gdb_server: support File-I/O Remote Protocol Extension

The File I/O remote protocol extension allows the target to use the
host's file system and console I/O to perform various system calls.

To use the function, targets need to prepare two callback functions:
* get_gdb_finish_info: to get file I/O parameters from target
* gdb_fileio_end: pass file I/O response to target

As target is halted, gdb_server will try to get file-I/O information
from target through target_get_gdb_fileio_info(). If the callback function
returns ERROR_OK, gdb_server will initiate a file-I/O request to gdb.
After gdb finishes system call, gdb will pass response of the system call
to target through target_gdb_fileio_end() and continue to run(continue or step).

To implement the function, I add a new data structure in struct target,
called struct gdb_fileio_info, to record file I/O name and parameters.

Details refer to GDB manual "File-I/O Remote Protocol Extension"

Change-Id: I7f4d45e7c9e967b6d898dc79ba01d86bc46315d3
Signed-off-by: Hsiangkai Wang <hsiangkai@gmail.com>
Reviewed-on: http://openocd.zylin.com/1102
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>

9 files changed, 776 insertions, 49 deletions

diff --git a/src/server/gdb_server.c b/src/server/gdb_server.c
index 8eacf8c..14925a2 100644
--- a/src/server/gdb_server.c
+++ b/src/server/gdb_server.c
@@ -125,6 +125,9 @@ static int gdb_report_data_abort;
 /* disabled by default */
 static int gdb_use_target_description;
 
+/* current processing free-run type, used by file-I/O */
+static char gdb_running_type;
+
 static int gdb_last_signal(struct target *target)
 {
 	switch (target->debug_reason) {
@@ -691,6 +694,142 @@ static int gdb_output(struct command_context *context, const char *line)
 	return ERROR_OK;
 }
 
+static void gdb_signal_reply(struct target *target, struct connection *connection)
+{
+	struct gdb_connection *gdb_connection = connection->priv;
+	char sig_reply[20];
+	char stop_reason[20];
+	int sig_reply_len;
+	int signal_var;
+
+	if (gdb_connection->ctrl_c) {
+		signal_var = 0x2;
+		gdb_connection->ctrl_c = 0;
+	} else
+		signal_var = gdb_last_signal(target);
+
+	stop_reason[0] = '\0';
+	if (target->debug_reason == DBG_REASON_WATCHPOINT) {
+		enum watchpoint_rw hit_wp_type;
+		uint32_t hit_wp_address;
+
+		if (watchpoint_hit(target, &hit_wp_type, &hit_wp_address) == ERROR_OK) {
+
+			switch (hit_wp_type) {
+				case WPT_WRITE:
+					snprintf(stop_reason, sizeof(stop_reason),
+							"watch:%08x;", hit_wp_address);
+					break;
+				case WPT_READ:
+					snprintf(stop_reason, sizeof(stop_reason),
+							"rwatch:%08x;", hit_wp_address);
+					break;
+				case WPT_ACCESS:
+					snprintf(stop_reason, sizeof(stop_reason),
+							"awatch:%08x;", hit_wp_address);
+					break;
+				default:
+					break;
+			}
+		}
+	}
+
+	sig_reply_len = snprintf(sig_reply, sizeof(sig_reply), "T%2.2x%s",
+			signal_var, stop_reason);
+
+	gdb_put_packet(connection, sig_reply, sig_reply_len);
+	gdb_connection->frontend_state = TARGET_HALTED;
+	rtos_update_threads(target);
+}
+
+static void gdb_fileio_reply(struct target *target, struct connection *connection)
+{
+	struct gdb_connection *gdb_connection = connection->priv;
+	char fileio_command[256];
+	int command_len;
+	bool program_exited = false;
+
+	if (strcmp(target->fileio_info->identifier, "open") == 0)
+		sprintf(fileio_command, "F%s,%x/%x,%x,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2,
+				target->fileio_info->param_3,
+				target->fileio_info->param_4);
+	else if (strcmp(target->fileio_info->identifier, "close") == 0)
+		sprintf(fileio_command, "F%s,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1);
+	else if (strcmp(target->fileio_info->identifier, "read") == 0)
+		sprintf(fileio_command, "F%s,%x,%x,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2,
+				target->fileio_info->param_3);
+	else if (strcmp(target->fileio_info->identifier, "write") == 0)
+		sprintf(fileio_command, "F%s,%x,%x,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2,
+				target->fileio_info->param_3);
+	else if (strcmp(target->fileio_info->identifier, "lseek") == 0)
+		sprintf(fileio_command, "F%s,%x,%x,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2,
+				target->fileio_info->param_3);
+	else if (strcmp(target->fileio_info->identifier, "rename") == 0)
+		sprintf(fileio_command, "F%s,%x/%x,%x/%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2,
+				target->fileio_info->param_3,
+				target->fileio_info->param_4);
+	else if (strcmp(target->fileio_info->identifier, "unlink") == 0)
+		sprintf(fileio_command, "F%s,%x/%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2);
+	else if (strcmp(target->fileio_info->identifier, "stat") == 0)
+		sprintf(fileio_command, "F%s,%x/%x,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2,
+				target->fileio_info->param_3);
+	else if (strcmp(target->fileio_info->identifier, "fstat") == 0)
+		sprintf(fileio_command, "F%s,%x,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2);
+	else if (strcmp(target->fileio_info->identifier, "gettimeofday") == 0)
+		sprintf(fileio_command, "F%s,%x,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2);
+	else if (strcmp(target->fileio_info->identifier, "isatty") == 0)
+		sprintf(fileio_command, "F%s,%x", target->fileio_info->identifier,
+				target->fileio_info->param_1);
+	else if (strcmp(target->fileio_info->identifier, "system") == 0)
+		sprintf(fileio_command, "F%s,%x/%x", target->fileio_info->identifier,
+				target->fileio_info->param_1,
+				target->fileio_info->param_2);
+	else if (strcmp(target->fileio_info->identifier, "exit") == 0) {
+		/* If target hits exit syscall, report to GDB the program is terminated.
+		 * In addition, let target run its own exit syscall handler. */
+		program_exited = true;
+		sprintf(fileio_command, "W%02x", target->fileio_info->param_1);
+	} else {
+		LOG_DEBUG("Unknown syscall: %s", target->fileio_info->identifier);
+
+		/* encounter unknown syscall, continue */
+		gdb_connection->frontend_state = TARGET_RUNNING;
+		target_resume(target, 1, 0x0, 0, 0);
+		return;
+	}
+
+	command_len = strlen(fileio_command);
+	gdb_put_packet(connection, fileio_command, command_len);
+
+	if (program_exited) {
+		/* Use target_resume() to let target run its own exit syscall handler. */
+		gdb_connection->frontend_state = TARGET_RUNNING;
+		target_resume(target, 1, 0x0, 0, 0);
+	} else {
+		gdb_connection->frontend_state = TARGET_HALTED;
+		rtos_update_threads(target);
+	}
+}
+
 static void gdb_frontend_halted(struct target *target, struct connection *connection)
 {
 	struct gdb_connection *gdb_connection = connection->priv;
@@ -705,52 +844,14 @@ static void gdb_frontend_halted(struct target *target, struct connection *connec
 	 * that are to be ignored.
 	 */
 	if (gdb_connection->frontend_state == TARGET_RUNNING) {
-		char sig_reply[20];
-		char stop_reason[20];
-		int sig_reply_len;
-		int signal_var;
-
 		/* stop forwarding log packets! */
 		log_remove_callback(gdb_log_callback, connection);
 
