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//===-- ArchitectureArm.cpp -------------------------------------*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "Plugins/Architecture/Arm/ArchitectureArm.h"
#include "Plugins/Process/Utility/ARMDefines.h"
#include "Plugins/Process/Utility/InstructionUtils.h"
#include "lldb/Core/PluginManager.h"
#include "lldb/Target/RegisterContext.h"
#include "lldb/Target/Thread.h"
#include "lldb/Utility/ArchSpec.h"
using namespace lldb_private;
using namespace lldb;
ConstString ArchitectureArm::GetPluginNameStatic() {
return ConstString("arm");
}
void ArchitectureArm::Initialize() {
PluginManager::RegisterPlugin(GetPluginNameStatic(),
"Arm-specific algorithms",
&ArchitectureArm::Create);
}
void ArchitectureArm::Terminate() {
PluginManager::UnregisterPlugin(&ArchitectureArm::Create);
}
std::unique_ptr<Architecture> ArchitectureArm::Create(const ArchSpec &arch) {
if (arch.GetMachine() != llvm::Triple::arm)
return nullptr;
return std::unique_ptr<Architecture>(new ArchitectureArm());
}
ConstString ArchitectureArm::GetPluginName() { return GetPluginNameStatic(); }
uint32_t ArchitectureArm::GetPluginVersion() { return 1; }
void ArchitectureArm::OverrideStopInfo(Thread &thread) {
// We need to check if we are stopped in Thumb mode in a IT instruction
// and detect if the condition doesn't pass. If this is the case it means
// we won't actually execute this instruction. If this happens we need to
// clear the stop reason to no thread plans think we are stopped for a
// reason and the plans should keep going.
//
// We do this because when single stepping many ARM processes, debuggers
// often use the BVR/BCR registers that says "stop when the PC is not
// equal to its current value". This method of stepping means we can end
// up stopping on instructions inside an if/then block that wouldn't get
// executed. By fixing this we can stop the debugger from seeming like
// you stepped through both the "if" _and_ the "else" clause when source
// level stepping because the debugger stops regardless due to the BVR/BCR
// triggering a stop.
//
// It also means we can set breakpoints on instructions inside an an
// if/then block and correctly skip them if we use the BKPT instruction.
// The ARM and Thumb BKPT instructions are unconditional even when executed
// in a Thumb IT block.
//
// If your debugger inserts software traps in ARM/Thumb code, it will
// need to use 16 and 32 bit instruction for 16 and 32 bit thumb
// instructions respectively. If your debugger inserts a 16 bit thumb
// trap on top of a 32 bit thumb instruction for an opcode that is inside
// an if/then, it will change the it/then to conditionally execute your
// 16 bit trap and then cause your program to crash if it executes the
// trailing 16 bits (the second half of the 32 bit thumb instruction you
// partially overwrote).
RegisterContextSP reg_ctx_sp(thread.GetRegisterContext());
if (!reg_ctx_sp)
return;
const uint32_t cpsr = reg_ctx_sp->GetFlags(0);
if (cpsr == 0)
return;
// Read the J and T bits to get the ISETSTATE
const uint32_t J = Bit32(cpsr, 24);
const uint32_t T = Bit32(cpsr, 5);
const uint32_t ISETSTATE = J << 1 | T;
if (ISETSTATE == 0) {
// NOTE: I am pretty sure we want to enable the code below
// that detects when we stop on an instruction in ARM mode
// that is conditional and the condition doesn't pass. This
// can happen if you set a breakpoint on an instruction that
// is conditional. We currently will _always_ stop on the
// instruction which is bad. You can also run into this while
// single stepping and you could appear to run code in the "if"
// and in the "else" clause because it would stop at all of the
// conditional instructions in both.
// In such cases, we really don't want to stop at this location.
// I will check with the lldb-dev list first before I enable this.
#if 0
// ARM mode: check for condition on intsruction
const addr_t pc = reg_ctx_sp->GetPC();
Status error;
// If we fail to read the opcode we will get UINT64_MAX as the
// result in "opcode" which we can use to detect if we read a
// valid opcode.
const uint64_t opcode = thread.GetProcess()->ReadUnsignedIntegerFromMemory(pc, 4, UINT64_MAX, error);
if (opcode <= UINT32_MAX)
{
const uint32_t condition = Bits32((uint32_t)opcode, 31, 28);
if (!ARMConditionPassed(condition, cpsr))
{
// We ARE stopped on an ARM instruction whose condition doesn't
// pass so this instruction won't get executed.
// Regardless of why it stopped, we need to clear the stop info
thread.SetStopInfo (StopInfoSP());
}
}
#endif
} else if (ISETSTATE == 1) {
// Thumb mode
const uint32_t ITSTATE = Bits32(cpsr, 15, 10) << 2 | Bits32(cpsr, 26, 25);
if (ITSTATE != 0) {
const uint32_t condition = Bits32(ITSTATE, 7, 4);
if (!ARMConditionPassed(condition, cpsr)) {
// We ARE stopped in a Thumb IT instruction on an instruction whose
// condition doesn't pass so this instruction won't get executed.
// Regardless of why it stopped, we need to clear the stop info
thread.SetStopInfo(StopInfoSP());
}
}
}
}
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