GDB Stub: allow to override GDB's handling logic of write watchpoint

Also allow to break on nonmodifying writes.

include/mgba/internal/debugger/gdb-stub.h

@@ -24,6 +24,12 @@ enum GDBStubAckState {
 	GDB_ACK_OFF
 };
 
+enum GDBWatchpointsBehvaior {
+	GDB_WATCHPOINT_STANDARD_LOGIC = 0,
+	GDB_WATCHPOINT_OVERRIDE_LOGIC,
+	GDB_WATCHPOINT_OVERRIDE_LOGIC_ANY_WRITE,
+};
+
 struct GDBStub {
 	struct mDebugger d;
 
@@ -40,10 +46,12 @@ struct GDBStub {
 
 	bool supportsSwbreak;
 	bool supportsHwbreak;
+
+	enum GDBWatchpointsBehvaior watchpointsBehavior;
 };
 
 void GDBStubCreate(struct GDBStub*);
-bool GDBStubListen(struct GDBStub*, int port, const struct Address* bindAddress);
+bool GDBStubListen(struct GDBStub*, int port, const struct Address* bindAddress, enum GDBWatchpointsBehvaior watchpointsBehavior);
 
 void GDBStubHangup(struct GDBStub*);
 void GDBStubShutdown(struct GDBStub*);

src/debugger/debugger.c

@@ -53,7 +53,7 @@ struct mDebugger* mDebuggerCreate(enum mDebuggerType type, struct mCore* core) {
 	case DEBUGGER_GDB:
 #ifdef USE_GDB_STUB
 		GDBStubCreate(&debugger->gdb);
-		GDBStubListen(&debugger->gdb, 2345, 0);
+		GDBStubListen(&debugger->gdb, 2345, 0, GDB_WATCHPOINT_STANDARD_LOGIC);
 		break;
 #endif
 	case DEBUGGER_NONE:

src/debugger/gdb-stub.c

@@ -79,15 +79,18 @@ static void _gdbStubEntered(struct mDebugger* debugger, enum mDebuggerEntryReaso
 	case DEBUGGER_ENTER_WATCHPOINT:
 		if (info) {
 			const char* type = 0;
+
+			if (stub->watchpointsBehavior != GDB_WATCHPOINT_STANDARD_LOGIC && info->type.wp.watchType & WATCHPOINT_WRITE) {
+				// We send S05 instead of T05watch because it bypasses GDB's internal logic to check if
+				// the value changed and to bypass a step into by GDB. This allows to control the change
+				// logic even when using savestates which we already handle in the core debugger logic
+				snprintf(stub->outgoing, GDB_STUB_MAX_LINE - 4, "S%02x", SIGTRAP);
+				_sendMessage(stub);
+				return;
+			}
+
 			switch (info->type.wp.watchType) {
 			case WATCHPOINT_WRITE:
-				if (info->type.wp.newValue == info->type.wp.oldValue) {
-					if (stub->d.state == DEBUGGER_PAUSED) {
-						stub->d.state = DEBUGGER_RUNNING;
-					}
-					return;
-				}
-				// Fall through
 			case WATCHPOINT_WRITE_CHANGE:
 				type = "watch";
 				break;
@@ -575,7 +578,7 @@ static void _setBreakpoint(struct GDBStub* stub, const char* message) {
 		stub->d.platform->setBreakpoint(stub->d.platform, &breakpoint);
 		break;
 	case '2':
-		watchpoint.type = WATCHPOINT_WRITE_CHANGE;
+		watchpoint.type = stub->watchpointsBehavior == GDB_WATCHPOINT_OVERRIDE_LOGIC_ANY_WRITE ? WATCHPOINT_WRITE : WATCHPOINT_WRITE_CHANGE;
 		stub->d.platform->setWatchpoint(stub->d.platform, &watchpoint);
 		break;
 	case '3':
@@ -763,7 +766,7 @@ void GDBStubCreate(struct GDBStub* stub) {
 	stub->shouldBlock = false;
 }
 
-bool GDBStubListen(struct GDBStub* stub, int port, const struct Address* bindAddress) {
+bool GDBStubListen(struct GDBStub* stub, int port, const struct Address* bindAddress, enum GDBWatchpointsBehvaior watchpointsBehavior) {
 	if (!SOCKET_FAILED(stub->socket)) {
 		GDBStubShutdown(stub);
 	}
@@ -780,6 +783,7 @@ bool GDBStubListen(struct GDBStub* stub, int port, const struct Address* bindAdd
 		goto cleanup;
 	}
 
+	stub->watchpointsBehavior = watchpointsBehavior;
 	memset(stub->memoryMapXml, 0, GDB_STUB_MAX_LINE);
 
 	return true;

src/platform/qt/GDBController.cpp

@@ -32,8 +32,12 @@ void GDBController::setBindAddress(const Address& address) {
 	m_bindAddress = address;
 }
 