-		if (gdb_connection->ctrl_c) {
-			signal_var = 0x2;
-			gdb_connection->ctrl_c = 0;
-		} else
-			signal_var = gdb_last_signal(target);
-
-		stop_reason[0] = '\0';
-		if (target->debug_reason == DBG_REASON_WATCHPOINT) {
-			enum watchpoint_rw hit_wp_type;
-			uint32_t hit_wp_address;
-
-			if (watchpoint_hit(target, &hit_wp_type, &hit_wp_address) == ERROR_OK) {
-
-				switch (hit_wp_type) {
-					case WPT_WRITE:
-						snprintf(stop_reason, sizeof(stop_reason),
-								"watch:%08x;", hit_wp_address);
-						break;
-					case WPT_READ:
-						snprintf(stop_reason, sizeof(stop_reason),
-								"rwatch:%08x;", hit_wp_address);
-						break;
-					case WPT_ACCESS:
-						snprintf(stop_reason, sizeof(stop_reason),
-								"awatch:%08x;", hit_wp_address);
-						break;
-					default:
-						break;
-				}
-			}
-		}
-
-		sig_reply_len = snprintf(sig_reply, sizeof(sig_reply), "T%2.2x%s",
-				signal_var, stop_reason);
-
-		gdb_put_packet(connection, sig_reply, sig_reply_len);
-		gdb_connection->frontend_state = TARGET_HALTED;
-		rtos_update_threads(target);
+		/* check fileio first */
+		if (target_get_gdb_fileio_info(target, target->fileio_info) == ERROR_OK)
+			gdb_fileio_reply(target, connection);
+		else
+			gdb_signal_reply(target, connection);
 	}
 }
 
@@ -1391,6 +1492,7 @@ static int gdb_step_continue_packet(struct connection *connection,
 	} else
 		current = 1;
 
+	gdb_running_type = packet[0];
 	if (packet[0] == 'c') {
 		LOG_DEBUG("continue");
 		/* resume at current address, don't handle breakpoints, not debugging */
@@ -2315,6 +2417,54 @@ static int gdb_detach(struct connection *connection)
 	return gdb_put_packet(connection, "OK", 2);
 }
 
+/* The format of 'F' response packet is
+ * Fretcode,errno,Ctrl-C flag;call-specific attachment
+ */
+static int gdb_fileio_response_packet(struct connection *connection,
+		char *packet, int packet_size)
+{
+	struct target *target = get_target_from_connection(connection);
+	char *separator;
+	char *parsing_point;
+	int fileio_retcode = strtoul(packet + 1, &separator, 16);
+	int fileio_errno = 0;
+	bool fileio_ctrl_c = false;
+	int retval;
+
+	LOG_DEBUG("-");
+
+	if (*separator == ',') {
+		parsing_point = separator + 1;
+		fileio_errno = strtoul(parsing_point, &separator, 16);
+		if (*separator == ',') {
+			if (*(separator + 1) == 'C') {
+				/* TODO: process ctrl-c */
+				fileio_ctrl_c = true;
+			}
+		}
+	}
+
+	LOG_DEBUG("File-I/O response, retcode: 0x%x, errno: 0x%x, ctrl-c: %s",
+			fileio_retcode, fileio_errno, fileio_ctrl_c ? "true" : "false");
+
+	retval = target_gdb_fileio_end(target, fileio_retcode, fileio_errno, fileio_ctrl_c);
+	if (retval != ERROR_OK)
+		return ERROR_FAIL;
+
+	/* After File-I/O ends, keep continue or step */
+	if (gdb_running_type == 'c')
+		retval = target_resume(target, 1, 0x0, 0, 0);
+	else if (gdb_running_type == 's')
+		retval = target_step(target, 1, 0x0, 0);
+	else
+		retval = ERROR_FAIL;
+
+	if (retval != ERROR_OK)
+		return ERROR_FAIL;
+
+	return ERROR_OK;
+}
+
 static void gdb_log_callback(void *priv, const char *file, unsigned line,
 		const char *function, const char *string)
 {
@@ -2541,6 +2691,19 @@ static int gdb_input_inner(struct connection *connection)
 					gdb_write_smp_packet(connection, packet, packet_size);
 					break;
 
