src/developer/debug/debug_agent/debug_registers_x64.cc - fuchsia - Git at Google

 // Copyright 2020 The Fuchsia Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include <lib/syslog/cpp/macros.h>
 #include <zircon/hw/debug/x86.h>

 #include "src/developer/debug/debug_agent/align.h"
 #include "src/developer/debug/debug_agent/debug_registers.h"
 #include "src/developer/debug/shared/arch_x86.h"
 #include "src/lib/fxl/strings/string_printf.h"

 namespace debug_agent {

 namespace {

 uint64_t HWDebugResourceEnabled(uint64_t dr7, size_t index) {
   FX_DCHECK(index < 4);

   // clang-format off
   static uint64_t masks[4] = { X86_FLAG_MASK(DR7L0),
                                X86_FLAG_MASK(DR7L1),
                                X86_FLAG_MASK(DR7L2),
                                X86_FLAG_MASK(DR7L3)};
   // clang-format on

   return (dr7 & masks[index]) != 0;
 }

 // A watchpoint is configured by DR7RW<i> = 0b10 (write) or 0b11 (read/write).
 bool IsWatchpoint(uint64_t dr7, size_t index) {
   // clang-format off
   switch (index) {
     case 0: return (X86_FLAG_VALUE(dr7, DR7RW0) & 1) > 0;
     case 1: return (X86_FLAG_VALUE(dr7, DR7RW1) & 1) > 0;
     case 2: return (X86_FLAG_VALUE(dr7, DR7RW2) & 1) > 0;
     case 3: return (X86_FLAG_VALUE(dr7, DR7RW3) & 1) > 0;
   }
   // clang-format on

   FX_NOTREACHED();
   return false;
 }

 uint64_t WatchpointAddressAlign(const debug_ipc::AddressRange& range) {
   // clang-format off
   switch (range.size()) {
     case 1: return range.begin();
     case 2: return range.begin() & (uint64_t)(~0b1);
     case 4: return range.begin() & (uint64_t)(~0b11);
     case 8: return range.begin() & (uint64_t)(~0b111);
   }
   // clang-format on

   return 0;
 }

 uint64_t X86LenToLength(uint64_t len) {
   // clang-format off
   switch (len) {
     case 0: return 1;
     case 1: return 2;
     case 2: return 8;
     case 3: return 4;
   }
   // clang-format on

   FX_NOTREACHED() << "Invalid len: " << len;
   return 0;
 }

 uint64_t LengthToX86Length(uint64_t len) {
   // clang-format off
   switch (len) {
     case 1: return 0;
     case 2: return 1;
     case 8: return 2;
     case 4: return 3;
   }
   // clang-format on

   FX_NOTREACHED() << "Invalid len: " << len;
   return 0;
 }

 void SetWatchpointFlags(uint64_t* dr7, int slot, bool active, uint64_t size,
                         debug_ipc::BreakpointType type) {
   uint32_t rw_value = 0;
   if (type == debug_ipc::BreakpointType::kWrite) {
     rw_value = 0b1;
   } else if (type == debug_ipc::BreakpointType::kReadWrite) {
     rw_value = 0b11;
   }

   // clang-format off
   switch (slot) {
     case 0: {
       X86_DBG_CONTROL_L0_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW0_SET(dr7, rw_value);
       X86_DBG_CONTROL_LEN0_SET(dr7, size ? LengthToX86Length(size) : 0);
       return;
     }
     case 1: {
       X86_DBG_CONTROL_L1_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW1_SET(dr7, rw_value);
       X86_DBG_CONTROL_LEN1_SET(dr7, size ? LengthToX86Length(size) : 0);
       return;
     }
     case 2: {
       X86_DBG_CONTROL_L2_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW2_SET(dr7, rw_value);
       X86_DBG_CONTROL_LEN2_SET(dr7, size ? LengthToX86Length(size) : 0);
       return;
     }
     case 3: {
       X86_DBG_CONTROL_L3_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW3_SET(dr7, rw_value);
       X86_DBG_CONTROL_LEN3_SET(dr7, size ? LengthToX86Length(size) : 0);
       return;
     }
   }
   // clang-format on