+void GDBController::setWatchpointsBehavior(int watchpointsBehaviorId) {
+	m_watchpointsBehavior = static_cast<GDBWatchpointsBehvaior>(watchpointsBehaviorId);
+}
+
 void GDBController::listen() {
-	if (GDBStubListen(&m_gdbStub, m_port, &m_bindAddress)) {
+	if (GDBStubListen(&m_gdbStub, m_port, &m_bindAddress, m_watchpointsBehavior)) {
 		if (!isAttached()) {
 			attach();
 		}

src/platform/qt/GDBController.h

@@ -28,6 +28,7 @@ public:
 public slots:
 	void setPort(ushort port);
 	void setBindAddress(const Address&);
+	void setWatchpointsBehavior(int watchpointsBehaviorId);
 	void listen();
 
 signals:
@@ -41,6 +42,7 @@ private:
 
 	ushort m_port = 2345;
 	Address m_bindAddress;
+	enum GDBWatchpointsBehvaior m_watchpointsBehavior = GDB_WATCHPOINT_STANDARD_LOGIC;
 };
 
 }

src/platform/qt/GDBWindow.cpp

@@ -5,6 +5,7 @@
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "GDBWindow.h"
 
+#include <QButtonGroup>
 #include <QGridLayout>
 #include <QGroupBox>
 #include <QLabel>
@@ -12,6 +13,7 @@
 #include <QMessageBox>
 #include <QPushButton>
 #include <QHBoxLayout>
+#include <QRadioButton>
 #include <QVBoxLayout>
 
 #include "GDBController.h"
@@ -47,6 +49,28 @@ GDBWindow::GDBWindow(GDBController* controller, QWidget* parent)
 	connect(m_bindAddressEdit, &QLineEdit::textChanged, this, &GDBWindow::bindAddressChanged);
 	settingsGrid->addWidget(m_bindAddressEdit, 1, 1, Qt::AlignLeft);
 
+	QGroupBox* watchpointsSettings = new QGroupBox(tr("Write watchpoints behavior"));
+	mainSegment->addWidget(watchpointsSettings);
+
+	QVBoxLayout* watchpointsSettingsLayout = new QVBoxLayout;
+	watchpointsSettings->setLayout(watchpointsSettingsLayout);
+
+	QButtonGroup* watchpointsButtonGroup = new QButtonGroup(watchpointsSettings);
+	connect(watchpointsButtonGroup, &QButtonGroup::idClicked, controller, &GDBController::setWatchpointsBehavior);
+
+	m_watchpointsStandardRadio = new QRadioButton(tr("Standard GDB"), watchpointsSettings);
+	m_watchpointsStandardRadio->setChecked(true);
+	watchpointsButtonGroup->addButton(m_watchpointsStandardRadio, GDB_WATCHPOINT_STANDARD_LOGIC);
+	watchpointsSettingsLayout->addWidget(m_watchpointsStandardRadio);
+
+	m_watchpointsOverrideLogicRadio = new QRadioButton(tr("Internal change detection"), watchpointsSettings);
+	watchpointsButtonGroup->addButton(m_watchpointsOverrideLogicRadio, GDB_WATCHPOINT_OVERRIDE_LOGIC);
+	watchpointsSettingsLayout->addWidget(m_watchpointsOverrideLogicRadio);
+
+	m_watchpointsOverrideLogicAnyWriteRadio = new QRadioButton(tr("Break on all writes"), watchpointsSettings);
+	watchpointsButtonGroup->addButton(m_watchpointsOverrideLogicAnyWriteRadio, GDB_WATCHPOINT_OVERRIDE_LOGIC_ANY_WRITE);
+	watchpointsSettingsLayout->addWidget(m_watchpointsOverrideLogicAnyWriteRadio);
+
 	QHBoxLayout* buttons = new QHBoxLayout;
 
 	m_startStopButton = new QPushButton;
@@ -92,6 +116,9 @@ void GDBWindow::bindAddressChanged(const QString& bindAddressString) {
 void GDBWindow::started() {
 	m_portEdit->setEnabled(false);
 	m_bindAddressEdit->setEnabled(false);
+	m_watchpointsStandardRadio->setEnabled(false);
+	m_watchpointsOverrideLogicRadio->setEnabled(false);
+	m_watchpointsOverrideLogicAnyWriteRadio->setEnabled(false);
 	m_startStopButton->setText(tr("Stop"));
 	m_breakButton->setEnabled(true);
 	disconnect(m_startStopButton, &QAbstractButton::clicked, m_gdbController, &GDBController::listen);
@@ -102,6 +129,9 @@ void GDBWindow::started() {
 void GDBWindow::stopped() {
 	m_portEdit->setEnabled(true);
 	m_bindAddressEdit->setEnabled(true);
+	m_watchpointsStandardRadio->setEnabled(true);
+	m_watchpointsOverrideLogicRadio->setEnabled(true);
+	m_watchpointsOverrideLogicAnyWriteRadio->setEnabled(true);
 	m_startStopButton->setText(tr("Start"));
 	m_breakButton->setEnabled(false);
 	disconnect(m_startStopButton, &QAbstractButton::clicked, m_gdbController, &DebuggerController::detach);

src/platform/qt/GDBWindow.h

@@ -9,6 +9,7 @@
 
 class QLineEdit;
 class QPushButton;
+class QRadioButton;
 
 namespace QGBA {
 
@@ -34,6 +35,9 @@ private:
 
 	QLineEdit* m_portEdit;
 	QLineEdit* m_bindAddressEdit;
+	QRadioButton* m_watchpointsStandardRadio;
+	QRadioButton* m_watchpointsOverrideLogicRadio;
+	QRadioButton* m_watchpointsOverrideLogicAnyWriteRadio;
 	QPushButton* m_startStopButton;
 	QPushButton* m_breakButton;
 };