+				case 'F':
+					/* File-I/O extension */
+					/* After gdb uses host-side syscall to complete target file
+					 * I/O, gdb sends host-side syscall return value to target
+					 * by 'F' packet.
+					 * The format of 'F' response packet is
+					 * Fretcode,errno,Ctrl-C flag;call-specific attachment
+					 */
+					gdb_con->frontend_state = TARGET_RUNNING;
+					log_add_callback(gdb_log_callback, connection);
+					gdb_fileio_response_packet(connection, packet, packet_size);
+					break;
+
 				default:
 					/* ignore unknown packets */
 					LOG_DEBUG("ignoring 0x%2.2x packet", packet[0]);
diff --git a/src/target/nds32.c b/src/target/nds32.c
index 95a249d..c4bd63a 100644
--- a/src/target/nds32.c
+++ b/src/target/nds32.c
@@ -1645,6 +1645,10 @@ int nds32_init_arch_info(struct target *target, struct nds32 *nds32)
 	nds32->keep_target_edm_ctl = false;
 	nds32->word_access_mem = false;
 	nds32->virtual_hosting = false;
+	nds32->hit_syscall = false;
+	nds32->active_syscall_id = NDS32_SYSCALL_UNDEFINED;
+	nds32->virtual_hosting_errno = 0;
+	nds32->virtual_hosting_ctrl_c = false;
 
 	nds32_reg_init();
 
@@ -1772,13 +1776,24 @@ int nds32_step(struct target *target, int current,
 		ir14_value &= ~(0x1 << 31);
 	nds32_set_mapped_reg(nds32, IR14, ir14_value);
 
+	/* check hit_syscall before leave_debug_state() because
+	 * leave_debug_state() may clear hit_syscall flag */
+	bool no_step = false;
+	if (nds32->hit_syscall)
+		/* step after hit_syscall should be ignored because
+		 * leave_debug_state will step implicitly to skip the
+		 * syscall */
+		no_step = true;
+
 	/********* TODO: maybe create another function to handle this part */
 	CHECK_RETVAL(nds32->leave_debug_state(nds32, true));
 	CHECK_RETVAL(target_call_event_callbacks(target, TARGET_EVENT_RESUMED));
 
-	struct aice_port_s *aice = target_to_aice(target);
-	if (ERROR_OK != aice_step(aice))
-		return ERROR_FAIL;
+	if (no_step == false) {
+		struct aice_port_s *aice = target_to_aice(target);
+		if (ERROR_OK != aice_step(aice))
+			return ERROR_FAIL;
+	}
 
 	/* save state */
 	CHECK_RETVAL(nds32->enter_debug_state(nds32, true));
@@ -1878,6 +1893,12 @@ int nds32_examine_debug_reason(struct nds32 *nds32)
 	uint32_t reason;
 	struct target *target = nds32->target;
 
+	if (nds32->hit_syscall == true) {
+		LOG_DEBUG("Hit syscall breakpoint");
+		target->debug_reason = DBG_REASON_BREAKPOINT;
+		return ERROR_OK;
+	}
+
 	nds32->get_debug_reason(nds32, &reason);
 
 	LOG_DEBUG("nds32 examines debug reason: %s", nds32_debug_type_name[reason]);
@@ -2110,8 +2131,11 @@ int nds32_resume(struct target *target, int current,
 	CHECK_RETVAL(nds32->leave_debug_state(nds32, true));
 	CHECK_RETVAL(target_call_event_callbacks(target, TARGET_EVENT_RESUMED));
 
-	struct aice_port_s *aice = target_to_aice(target);
-	aice_run(aice);
+	if (nds32->virtual_hosting_ctrl_c == false) {
+		struct aice_port_s *aice = target_to_aice(target);
+		aice_run(aice);
+	} else
+		nds32->virtual_hosting_ctrl_c = false;
 
 	target->debug_reason = DBG_REASON_NOTHALTED;
 	if (!debug_execution)
@@ -2239,6 +2263,292 @@ int nds32_init(struct nds32 *nds32)
 	return ERROR_OK;
 }
 