   FX_NOTREACHED() << "Invalid slot: " << slot;
 }

 // x86 uses the following bits to represent watchpoint lenghts:
 //   00: 1 byte.
 //   10: 2 bytes.
 //   11: 8 bytes.
 //   10: 4 bytes.
 uint64_t GetWatchpointLength(uint64_t dr7, int slot) {
   // clang-format off
   switch (slot) {
     case 0: return X86LenToLength(X86_DBG_CONTROL_LEN0_GET(dr7));
     case 1: return X86LenToLength(X86_DBG_CONTROL_LEN1_GET(dr7));
     case 2: return X86LenToLength(X86_DBG_CONTROL_LEN2_GET(dr7));
     case 3: return X86LenToLength(X86_DBG_CONTROL_LEN3_GET(dr7));
   }
   // clang-format on

   FX_NOTREACHED() << "Invalid slot: " << slot;
   return -1;
 }

 void SetHWBreakpointFlags(uint64_t* dr7, int slot, bool active) {
   switch (slot) {
     case 0: {
       X86_DBG_CONTROL_L0_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW0_SET(dr7, 0);
       X86_DBG_CONTROL_LEN0_SET(dr7, 0);
       return;
     }
     case 1: {
       X86_DBG_CONTROL_L1_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW1_SET(dr7, 0);
       X86_DBG_CONTROL_LEN1_SET(dr7, 0);
       return;
     }
     case 2: {
       X86_DBG_CONTROL_L2_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW2_SET(dr7, 0);
       X86_DBG_CONTROL_LEN2_SET(dr7, 0);
       return;
     }
     case 3: {
       X86_DBG_CONTROL_L3_SET(dr7, active ? 1 : 0);
       X86_DBG_CONTROL_RW3_SET(dr7, 0);
       X86_DBG_CONTROL_LEN3_SET(dr7, 0);
       return;
     }
   }

   FX_NOTREACHED() << "Invalid slot: " << slot;
 }

 std::string DR6ToString(uint64_t dr6) {
   return fxl::StringPrintf(
       "0x%lx: B0=%d, B1=%d, B2=%d, B3=%d, BD=%d, BS=%d, BT=%d", dr6, X86_FLAG_VALUE(dr6, DR6B0),
       X86_FLAG_VALUE(dr6, DR6B1), X86_FLAG_VALUE(dr6, DR6B2), X86_FLAG_VALUE(dr6, DR6B3),
       X86_FLAG_VALUE(dr6, DR6BD), X86_FLAG_VALUE(dr6, DR6BS), X86_FLAG_VALUE(dr6, DR6BT));
 }

 std::string DR7ToString(uint64_t dr7) {
   return fxl::StringPrintf(
       "0x%lx: L0=%d, G0=%d, L1=%d, G1=%d, L2=%d, G2=%d, L3=%d, G4=%d, LE=%d, "
       "GE=%d, GD=%d, R/W0=%d, LEN0=%d, R/W1=%d, LEN1=%d, R/W2=%d, LEN2=%d, "
       "R/W3=%d, LEN3=%d",
       dr7, X86_FLAG_VALUE(dr7, DR7L0), X86_FLAG_VALUE(dr7, DR7G0), X86_FLAG_VALUE(dr7, DR7L1),
       X86_FLAG_VALUE(dr7, DR7G1), X86_FLAG_VALUE(dr7, DR7L2), X86_FLAG_VALUE(dr7, DR7G2),
       X86_FLAG_VALUE(dr7, DR7L3), X86_FLAG_VALUE(dr7, DR7G3), X86_FLAG_VALUE(dr7, DR7LE),
       X86_FLAG_VALUE(dr7, DR7GE), X86_FLAG_VALUE(dr7, DR7GD), X86_FLAG_VALUE(dr7, DR7RW0),
       X86_FLAG_VALUE(dr7, DR7LEN0), X86_FLAG_VALUE(dr7, DR7RW1), X86_FLAG_VALUE(dr7, DR7LEN1),
       X86_FLAG_VALUE(dr7, DR7RW2), X86_FLAG_VALUE(dr7, DR7LEN2), X86_FLAG_VALUE(dr7, DR7RW3),
       X86_FLAG_VALUE(dr7, DR7LEN3));
 }

