gdbstub/user.c - qemu - Git at Google

 /*
  * gdbstub user-mode helper routines.
  *
  * We know for user-mode we are using TCG so we can call stuff directly.
  *
  * Copyright (c) 2003-2005 Fabrice Bellard
  * Copyright (c) 2022 Linaro Ltd
  *
  * SPDX-License-Identifier: LGPL-2.0+
  */

 #include "qemu/osdep.h"
 #include "qemu/cutils.h"
 #include "qemu/sockets.h"
 #include "exec/hwaddr.h"
 #include "exec/tb-flush.h"
 #include "exec/gdbstub.h"
 #include "gdbstub/syscalls.h"
 #include "gdbstub/user.h"
 #include "hw/core/cpu.h"
 #include "trace.h"
 #include "internals.h"

 /* User-mode specific state */
 typedef struct {
     int fd;
     char *socket_path;
     int running_state;
 } GDBUserState;

 static GDBUserState gdbserver_user_state;

 int gdb_get_char(void)
 {
     uint8_t ch;
     int ret;

     for (;;) {
         ret = recv(gdbserver_user_state.fd, &ch, 1, 0);
         if (ret < 0) {
             if (errno == ECONNRESET) {
                 gdbserver_user_state.fd = -1;
             }
             if (errno != EINTR) {
                 return -1;
             }
         } else if (ret == 0) {
             close(gdbserver_user_state.fd);
             gdbserver_user_state.fd = -1;
             return -1;
         } else {
             break;
         }
     }
     return ch;
 }

 bool gdb_got_immediate_ack(void)
 {
     int i;

     i = gdb_get_char();
     if (i < 0) {
         /* no response, continue anyway */
         return true;
     }

     if (i == '+') {
         /* received correctly, continue */
         return true;
     }

     /* anything else, including '-' then try again */
     return false;
 }

 void gdb_put_buffer(const uint8_t *buf, int len)
 {
     int ret;

     while (len > 0) {
         ret = send(gdbserver_user_state.fd, buf, len, 0);
         if (ret < 0) {
             if (errno != EINTR) {
                 return;
             }
         } else {
             buf += ret;
             len -= ret;
         }
     }
 }

 /* Tell the remote gdb that the process has exited.  */
 void gdb_exit(int code)
 {
     char buf[4];

     if (!gdbserver_state.init) {
         return;
     }
     if (gdbserver_user_state.socket_path) {
         unlink(gdbserver_user_state.socket_path);
     }
     if (gdbserver_user_state.fd < 0) {
         return;
     }

     trace_gdbstub_op_exiting((uint8_t)code);

     if (gdbserver_state.allow_stop_reply) {
         snprintf(buf, sizeof(buf), "W%02x", (uint8_t)code);
         gdb_put_packet(buf);
         gdbserver_state.allow_stop_reply = false;
     }
 }

 int gdb_handlesig(CPUState *cpu, int sig)
 {
     char buf[256];
     int n;

     if (!gdbserver_state.init || gdbserver_user_state.fd < 0) {
         return sig;
     }

     /* disable single step if it was enabled */
     cpu_single_step(cpu, 0);
     tb_flush(cpu);

     if (sig != 0) {
         gdb_set_stop_cpu(cpu);
         if (gdbserver_state.allow_stop_reply) {
             g_string_printf(gdbserver_state.str_buf,
                             "T%02xthread:", gdb_target_signal_to_gdb(sig));
             gdb_append_thread_id(cpu, gdbserver_state.str_buf);
             g_string_append_c(gdbserver_state.str_buf, ';');
             gdb_put_strbuf();
             gdbserver_state.allow_stop_reply = false;
         }
     }
     /*
      * gdb_put_packet() might have detected that the peer terminated the
      * connection.
      */
     if (gdbserver_user_state.fd < 0) {
         return sig;
     }

     sig = 0;
     gdbserver_state.state = RS_IDLE;
     gdbserver_user_state.running_state = 0;
     while (gdbserver_user_state.running_state == 0) {
         n = read(gdbserver_user_state.fd, buf, 256);
         if (n > 0) {
             int i;

             for (i = 0; i < n; i++) {
                 gdb_read_byte(buf[i]);
             }
         } else {
             /*
              * XXX: Connection closed.  Should probably wait for another
              * connection before continuing.
              */
             if (n == 0) {
                 close(gdbserver_user_state.fd);
             }
             gdbserver_user_state.fd = -1;
             return sig;
         }
     }
     sig = gdbserver_state.signal;
     gdbserver_state.signal = 0;
     return sig;
 }