+int nds32_get_gdb_fileio_info(struct target *target, struct gdb_fileio_info *fileio_info)
+{
+	/* fill syscall parameters to file-I/O info */
+	if (NULL == fileio_info) {
+		LOG_ERROR("Target has not initial file-I/O data structure");
+		return ERROR_FAIL;
+	}
+
+	struct nds32 *nds32 = target_to_nds32(target);
+	uint32_t value_ir6;
+	uint32_t syscall_id;
+
+	if (nds32->hit_syscall == false)
+		return ERROR_FAIL;
+
+	nds32_get_mapped_reg(nds32, IR6, &value_ir6);
+	syscall_id = (value_ir6 >> 16) & 0x7FFF;
+	nds32->active_syscall_id = syscall_id;
+
+	LOG_DEBUG("hit syscall ID: 0x%x", syscall_id);
+
+	/* free previous identifier storage */
+	if (NULL != fileio_info->identifier) {
+		free(fileio_info->identifier);
+		fileio_info->identifier = NULL;
+	}
+
+	switch (syscall_id) {
+		case NDS32_SYSCALL_EXIT:
+			fileio_info->identifier = (char *)malloc(5);
+			sprintf(fileio_info->identifier, "exit");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			break;
+		case NDS32_SYSCALL_OPEN:
+			{
+				uint8_t filename[256];
+				fileio_info->identifier = (char *)malloc(5);
+				sprintf(fileio_info->identifier, "open");
+				nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+				/* reserve fileio_info->param_2 for length of path */
+				nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_3));
+				nds32_get_mapped_reg(nds32, R2, &(fileio_info->param_4));
+
+				target->type->read_buffer(target, fileio_info->param_1,
+						256, filename);
+				fileio_info->param_2 = strlen((char *)filename) + 1;
+			}
+			break;
+		case NDS32_SYSCALL_CLOSE:
+			fileio_info->identifier = (char *)malloc(6);
+			sprintf(fileio_info->identifier, "close");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			break;
+		case NDS32_SYSCALL_READ:
+			fileio_info->identifier = (char *)malloc(5);
+			sprintf(fileio_info->identifier, "read");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_2));
+			nds32_get_mapped_reg(nds32, R2, &(fileio_info->param_3));
+			break;
+		case NDS32_SYSCALL_WRITE:
+			fileio_info->identifier = (char *)malloc(6);
+			sprintf(fileio_info->identifier, "write");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_2));
+			nds32_get_mapped_reg(nds32, R2, &(fileio_info->param_3));
+			break;
+		case NDS32_SYSCALL_LSEEK:
+			fileio_info->identifier = (char *)malloc(6);
+			sprintf(fileio_info->identifier, "lseek");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_2));
+			nds32_get_mapped_reg(nds32, R2, &(fileio_info->param_3));
+			break;
+		case NDS32_SYSCALL_UNLINK:
+			{
+				uint8_t filename[256];
+				fileio_info->identifier = (char *)malloc(7);
+				sprintf(fileio_info->identifier, "unlink");
+				nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+				/* reserve fileio_info->param_2 for length of path */
+
+				target->type->read_buffer(target, fileio_info->param_1,
+						256, filename);
+				fileio_info->param_2 = strlen((char *)filename) + 1;
+			}
+			break;
+		case NDS32_SYSCALL_RENAME:
+			{
+				uint8_t filename[256];
+				fileio_info->identifier = (char *)malloc(7);
+				sprintf(fileio_info->identifier, "rename");
+				nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+				/* reserve fileio_info->param_2 for length of old path */
+				nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_3));
+				/* reserve fileio_info->param_4 for length of new path */
+
+				target->type->read_buffer(target, fileio_info->param_1,
+						256, filename);
+				fileio_info->param_2 = strlen((char *)filename) + 1;
+
+				target->type->read_buffer(target, fileio_info->param_3,
+						256, filename);
+				fileio_info->param_4 = strlen((char *)filename) + 1;
+			}
+			break;
+		case NDS32_SYSCALL_FSTAT:
+			fileio_info->identifier = (char *)malloc(6);
+			sprintf(fileio_info->identifier, "fstat");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_2));
+			break;
+		case NDS32_SYSCALL_STAT:
+			{
+				uint8_t filename[256];
+				fileio_info->identifier = (char *)malloc(5);
+				sprintf(fileio_info->identifier, "stat");
+				nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+				/* reserve fileio_info->param_2 for length of old path */
+				nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_3));
+
+				target->type->read_buffer(target, fileio_info->param_1,
+						256, filename);
+				fileio_info->param_2 = strlen((char *)filename) + 1;
+			}
+			break;
+		case NDS32_SYSCALL_GETTIMEOFDAY:
+			fileio_info->identifier = (char *)malloc(13);
+			sprintf(fileio_info->identifier, "gettimeofday");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			nds32_get_mapped_reg(nds32, R1, &(fileio_info->param_2));
+			break;
+		case NDS32_SYSCALL_ISATTY:
+			fileio_info->identifier = (char *)malloc(7);
+			sprintf(fileio_info->identifier, "isatty");
+			nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+			break;
+		case NDS32_SYSCALL_SYSTEM:
+			{
+				uint8_t command[256];