 }  // namespace

 bool DebugRegisters::SetHWBreakpoint(uint64_t address) {
   // Search for a free slot.
   int slot = -1;
   for (size_t i = 0; i < 4; i++) {
     if (HWDebugResourceEnabled(regs_.dr7, i)) {
       // If it's already bound there, we don't need to do anything.
       if (regs_.dr[i] == address)
         return false;
     } else {
       slot = i;
       break;
     }
   }

   if (slot == -1)
     return false;

   // We found a slot, we bind the address.
   regs_.dr[slot] = address;
   SetHWBreakpointFlags(&regs_.dr7, slot, true);
   return true;
 }

 bool DebugRegisters::RemoveHWBreakpoint(uint64_t address) {
   // Search for the slot.
   for (int i = 0; i < 4; i++) {
     if (!HWDebugResourceEnabled(regs_.dr7, i) || IsWatchpoint(regs_.dr7, i))
       continue;

     if (regs_.dr[i] != address)
       continue;

     // Clear this breakpoint.
     regs_.dr[i] = 0;
     SetHWBreakpointFlags(&regs_.dr7, i, false);

     return true;
   }

   // We didn't find the address.
   return false;
 }

 // On x64, watchpoint_count is unnecessary for this computation.
 std::optional<WatchpointInfo> DebugRegisters::SetWatchpoint(debug_ipc::BreakpointType type,
                                                             const debug_ipc::AddressRange& range,
                                                             uint32_t watchpoint_count) {
   if (!debug_ipc::IsWatchpointType(type))
     return std::nullopt;

   // Create an aligned range that will cover the watchpoint.
   auto aligned_range = AlignRange(range);
   if (!aligned_range.has_value())
     return std::nullopt;

   uint64_t address = aligned_range->begin();
   uint64_t size = aligned_range->end() - aligned_range->begin();

   // Search for a free slot.
   int slot = -1;
   for (int i = 0; i < 4; i++) {
     if (HWDebugResourceEnabled(regs_.dr7, i)) {
       // If it's the same address, we don't need to do anything.
       // For watchpoints, we need to compare against the range.
       if ((regs_.dr[i] == address) && GetWatchpointLength(regs_.dr7, i) == size)
         return std::nullopt;
     } else {
       slot = i;
       break;
     }
   }

   if (slot == -1)
     return std::nullopt;

   // We found a slot, we bind the watchpoint.
   regs_.dr[slot] = address;
   SetWatchpointFlags(&regs_.dr7, slot, true, size, type);

   return WatchpointInfo(aligned_range.value(), slot);
 }

 // On x64, watchpoint_count is unnecessary for this computation.
 bool DebugRegisters::RemoveWatchpoint(const debug_ipc::AddressRange& range,
                                       uint32_t watchpoint_count) {
   uint64_t aligned_address = WatchpointAddressAlign(range);
   if (!aligned_address)
     return false;

   for (int slot = 0; slot < 4; slot++) {
     if (!IsWatchpoint(regs_.dr7, slot))
       continue;

     // Both address and length should match.
     if ((regs_.dr[slot] != aligned_address) ||
         GetWatchpointLength(regs_.dr7, slot) != range.size()) {
       continue;
     }

     // Clear this breakpoint.
     regs_.dr[slot] = 0;
     SetWatchpointFlags(&regs_.dr7, slot, false, 0, debug_ipc::BreakpointType::kLast);
     return true;
   }

