ UnwindAssemblyInstEmulation::WriteRegister (EmulateInstruction *instruction,

case EmulateInstruction::eContextPopRegisterOffStack:
{
if (!instruction->IsInstructionConditional())
const uint32_t reg_num = reg_info->kinds[m_unwind_plan_ptr->GetRegisterKind()];
const uint32_t generic_regnum = reg_info->kinds[eRegisterKindGeneric];
if (reg_num != LLDB_INVALID_REGNUM && generic_regnum != LLDB_REGNUM_GENERIC_SP)
{
const uint32_t reg_num = reg_info->kinds[m_unwind_plan_ptr->GetRegisterKind()];
const uint32_t generic_regnum = reg_info->kinds[eRegisterKindGeneric];
if (reg_num != LLDB_INVALID_REGNUM && generic_regnum != LLDB_REGNUM_GENERIC_SP)
switch (context.info_type)
{
switch (context.info_type)
{
case EmulateInstruction::eInfoTypeAddress:
if (m_pushed_regs.find(reg_num) != m_pushed_regs.end() &&
context.info.address == m_pushed_regs[reg_num])
{
m_curr_row->SetRegisterLocationToSame(reg_num,
false /*must_replace*/);
m_curr_row_modified = true;
}
break;
case EmulateInstruction::eInfoTypeISA:
assert((generic_regnum == LLDB_REGNUM_GENERIC_PC ||
generic_regnum == LLDB_REGNUM_GENERIC_FLAGS) &&
"eInfoTypeISA used for poping a register other the the PC/FLAGS");
if (generic_regnum != LLDB_REGNUM_GENERIC_FLAGS)
{
m_curr_row->SetRegisterLocationToSame(reg_num,
false /*must_replace*/);
m_curr_row_modified = true;
}
break;
default:
assert(false && "unhandled case, add code to handle this!");
break;
}
case EmulateInstruction::eInfoTypeAddress:
if (m_pushed_regs.find(reg_num) != m_pushed_regs.end() &&
context.info.address == m_pushed_regs[reg_num])
{
m_curr_row->SetRegisterLocationToSame(reg_num,
false /*must_replace*/);
m_curr_row_modified = true;
}
break;
case EmulateInstruction::eInfoTypeISA:
assert((generic_regnum == LLDB_REGNUM_GENERIC_PC ||
generic_regnum == LLDB_REGNUM_GENERIC_FLAGS) &&
"eInfoTypeISA used for poping a register other the the PC/FLAGS");
if (generic_regnum != LLDB_REGNUM_GENERIC_FLAGS)
{
m_curr_row->SetRegisterLocationToSame(reg_num,
false /*must_replace*/);
m_curr_row_modified = true;
}
break;
default:
assert(false && "unhandled case, add code to handle this!");
break;
}
}
}
break;

case EmulateInstruction::eContextSetFramePointer:
if (!m_fp_is_cfa && !instruction->IsInstructionConditional())
if (!m_fp_is_cfa)
{
m_fp_is_cfa = true;
m_cfa_reg_info = *reg_info;
Expand All @@ -619,7 +651,7 @@ UnwindAssemblyInstEmulation::WriteRegister (EmulateInstruction *instruction,
case EmulateInstruction::eContextAdjustStackPointer:
// If we have created a frame using the frame pointer, don't follow
// subsequent adjustments to the stack pointer.
if (!m_fp_is_cfa && !instruction->IsInstructionConditional())
if (!m_fp_is_cfa)
{
m_curr_row->GetCFAValue().SetIsRegisterPlusOffset(
m_curr_row->GetCFAValue().GetRegisterNumber(),
Expand Down
4 changes: 3 additions & 1 deletion lldb/source/Symbol/UnwindPlan.cpp
View file
Expand Up @@ -338,7 +338,7 @@ UnwindPlan::AppendRow (const UnwindPlan::RowSP &row_sp)
}

void
UnwindPlan::InsertRow (const UnwindPlan::RowSP &row_sp)
UnwindPlan::InsertRow (const UnwindPlan::RowSP &row_sp, bool replace_existing)
{
collection::iterator it = m_row_list.begin();
while (it != m_row_list.end()) {
Expand All @@ -349,6 +349,8 @@ UnwindPlan::InsertRow (const UnwindPlan::RowSP &row_sp)
}
if (it == m_row_list.end() || (*it)->GetOffset() != row_sp->GetOffset())
m_row_list.insert(it, row_sp);
else if (replace_existing)
*it = row_sp;
}

UnwindPlan::RowSP
Expand Down

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