+				fileio_info->identifier = (char *)malloc(7);
+				sprintf(fileio_info->identifier, "system");
+				nds32_get_mapped_reg(nds32, R0, &(fileio_info->param_1));
+				/* reserve fileio_info->param_2 for length of old path */
+
+				target->type->read_buffer(target, fileio_info->param_1,
+						256, command);
+				fileio_info->param_2 = strlen((char *)command) + 1;
+			}
+			break;
+		case NDS32_SYSCALL_ERRNO:
+			fileio_info->identifier = (char *)malloc(6);
+			sprintf(fileio_info->identifier, "errno");
+			nds32_set_mapped_reg(nds32, R0, nds32->virtual_hosting_errno);
+			break;
+		default:
+			fileio_info->identifier = (char *)malloc(8);
+			sprintf(fileio_info->identifier, "unknown");
+			break;
+	}
+
+	return ERROR_OK;
+}
+
+int nds32_gdb_fileio_end(struct target *target, int retcode, int fileio_errno, bool ctrl_c)
+{
+	LOG_DEBUG("syscall return code: 0x%x, errno: 0x%x, ctrl_c: %s",
+			retcode, fileio_errno, ctrl_c ? "true" : "false");
+
+	struct nds32 *nds32 = target_to_nds32(target);
+
+	nds32_set_mapped_reg(nds32, R0, (uint32_t)retcode);
+
+	nds32->virtual_hosting_errno = fileio_errno;
+	nds32->virtual_hosting_ctrl_c = ctrl_c;
+	nds32->active_syscall_id = NDS32_SYSCALL_UNDEFINED;
+
+	return ERROR_OK;
+}
+
+int nds32_gdb_fileio_write_memory(struct nds32 *nds32, uint32_t address,
+		uint32_t size, const uint8_t *buffer)
+{
+	if ((NDS32_SYSCALL_FSTAT == nds32->active_syscall_id) ||
+			(NDS32_SYSCALL_STAT == nds32->active_syscall_id)) {
+		/* If doing GDB file-I/O, target should convert 'struct stat'
+		 * from gdb-format to target-format */
+		uint8_t stat_buffer[NDS32_STRUCT_STAT_SIZE];
+		/* st_dev 2 */
+		stat_buffer[0] = buffer[3];
+		stat_buffer[1] = buffer[2];
+		/* st_ino 2 */
+		stat_buffer[2] = buffer[7];
+		stat_buffer[3] = buffer[6];
+		/* st_mode 4 */
+		stat_buffer[4] = buffer[11];
+		stat_buffer[5] = buffer[10];
+		stat_buffer[6] = buffer[9];
+		stat_buffer[7] = buffer[8];
+		/* st_nlink 2 */
+		stat_buffer[8] = buffer[15];
+		stat_buffer[9] = buffer[16];
+		/* st_uid 2 */
+		stat_buffer[10] = buffer[19];
+		stat_buffer[11] = buffer[18];
+		/* st_gid 2 */
+		stat_buffer[12] = buffer[23];
+		stat_buffer[13] = buffer[22];
+		/* st_rdev 2 */
+		stat_buffer[14] = buffer[27];
+		stat_buffer[15] = buffer[26];
+		/* st_size 4 */
+		stat_buffer[16] = buffer[35];
+		stat_buffer[17] = buffer[34];
+		stat_buffer[18] = buffer[33];
+		stat_buffer[19] = buffer[32];
+		/* st_atime 4 */
+		stat_buffer[20] = buffer[55];
+		stat_buffer[21] = buffer[54];
+		stat_buffer[22] = buffer[53];
+		stat_buffer[23] = buffer[52];
+		/* st_spare1 4 */
+		stat_buffer[24] = 0;
+		stat_buffer[25] = 0;
+		stat_buffer[26] = 0;
+		stat_buffer[27] = 0;
+		/* st_mtime 4 */
+		stat_buffer[28] = buffer[59];
+		stat_buffer[29] = buffer[58];
+		stat_buffer[30] = buffer[57];
+		stat_buffer[31] = buffer[56];
+		/* st_spare2 4 */
+		stat_buffer[32] = 0;
+		stat_buffer[33] = 0;
+		stat_buffer[34] = 0;
+		stat_buffer[35] = 0;
+		/* st_ctime 4 */
+		stat_buffer[36] = buffer[63];
+		stat_buffer[37] = buffer[62];
+		stat_buffer[38] = buffer[61];
+		stat_buffer[39] = buffer[60];
+		/* st_spare3 4 */
+		stat_buffer[40] = 0;
+		stat_buffer[41] = 0;
+		stat_buffer[42] = 0;
+		stat_buffer[43] = 0;
+		/* st_blksize 4 */
+		stat_buffer[44] = buffer[43];
+		stat_buffer[45] = buffer[42];
+		stat_buffer[46] = buffer[41];
+		stat_buffer[47] = buffer[40];
+		/* st_blocks 4 */
+		stat_buffer[48] = buffer[51];
+		stat_buffer[49] = buffer[50];
+		stat_buffer[50] = buffer[49];
+		stat_buffer[51] = buffer[48];
+		/* st_spare4 8 */
+		stat_buffer[52] = 0;
+		stat_buffer[53] = 0;
+		stat_buffer[54] = 0;
+		stat_buffer[55] = 0;
+		stat_buffer[56] = 0;
+		stat_buffer[57] = 0;
+		stat_buffer[58] = 0;
+		stat_buffer[59] = 0;
+
+		return nds32_write_buffer(nds32->target, address, NDS32_STRUCT_STAT_SIZE, stat_buffer);
+	} else if (NDS32_SYSCALL_GETTIMEOFDAY == nds32->active_syscall_id) {
+		/* If doing GDB file-I/O, target should convert 'struct timeval'
+		 * from gdb-format to target-format */
+		uint8_t timeval_buffer[NDS32_STRUCT_TIMEVAL_SIZE];
+		timeval_buffer[0] = buffer[3];
+		timeval_buffer[1] = buffer[2];
+		timeval_buffer[2] = buffer[1];
+		timeval_buffer[3] = buffer[0];
+		timeval_buffer[4] = buffer[11];
+		timeval_buffer[5] = buffer[10];
+		timeval_buffer[6] = buffer[9];
+		timeval_buffer[7] = buffer[8];
+
+		return nds32_write_buffer(nds32->target, address, NDS32_STRUCT_TIMEVAL_SIZE, timeval_buffer);
+	}
+
+	return nds32_write_buffer(nds32->target, address, size, buffer);
+}
+
 int nds32_reset_halt(struct nds32 *nds32)
 {
 	LOG_INFO("reset halt as init");
diff --git a/src/target/nds32.h b/src/target/nds32.h
index b7e787c..8acd915 100644
--- a/src/target/nds32.h
+++ b/src/target/nds32.h
@@ -284,6 +284,18 @@ struct nds32 {
 	/** Flag reporting whether virtual hosting is active. */
 	bool virtual_hosting;
 