   // We didn't find the address.
   return false;
 }

 std::optional<WatchpointInfo> DebugRegisters::DecodeHitWatchpoint() const {
   uint64_t addr = 0;
   uint64_t length = 0;
   int slot = 0;
   if (X86_FLAG_VALUE(regs_.dr6, DR6B0)) {
     addr = regs_.dr[0];
     length = GetWatchpointLength(regs_.dr7, 0);
     slot = 0;
   } else if (X86_FLAG_VALUE(regs_.dr6, DR6B1)) {
     addr = regs_.dr[1];
     length = GetWatchpointLength(regs_.dr7, 1);
     slot = 1;
   } else if (X86_FLAG_VALUE(regs_.dr6, DR6B2)) {
     addr = regs_.dr[2];
     length = GetWatchpointLength(regs_.dr7, 2);
     slot = 2;
   } else if (X86_FLAG_VALUE(regs_.dr6, DR6B3)) {
     addr = regs_.dr[3];
     length = GetWatchpointLength(regs_.dr7, 3);
     slot = 3;
   } else {
     FX_NOTREACHED() << "x86: No known hw exception set in DR6";
     return std::nullopt;
   }

   return WatchpointInfo({addr, addr + length}, slot);
 }

 void DebugRegisters::SetForHitWatchpoint(int slot) {
   switch (slot) {
     case 0:
       regs_.dr6 |= X86_FLAG_MASK(DR6B0);
       break;
     case 1:
       regs_.dr6 |= X86_FLAG_MASK(DR6B1);
       break;
     case 2:
       regs_.dr6 |= X86_FLAG_MASK(DR6B2);
       break;
     case 3:
       regs_.dr6 |= X86_FLAG_MASK(DR6B3);
       break;
     default:
       FX_NOTREACHED() << "Bad slot.";
       break;
   }
 }

 std::string DebugRegisters::ToString() const {
   std::stringstream ss;
   ss << "Regs: " << std::endl
      << "DR0: 0x" << std::hex << regs_.dr[0] << std::endl
      << "DR1: 0x" << std::hex << regs_.dr[1] << std::endl
      << "DR2: 0x" << std::hex << regs_.dr[2] << std::endl
      << "DR3: 0x" << std::hex << regs_.dr[3] << std::endl
      << "DR6: " << DR6ToString(regs_.dr6) << std::endl
      << "DR7: " << DR7ToString(regs_.dr7) << std::endl;
   return ss.str();
 }

 }  // namespace debug_agent
	// Copyright 2020 The Fuchsia Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include <lib/syslog/cpp/macros.h>
	#include <zircon/hw/debug/x86.h>

	#include "src/developer/debug/debug_agent/align.h"
	#include "src/developer/debug/debug_agent/debug_registers.h"
	#include "src/developer/debug/shared/arch_x86.h"
	#include "src/lib/fxl/strings/string_printf.h"

	namespace debug_agent {

	namespace {

	uint64_t HWDebugResourceEnabled(uint64_t dr7, size_t index) {
	FX_DCHECK(index < 4);

	// clang-format off
	static uint64_t masks[4] = { X86_FLAG_MASK(DR7L0),
	X86_FLAG_MASK(DR7L1),
	X86_FLAG_MASK(DR7L2),
	X86_FLAG_MASK(DR7L3)};
	// clang-format on

	return (dr7 & masks[index]) != 0;
	}

	// A watchpoint is configured by DR7RW<i> = 0b10 (write) or 0b11 (read/write).
	bool IsWatchpoint(uint64_t dr7, size_t index) {
	// clang-format off
	switch (index) {
	case 0: return (X86_FLAG_VALUE(dr7, DR7RW0) & 1) > 0;
	case 1: return (X86_FLAG_VALUE(dr7, DR7RW1) & 1) > 0;
	case 2: return (X86_FLAG_VALUE(dr7, DR7RW2) & 1) > 0;
	case 3: return (X86_FLAG_VALUE(dr7, DR7RW3) & 1) > 0;
	}
	// clang-format on

	FX_NOTREACHED();
	return false;
	}

	uint64_t WatchpointAddressAlign(const debug_ipc::AddressRange& range) {
	// clang-format off
	switch (range.size()) {
	case 1: return range.begin();
	case 2: return range.begin() & (uint64_t)(~0b1);
	case 4: return range.begin() & (uint64_t)(~0b11);
	case 8: return range.begin() & (uint64_t)(~0b111);
	}
	// clang-format on

	return 0;
	}

	uint64_t X86LenToLength(uint64_t len) {
	// clang-format off
	switch (len) {
	case 0: return 1;
	case 1: return 2;
	case 2: return 8;
	case 3: return 4;
	}
	// clang-format on