 /* Tell the remote gdb that the process has exited due to SIG.  */
 void gdb_signalled(CPUArchState *env, int sig)
 {
     char buf[4];

     if (!gdbserver_state.init || gdbserver_user_state.fd < 0 ||
         !gdbserver_state.allow_stop_reply) {
         return;
     }

     snprintf(buf, sizeof(buf), "X%02x", gdb_target_signal_to_gdb(sig));
     gdb_put_packet(buf);
     gdbserver_state.allow_stop_reply = false;
 }

 static void gdb_accept_init(int fd)
 {
     gdb_init_gdbserver_state();
     gdb_create_default_process(&gdbserver_state);
     gdbserver_state.processes[0].attached = true;
     gdbserver_state.c_cpu = gdb_first_attached_cpu();
     gdbserver_state.g_cpu = gdbserver_state.c_cpu;
     gdbserver_user_state.fd = fd;
 }

 static bool gdb_accept_socket(int gdb_fd)
 {
     int fd;

     for (;;) {
         fd = accept(gdb_fd, NULL, NULL);
         if (fd < 0 && errno != EINTR) {
             perror("accept socket");
             return false;
         } else if (fd >= 0) {
             qemu_set_cloexec(fd);
             break;
         }
     }

     gdb_accept_init(fd);
     return true;
 }

 static int gdbserver_open_socket(const char *path)
 {
     struct sockaddr_un sockaddr = {};
     int fd, ret;

     fd = socket(AF_UNIX, SOCK_STREAM, 0);
     if (fd < 0) {
         perror("create socket");
         return -1;
     }

     sockaddr.sun_family = AF_UNIX;
     pstrcpy(sockaddr.sun_path, sizeof(sockaddr.sun_path) - 1, path);
     ret = bind(fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr));
     if (ret < 0) {
         perror("bind socket");
         close(fd);
         return -1;
     }
     ret = listen(fd, 1);
     if (ret < 0) {
         perror("listen socket");
         close(fd);
         return -1;
     }

     return fd;
 }

 static bool gdb_accept_tcp(int gdb_fd)
 {
     struct sockaddr_in sockaddr = {};
     socklen_t len;
     int fd;

     for (;;) {
         len = sizeof(sockaddr);
         fd = accept(gdb_fd, (struct sockaddr *)&sockaddr, &len);
         if (fd < 0 && errno != EINTR) {
             perror("accept");
             return false;
         } else if (fd >= 0) {
             qemu_set_cloexec(fd);
             break;
         }
     }

     /* set short latency */
     if (socket_set_nodelay(fd)) {
         perror("setsockopt");
         close(fd);
         return false;
     }

     gdb_accept_init(fd);
     return true;
 }

 static int gdbserver_open_port(int port)
 {
     struct sockaddr_in sockaddr;
     int fd, ret;

     fd = socket(PF_INET, SOCK_STREAM, 0);
     if (fd < 0) {
         perror("socket");
         return -1;
     }
     qemu_set_cloexec(fd);

     socket_set_fast_reuse(fd);

     sockaddr.sin_family = AF_INET;
     sockaddr.sin_port = htons(port);
     sockaddr.sin_addr.s_addr = 0;
     ret = bind(fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr));
     if (ret < 0) {
         perror("bind");
         close(fd);
         return -1;
     }
     ret = listen(fd, 1);
     if (ret < 0) {
         perror("listen");
         close(fd);
         return -1;
     }

     return fd;
 }

 int gdbserver_start(const char *port_or_path)
 {
     int port = g_ascii_strtoull(port_or_path, NULL, 10);
     int gdb_fd;

     if (port > 0) {
         gdb_fd = gdbserver_open_port(port);
     } else {
         gdb_fd = gdbserver_open_socket(port_or_path);
     }

     if (gdb_fd < 0) {
         return -1;
     }

     if (port > 0 && gdb_accept_tcp(gdb_fd)) {
         return 0;
     } else if (gdb_accept_socket(gdb_fd)) {
         gdbserver_user_state.socket_path = g_strdup(port_or_path);
         return 0;
     }

     /* gone wrong */
     close(gdb_fd);
     return -1;
 }

 /* Disable gdb stub for child processes.  */
 void gdbserver_fork(CPUState *cpu)
 {
     if (!gdbserver_state.init || gdbserver_user_state.fd < 0) {
         return;
     }
     close(gdbserver_user_state.fd);
     gdbserver_user_state.fd = -1;
     cpu_breakpoint_remove_all(cpu, BP_GDB);
     /* no cpu_watchpoint_remove_all for user-mode */
 }

 /*
  * Execution state helpers
  */

 void gdb_handle_query_attached(GArray *params, void *user_ctx)
 {
     gdb_put_packet("0");
 }

 void gdb_continue(void)
 {
     gdbserver_user_state.running_state = 1;
     trace_gdbstub_op_continue();
 }

 /*
  * Resume execution, for user-mode emulation it's equivalent to
  * gdb_continue.
  */
 int gdb_continue_partial(char *newstates)
 {
     CPUState *cpu;
     int res = 0;
     /*
      * This is not exactly accurate, but it's an improvement compared to the
      * previous situation, where only one CPU would be single-stepped.
      */
     CPU_FOREACH(cpu) {
         if (newstates[cpu->cpu_index] == 's') {
             trace_gdbstub_op_stepping(cpu->cpu_index);
             cpu_single_step(cpu, gdbserver_state.sstep_flags);
         }
     }
     gdbserver_user_state.running_state = 1;
     return res;
 }