+	/** Flag reporting whether continue/step hits syscall or not */
+	bool hit_syscall;
+
+	/** Value to be returned by virtual hosting SYS_ERRNO request. */
+	int virtual_hosting_errno;
+
+	/** Flag reporting whether syscall is aborted */
+	bool virtual_hosting_ctrl_c;
+
+	/** Record syscall ID for other operations to do special processing for target */
+	int active_syscall_id;
+
 	/** Flag reporting whether global stop is active. */
 	bool global_stop;
 
@@ -404,6 +416,10 @@ extern int nds32_resume(struct target *target, int current,
 		uint32_t address, int handle_breakpoints, int debug_execution);
 extern int nds32_assert_reset(struct target *target);
 extern int nds32_init(struct nds32 *nds32);
+extern int nds32_get_gdb_fileio_info(struct target *target, struct gdb_fileio_info *fileio_info);
+extern int nds32_gdb_fileio_write_memory(struct nds32 *nds32, uint32_t address,
+		uint32_t size, const uint8_t *buffer);
+extern int nds32_gdb_fileio_end(struct target *target, int retcode, int fileio_errno, bool ctrl_c);
 extern int nds32_reset_halt(struct nds32 *nds32);
 extern int nds32_login(struct nds32 *nds32);
 
diff --git a/src/target/nds32_v3.c b/src/target/nds32_v3.c
index 868260d..766e5cc 100644
--- a/src/target/nds32_v3.c
+++ b/src/target/nds32_v3.c
@@ -520,4 +520,7 @@ struct target_type nds32_v3_target = {
 	.target_create = nds32_v3_target_create,
 	.init_target = nds32_v3_init_target,
 	.examine = nds32_v3_examine,
+
+	.get_gdb_fileio_info = nds32_get_gdb_fileio_info,
+	.gdb_fileio_end = nds32_gdb_fileio_end,
 };
diff --git a/src/target/nds32_v3_common.c b/src/target/nds32_v3_common.c
index 2fbd1a3..f0cd77d 100644
--- a/src/target/nds32_v3_common.c
+++ b/src/target/nds32_v3_common.c
@@ -29,6 +29,18 @@
 #include "nds32_aice.h"
 #include "nds32_v3_common.h"
 
+static struct breakpoint syscall_breakpoint = {
+	0x80,
+	0,
+	4,
+	BKPT_SOFT,
+	0,
+	NULL,
+	NULL,
+	0x515CA11,
+	0,
+};
+
 static struct nds32_v3_common_callback *v3_common_callback;
 
 static int nds32_v3_register_mapping(struct nds32 *nds32, int reg_no)
@@ -80,6 +92,22 @@ static int nds32_v3_debug_entry(struct nds32 *nds32, bool enable_watchpoint)
 	if (enable_watchpoint)
 		CHECK_RETVAL(v3_common_callback->deactivate_hardware_watchpoint(nds32->target));
 
+	if (nds32->virtual_hosting) {
+		if (syscall_breakpoint.set) {
+			/** disable virtual hosting */
+
+			/* remove breakpoint at syscall entry */
+			target_remove_breakpoint(nds32->target, &syscall_breakpoint);
+			syscall_breakpoint.set = 0;
+
+			uint32_t value_pc;
+			nds32_get_mapped_reg(nds32, PC, &value_pc);
+			if (value_pc == syscall_breakpoint.address)
+				/** process syscall for virtual hosting */
+				nds32->hit_syscall = true;
+		}
+	}
+
 	if (ERROR_OK != nds32_examine_debug_reason(nds32)) {
 		nds32->target->state = backup_state;
 
@@ -132,6 +160,74 @@ static int nds32_v3_leave_debug_state(struct nds32 *nds32, bool enable_watchpoin
 	 */
 	CHECK_RETVAL(nds32_restore_context(target));
 
+	if (nds32->virtual_hosting) {
+		/** enable virtual hosting */
+		uint32_t value_ir3;
+		uint32_t entry_size;
+		uint32_t syscall_address;
+
+		/* get syscall entry address */
+		nds32_get_mapped_reg(nds32, IR3, &value_ir3);
+		entry_size = 0x4 << (((value_ir3 >> 14) & 0x3) << 1);
+		syscall_address = (value_ir3 & 0xFFFF0000) + entry_size * 8; /* The index of SYSCALL is 8 */
+
+		if (nds32->hit_syscall) {
+			/* single step to skip syscall entry */
+			/* use IRET to skip syscall */
+			struct aice_port_s *aice = target_to_aice(target);
+			uint32_t value_ir9;
+			uint32_t value_ir6;
+			uint32_t syscall_id;
+
+			nds32_get_mapped_reg(nds32, IR6, &value_ir6);
+			syscall_id = (value_ir6 >> 16) & 0x7FFF;
+
+			if (syscall_id == NDS32_SYSCALL_EXIT) {
+				/* If target hits exit syscall, do not use IRET to skip handler. */
+				aice_step(aice);
+			} else {
+				/* use api->read/write_reg to skip nds32 register cache */
+				uint32_t value_dimbr;
+				aice_read_debug_reg(aice, NDS_EDM_SR_DIMBR, &value_dimbr);
+				aice_write_register(aice, IR11, value_dimbr + 0xC);
+
+				aice_read_register(aice, IR9, &value_ir9);
+				value_ir9 += 4; /* syscall is always 4 bytes */
+				aice_write_register(aice, IR9, value_ir9);
+
+				/* backup hardware breakpoint 0 */
+				uint32_t backup_bpa, backup_bpam, backup_bpc;
+				aice_read_debug_reg(aice, NDS_EDM_SR_BPA0, &backup_bpa);
+				aice_read_debug_reg(aice, NDS_EDM_SR_BPAM0, &backup_bpam);
+				aice_read_debug_reg(aice, NDS_EDM_SR_BPC0, &backup_bpc);
+
+				/* use hardware breakpoint 0 to stop cpu after skipping syscall */
+				aice_write_debug_reg(aice, NDS_EDM_SR_BPA0, value_ir9);
+				aice_write_debug_reg(aice, NDS_EDM_SR_BPAM0, 0);
+				aice_write_debug_reg(aice, NDS_EDM_SR_BPC0, 0xA);
+
+				/* Execute two IRET.
+				 * First IRET is used to quit debug mode.
+				 * Second IRET is used to quit current syscall. */
+				uint32_t dim_inst[4] = {NOP, NOP, IRET, IRET};
+				aice_execute(aice, dim_inst, 4);
+
+				/* restore origin hardware breakpoint 0 */
+				aice_write_debug_reg(aice, NDS_EDM_SR_BPA0, backup_bpa);
+				aice_write_debug_reg(aice, NDS_EDM_SR_BPAM0, backup_bpam);
+				aice_write_debug_reg(aice, NDS_EDM_SR_BPC0, backup_bpc);
+			}
+
+			nds32->hit_syscall = false;
+		}
+
+		/* insert breakpoint at syscall entry */
+		syscall_breakpoint.address = syscall_address;
+		syscall_breakpoint.type = BKPT_SOFT;
+		syscall_breakpoint.set = 1;
+		target_add_breakpoint(target, &syscall_breakpoint);
+	}
+
 	/* enable polling */
 	jtag_poll_set_enabled(true);
 