	FX_NOTREACHED() << "Invalid len: " << len;
	return 0;
	}

	uint64_t LengthToX86Length(uint64_t len) {
	// clang-format off
	switch (len) {
	case 1: return 0;
	case 2: return 1;
	case 8: return 2;
	case 4: return 3;
	}
	// clang-format on

	FX_NOTREACHED() << "Invalid len: " << len;
	return 0;
	}

	void SetWatchpointFlags(uint64_t* dr7, int slot, bool active, uint64_t size,
	debug_ipc::BreakpointType type) {
	uint32_t rw_value = 0;
	if (type == debug_ipc::BreakpointType::kWrite) {
	rw_value = 0b1;
	} else if (type == debug_ipc::BreakpointType::kReadWrite) {
	rw_value = 0b11;
	}

	// clang-format off
	switch (slot) {
	case 0: {
	X86_DBG_CONTROL_L0_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW0_SET(dr7, rw_value);
	X86_DBG_CONTROL_LEN0_SET(dr7, size ? LengthToX86Length(size) : 0);
	return;
	}
	case 1: {
	X86_DBG_CONTROL_L1_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW1_SET(dr7, rw_value);
	X86_DBG_CONTROL_LEN1_SET(dr7, size ? LengthToX86Length(size) : 0);
	return;
	}
	case 2: {
	X86_DBG_CONTROL_L2_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW2_SET(dr7, rw_value);
	X86_DBG_CONTROL_LEN2_SET(dr7, size ? LengthToX86Length(size) : 0);
	return;
	}
	case 3: {
	X86_DBG_CONTROL_L3_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW3_SET(dr7, rw_value);
	X86_DBG_CONTROL_LEN3_SET(dr7, size ? LengthToX86Length(size) : 0);
	return;
	}
	}
	// clang-format on

	FX_NOTREACHED() << "Invalid slot: " << slot;
	}

	// x86 uses the following bits to represent watchpoint lenghts:
	// 00: 1 byte.
	// 10: 2 bytes.
	// 11: 8 bytes.
	// 10: 4 bytes.
	uint64_t GetWatchpointLength(uint64_t dr7, int slot) {
	// clang-format off
	switch (slot) {
	case 0: return X86LenToLength(X86_DBG_CONTROL_LEN0_GET(dr7));
	case 1: return X86LenToLength(X86_DBG_CONTROL_LEN1_GET(dr7));
	case 2: return X86LenToLength(X86_DBG_CONTROL_LEN2_GET(dr7));
	case 3: return X86LenToLength(X86_DBG_CONTROL_LEN3_GET(dr7));
	}
	// clang-format on

	FX_NOTREACHED() << "Invalid slot: " << slot;
	return -1;
	}

	void SetHWBreakpointFlags(uint64_t* dr7, int slot, bool active) {
	switch (slot) {
	case 0: {
	X86_DBG_CONTROL_L0_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW0_SET(dr7, 0);
	X86_DBG_CONTROL_LEN0_SET(dr7, 0);
	return;
	}
	case 1: {
	X86_DBG_CONTROL_L1_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW1_SET(dr7, 0);
	X86_DBG_CONTROL_LEN1_SET(dr7, 0);
	return;
	}
	case 2: {
	X86_DBG_CONTROL_L2_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW2_SET(dr7, 0);
	X86_DBG_CONTROL_LEN2_SET(dr7, 0);
	return;
	}
	case 3: {
	X86_DBG_CONTROL_L3_SET(dr7, active ? 1 : 0);
	X86_DBG_CONTROL_RW3_SET(dr7, 0);
	X86_DBG_CONTROL_LEN3_SET(dr7, 0);
	return;
	}
	}

	FX_NOTREACHED() << "Invalid slot: " << slot;
	}

	std::string DR6ToString(uint64_t dr6) {
	return fxl::StringPrintf(
	"0x%lx: B0=%d, B1=%d, B2=%d, B3=%d, BD=%d, BS=%d, BT=%d", dr6, X86_FLAG_VALUE(dr6, DR6B0),
	X86_FLAG_VALUE(dr6, DR6B1), X86_FLAG_VALUE(dr6, DR6B2), X86_FLAG_VALUE(dr6, DR6B3),
	X86_FLAG_VALUE(dr6, DR6BD), X86_FLAG_VALUE(dr6, DR6BS), X86_FLAG_VALUE(dr6, DR6BT));
	}

	std::string DR7ToString(uint64_t dr7) {
	return fxl::StringPrintf(
	"0x%lx: L0=%d, G0=%d, L1=%d, G1=%d, L2=%d, G2=%d, L3=%d, G4=%d, LE=%d, "
	"GE=%d, GD=%d, R/W0=%d, LEN0=%d, R/W1=%d, LEN1=%d, R/W2=%d, LEN2=%d, "
	"R/W3=%d, LEN3=%d",
	dr7, X86_FLAG_VALUE(dr7, DR7L0), X86_FLAG_VALUE(dr7, DR7G0), X86_FLAG_VALUE(dr7, DR7L1),
	X86_FLAG_VALUE(dr7, DR7G1), X86_FLAG_VALUE(dr7, DR7L2), X86_FLAG_VALUE(dr7, DR7G2),
	X86_FLAG_VALUE(dr7, DR7L3), X86_FLAG_VALUE(dr7, DR7G3), X86_FLAG_VALUE(dr7, DR7LE),
	X86_FLAG_VALUE(dr7, DR7GE), X86_FLAG_VALUE(dr7, DR7GD), X86_FLAG_VALUE(dr7, DR7RW0),
	X86_FLAG_VALUE(dr7, DR7LEN0), X86_FLAG_VALUE(dr7, DR7RW1), X86_FLAG_VALUE(dr7, DR7LEN1),
	X86_FLAG_VALUE(dr7, DR7RW2), X86_FLAG_VALUE(dr7, DR7LEN2), X86_FLAG_VALUE(dr7, DR7RW3),
	X86_FLAG_VALUE(dr7, DR7LEN3));
	}

	} // namespace

	bool DebugRegisters::SetHWBreakpoint(uint64_t address) {
	// Search for a free slot.
	int slot = -1;
	for (size_t i = 0; i < 4; i++) {
	if (HWDebugResourceEnabled(regs_.dr7, i)) {
	// If it's already bound there, we don't need to do anything.
	if (regs_.dr[i] == address)
	return false;
	} else {
	slot = i;
	break;
	}
	}

	if (slot == -1)
	return false;

	// We found a slot, we bind the address.
	regs_.dr[slot] = address;
	SetHWBreakpointFlags(&regs_.dr7, slot, true);
	return true;
	}

	bool DebugRegisters::RemoveHWBreakpoint(uint64_t address) {
	// Search for the slot.
	for (int i = 0; i < 4; i++) {
	if (!HWDebugResourceEnabled(regs_.dr7, i) \|\| IsWatchpoint(regs_.dr7, i))
	continue;

	if (regs_.dr[i] != address)
	continue;

	// Clear this breakpoint.
	regs_.dr[i] = 0;
	SetHWBreakpointFlags(&regs_.dr7, i, false);

	return true;
	}

	// We didn't find the address.
	return false;
	}

	// On x64, watchpoint_count is unnecessary for this computation.
	std::optional<WatchpointInfo> DebugRegisters::SetWatchpoint(debug_ipc::BreakpointType type,
	const debug_ipc::AddressRange& range,
	uint32_t watchpoint_count) {
	if (!debug_ipc::IsWatchpointType(type))
	return std::nullopt;

	// Create an aligned range that will cover the watchpoint.
	auto aligned_range = AlignRange(range);
	if (!aligned_range.has_value())
	return std::nullopt;

	uint64_t address = aligned_range->begin();
	uint64_t size = aligned_range->end() - aligned_range->begin();