@@ -398,7 +494,27 @@ int nds32_v3_read_buffer(struct target *target, uint32_t address,
 	else
 		return ERROR_FAIL;
 
-	return nds32_read_buffer(target, address, size, buffer);
+	int result;
+	struct aice_port_s *aice = target_to_aice(target);
+	/* give arbitrary initial value to avoid warning messages */
+	enum nds_memory_access origin_access_channel = NDS_MEMORY_ACC_CPU;
+
+	if (nds32->hit_syscall) {
+		/* Use bus mode to access memory during virtual hosting */
+		origin_access_channel = memory->access_channel;
+		memory->access_channel = NDS_MEMORY_ACC_BUS;
+		aice_memory_access(aice, NDS_MEMORY_ACC_BUS);
+	}
+
+	result = nds32_read_buffer(target, address, size, buffer);
+
+	if (nds32->hit_syscall) {
+		/* Restore access_channel after virtual hosting */
+		memory->access_channel = origin_access_channel;
+		aice_memory_access(aice, origin_access_channel);
+	}
+
+	return result;
 }
 
 int nds32_v3_write_buffer(struct target *target, uint32_t address,
@@ -436,6 +552,24 @@ int nds32_v3_write_buffer(struct target *target, uint32_t address,
 	else
 		return ERROR_FAIL;
 
+	if (nds32->hit_syscall) {
+		/* Use bus mode to access memory during virtual hosting */
+		struct aice_port_s *aice = target_to_aice(target);
+		enum nds_memory_access origin_access_channel;
+		int result;
+
+		origin_access_channel = memory->access_channel;
+		memory->access_channel = NDS_MEMORY_ACC_BUS;
+		aice_memory_access(aice, NDS_MEMORY_ACC_BUS);
+
+		result = nds32_gdb_fileio_write_memory(nds32, address, size, buffer);
+
+		memory->access_channel = origin_access_channel;
+		aice_memory_access(aice, origin_access_channel);
+
+		return result;
+	}
+
 	return nds32_write_buffer(target, address, size, buffer);
 }
 
@@ -474,10 +608,26 @@ int nds32_v3_read_memory(struct target *target, uint32_t address,
 	else
 		return ERROR_FAIL;
 
+	struct aice_port_s *aice = target_to_aice(target);
+	/* give arbitrary initial value to avoid warning messages */
+	enum nds_memory_access origin_access_channel = NDS_MEMORY_ACC_CPU;
 	int result;
 
+	if (nds32->hit_syscall) {
+		/* Use bus mode to access memory during virtual hosting */
+		origin_access_channel = memory->access_channel;
+		memory->access_channel = NDS_MEMORY_ACC_BUS;
+		aice_memory_access(aice, NDS_MEMORY_ACC_BUS);
+	}
+
 	result = nds32_read_memory(target, address, size, count, buffer);
 
+	if (nds32->hit_syscall) {
+		/* Restore access_channel after virtual hosting */
+		memory->access_channel = origin_access_channel;
+		aice_memory_access(aice, origin_access_channel);
+	}
+
 	return result;
 }
 
@@ -527,5 +677,8 @@ int nds32_v3_init_target(struct command_context *cmd_ctx,
 
 	nds32_init(nds32);
 
+	target->fileio_info = malloc(sizeof(struct gdb_fileio_info));
+	target->fileio_info->identifier = NULL;
+
 	return ERROR_OK;
 }
diff --git a/src/target/nds32_v3m.c b/src/target/nds32_v3m.c
index c37798a..d72d986 100644
--- a/src/target/nds32_v3m.c
+++ b/src/target/nds32_v3m.c
@@ -508,4 +508,7 @@ struct target_type nds32_v3m_target = {
 	.target_create = nds32_v3m_target_create,
 	.init_target = nds32_v3_init_target,
 	.examine = nds32_v3m_examine,
+
+	.get_gdb_fileio_info = nds32_get_gdb_fileio_info,
+	.gdb_fileio_end = nds32_gdb_fileio_end,
 };
diff --git a/src/target/target.c b/src/target/target.c
index 4c31fbe..442f0d9 100644
--- a/src/target/target.c
+++ b/src/target/target.c
@@ -68,6 +68,10 @@ static int target_array2mem(Jim_Interp *interp, struct target *target,
 static int target_mem2array(Jim_Interp *interp, struct target *target,
 		int argc, Jim_Obj * const *argv);
 static int target_register_user_commands(struct command_context *cmd_ctx);
+static int target_get_gdb_fileio_info_default(struct target *target,
+		struct gdb_fileio_info *fileio_info);
+static int target_gdb_fileio_end_default(struct target *target, int retcode,
+		int fileio_errno, bool ctrl_c);
 
 /* targets */
 extern struct target_type arm7tdmi_target;
@@ -1065,6 +1069,24 @@ int target_step(struct target *target,
 	return target->type->step(target, current, address, handle_breakpoints);
 }
 
+int target_get_gdb_fileio_info(struct target *target, struct gdb_fileio_info *fileio_info)
+{
+	if (target->state != TARGET_HALTED) {
+		LOG_WARNING("target %s is not halted", target->cmd_name);
+		return ERROR_TARGET_NOT_HALTED;
+	}
+	return target->type->get_gdb_fileio_info(target, fileio_info);
+}
+
+int target_gdb_fileio_end(struct target *target, int retcode, int fileio_errno, bool ctrl_c)
+{
+	if (target->state != TARGET_HALTED) {
+		LOG_WARNING("target %s is not halted", target->cmd_name);
+		return ERROR_TARGET_NOT_HALTED;
+	}
+	return target->type->gdb_fileio_end(target, retcode, fileio_errno, ctrl_c);
+}
+
 /**
  * Reset the @c examined flag for the given target.
  * Pure paranoia -- targets are zeroed on allocation.
@@ -1151,6 +1173,12 @@ static int target_init_one(struct command_context *cmd_ctx,
 	if (target->type->bulk_write_memory == NULL)
 		target->type->bulk_write_memory = target_bulk_write_memory_default;
 
+	if (target->type->get_gdb_fileio_info == NULL)
+		target->type->get_gdb_fileio_info = target_get_gdb_fileio_info_default;
+
+	if (target->type->gdb_fileio_end == NULL)
+		target->type->gdb_fileio_end = target_gdb_fileio_end_default;
+
 	return ERROR_OK;
 }
 
@@ -1700,6 +1728,20 @@ int target_arch_state(struct target *target)
 	return retval;
 }
 
+static int target_get_gdb_fileio_info_default(struct target *target,
+		struct gdb_fileio_info *fileio_info)
+{
+	LOG_ERROR("Not implemented: %s", __func__);
+	return ERROR_FAIL;
+}
+
+static int target_gdb_fileio_end_default(struct target *target,
+		int retcode, int fileio_errno, bool ctrl_c)
+{
+	LOG_ERROR("Not implemented: %s", __func__);
+	return ERROR_OK;
+}
+
 /* Single aligned words are guaranteed to use 16 or 32 bit access
  * mode respectively, otherwise data is handled as quickly as
  * possible
diff --git a/src/target/target.h b/src/target/target.h
index 09895bb..ee282b1 100644
--- a/src/target/target.h
+++ b/src/target/target.h
@@ -41,6 +41,7 @@ struct watchpoint;
 struct mem_param;
 struct reg_param;
 struct target_list;
+struct gdb_fileio_info;
 
 /*
  * TARGET_UNKNOWN = 0: we don't know anything about the target yet
@@ -191,6 +192,9 @@ struct target {
 	 * the target attached to the gdb is changing dynamically by changing
 	 * gdb_service->target pointer */
 	struct gdb_service *gdb_service;
+
+	/* file-I/O information for host to do syscall */
+	struct gdb_fileio_info *fileio_info;
 };
 
 struct target_list {
@@ -198,6 +202,14 @@ struct target_list {
 	struct target_list *next;
 };
 
+struct gdb_fileio_info {
+	char *identifier;
+	uint32_t param_1;
+	uint32_t param_2;
+	uint32_t param_3;
+	uint32_t param_4;
+};
+
 /** Returns the instance-specific name of the specified target. */
 static inline const char *target_name(struct target *target)
 {
@@ -534,6 +546,22 @@ int target_blank_check_memory(struct target *target,
 		uint32_t address, uint32_t size, uint32_t *blank);
 int target_wait_state(struct target *target, enum target_state state, int ms);
 
+/**
+ * Obtain file-I/O information from target for GDB to do syscall.
+ *
+ * This routine is a wrapper for target->type->get_gdb_fileio_info.
+ */
+int target_get_gdb_fileio_info(struct target *target, struct gdb_fileio_info *fileio_info);
+
+/**
+ * Pass GDB file-I/O response to target after finishing host syscall.
+ *
+ * This routine is a wrapper for target->type->gdb_fileio_end.
+ */
+int target_gdb_fileio_end(struct target *target, int retcode, int fileio_errno, bool ctrl_c);
+
+
+
 /** Return the *name* of this targets current state */
 const char *target_state_name(struct target *target);
 
diff --git a/src/target/target_type.h b/src/target/target_type.h
index 0b8d5da..21439b6 100644
--- a/src/target/target_type.h
+++ b/src/target/target_type.h
@@ -264,6 +264,15 @@ struct target_type {
 	 * circumstances.
 	 */
 	int (*check_reset)(struct target *target);
+
+	/* get GDB file-I/O parameters from target
+	 */
+	int (*get_gdb_fileio_info)(struct target *target, struct gdb_fileio_info *fileio_info);
+
+	/* pass GDB file-I/O response to target
+	 */
+	int (*gdb_fileio_end)(struct target *target, int retcode, int fileio_errno, bool ctrl_c);
+
 };
 
 #endif /* TARGET_TYPE_H */