	// Search for a free slot.
	int slot = -1;
	for (int i = 0; i < 4; i++) {
	if (HWDebugResourceEnabled(regs_.dr7, i)) {
	// If it's the same address, we don't need to do anything.
	// For watchpoints, we need to compare against the range.
	if ((regs_.dr[i] == address) && GetWatchpointLength(regs_.dr7, i) == size)
	return std::nullopt;
	} else {
	slot = i;
	break;
	}
	}

	if (slot == -1)
	return std::nullopt;

	// We found a slot, we bind the watchpoint.
	regs_.dr[slot] = address;
	SetWatchpointFlags(&regs_.dr7, slot, true, size, type);

	return WatchpointInfo(aligned_range.value(), slot);
	}

	// On x64, watchpoint_count is unnecessary for this computation.
	bool DebugRegisters::RemoveWatchpoint(const debug_ipc::AddressRange& range,
	uint32_t watchpoint_count) {
	uint64_t aligned_address = WatchpointAddressAlign(range);
	if (!aligned_address)
	return false;

	for (int slot = 0; slot < 4; slot++) {
	if (!IsWatchpoint(regs_.dr7, slot))
	continue;

	// Both address and length should match.
	if ((regs_.dr[slot] != aligned_address) \|\|
	GetWatchpointLength(regs_.dr7, slot) != range.size()) {
	continue;
	}

	// Clear this breakpoint.
	regs_.dr[slot] = 0;
	SetWatchpointFlags(&regs_.dr7, slot, false, 0, debug_ipc::BreakpointType::kLast);
	return true;
	}

	// We didn't find the address.
	return false;
	}

	std::optional<WatchpointInfo> DebugRegisters::DecodeHitWatchpoint() const {
	uint64_t addr = 0;
	uint64_t length = 0;
	int slot = 0;
	if (X86_FLAG_VALUE(regs_.dr6, DR6B0)) {
	addr = regs_.dr[0];
	length = GetWatchpointLength(regs_.dr7, 0);
	slot = 0;
	} else if (X86_FLAG_VALUE(regs_.dr6, DR6B1)) {
	addr = regs_.dr[1];
	length = GetWatchpointLength(regs_.dr7, 1);
	slot = 1;
	} else if (X86_FLAG_VALUE(regs_.dr6, DR6B2)) {
	addr = regs_.dr[2];
	length = GetWatchpointLength(regs_.dr7, 2);
	slot = 2;
	} else if (X86_FLAG_VALUE(regs_.dr6, DR6B3)) {
	addr = regs_.dr[3];
	length = GetWatchpointLength(regs_.dr7, 3);
	slot = 3;
	} else {
	FX_NOTREACHED() << "x86: No known hw exception set in DR6";
	return std::nullopt;
	}

	return WatchpointInfo({addr, addr + length}, slot);
	}

	void DebugRegisters::SetForHitWatchpoint(int slot) {
	switch (slot) {
	case 0:
	regs_.dr6 \|= X86_FLAG_MASK(DR6B0);
	break;
	case 1:
	regs_.dr6 \|= X86_FLAG_MASK(DR6B1);
	break;
	case 2:
	regs_.dr6 \|= X86_FLAG_MASK(DR6B2);
	break;
	case 3:
	regs_.dr6 \|= X86_FLAG_MASK(DR6B3);
	break;
	default:
	FX_NOTREACHED() << "Bad slot.";
	break;
	}
	}

	std::string DebugRegisters::ToString() const {
	std::stringstream ss;
	ss << "Regs: " << std::endl
	<< "DR0: 0x" << std::hex << regs_.dr[0] << std::endl
	<< "DR1: 0x" << std::hex << regs_.dr[1] << std::endl
	<< "DR2: 0x" << std::hex << regs_.dr[2] << std::endl
	<< "DR3: 0x" << std::hex << regs_.dr[3] << std::endl
	<< "DR6: " << DR6ToString(regs_.dr6) << std::endl
	<< "DR7: " << DR7ToString(regs_.dr7) << std::endl;
	return ss.str();
	}

	} // namespace debug_agent