 /*
  * Memory access helpers
  */
 int gdb_target_memory_rw_debug(CPUState *cpu, hwaddr addr,
                                uint8_t *buf, int len, bool is_write)
 {
     CPUClass *cc;

     cc = CPU_GET_CLASS(cpu);
     if (cc->memory_rw_debug) {
         return cc->memory_rw_debug(cpu, addr, buf, len, is_write);
     }
     return cpu_memory_rw_debug(cpu, addr, buf, len, is_write);
 }

 /*
  * cpu helpers
  */

 unsigned int gdb_get_max_cpus(void)
 {
     CPUState *cpu;
     unsigned int max_cpus = 1;

     CPU_FOREACH(cpu) {
         max_cpus = max_cpus <= cpu->cpu_index ? cpu->cpu_index + 1 : max_cpus;
     }

     return max_cpus;
 }

 /* replay not supported for user-mode */
 bool gdb_can_reverse(void)
 {
     return false;
 }

 /*
  * Break/Watch point helpers
  */

 bool gdb_supports_guest_debug(void)
 {
     /* user-mode == TCG == supported */
     return true;
 }

 int gdb_breakpoint_insert(CPUState *cs, int type, vaddr addr, vaddr len)
 {
     CPUState *cpu;
     int err = 0;

     switch (type) {
     case GDB_BREAKPOINT_SW:
     case GDB_BREAKPOINT_HW:
         CPU_FOREACH(cpu) {
             err = cpu_breakpoint_insert(cpu, addr, BP_GDB, NULL);
             if (err) {
                 break;
             }
         }
         return err;
     default:
         /* user-mode doesn't support watchpoints */
         return -ENOSYS;
     }
 }

 int gdb_breakpoint_remove(CPUState *cs, int type, vaddr addr, vaddr len)
 {
     CPUState *cpu;
     int err = 0;

     switch (type) {
     case GDB_BREAKPOINT_SW:
     case GDB_BREAKPOINT_HW:
         CPU_FOREACH(cpu) {
             err = cpu_breakpoint_remove(cpu, addr, BP_GDB);
             if (err) {
                 break;
             }
         }
         return err;
     default:
         /* user-mode doesn't support watchpoints */
         return -ENOSYS;
     }
 }

 void gdb_breakpoint_remove_all(CPUState *cs)
 {
     cpu_breakpoint_remove_all(cs, BP_GDB);
 }

 /*
  * For user-mode syscall support we send the system call immediately
  * and then return control to gdb for it to process the syscall request.
  * Since the protocol requires that gdb hands control back to us
  * using a "here are the results" F packet, we don't need to check
  * gdb_handlesig's return value (which is the signal to deliver if
  * execution was resumed via a continue packet).
  */
 void gdb_syscall_handling(const char *syscall_packet)
 {
     gdb_put_packet(syscall_packet);
     gdb_handlesig(gdbserver_state.c_cpu, 0);
 }
	/*
	* gdbstub user-mode helper routines.
	*
	* We know for user-mode we are using TCG so we can call stuff directly.
	*
	* Copyright (c) 2003-2005 Fabrice Bellard
	* Copyright (c) 2022 Linaro Ltd
	*
	* SPDX-License-Identifier: LGPL-2.0+
	*/

	#include "qemu/osdep.h"
	#include "qemu/cutils.h"
	#include "qemu/sockets.h"
	#include "exec/hwaddr.h"
	#include "exec/tb-flush.h"
	#include "exec/gdbstub.h"
	#include "gdbstub/syscalls.h"
	#include "gdbstub/user.h"
	#include "hw/core/cpu.h"
	#include "trace.h"
	#include "internals.h"

	/* User-mode specific state */
	typedef struct {
	int fd;
	char *socket_path;
	int running_state;
	} GDBUserState;

	static GDBUserState gdbserver_user_state;

	int gdb_get_char(void)
	{
	uint8_t ch;
	int ret;

	for (;;) {
	ret = recv(gdbserver_user_state.fd, &ch, 1, 0);
	if (ret < 0) {
	if (errno == ECONNRESET) {
	gdbserver_user_state.fd = -1;
	}
	if (errno != EINTR) {
	return -1;
	}
	} else if (ret == 0) {
	close(gdbserver_user_state.fd);
	gdbserver_user_state.fd = -1;
	return -1;
	} else {
	break;
	}
	}
	return ch;
	}

	bool gdb_got_immediate_ack(void)
	{
	int i;

	i = gdb_get_char();
	if (i < 0) {
	/* no response, continue anyway */
	return true;
	}

	if (i == '+') {
	/* received correctly, continue */
	return true;
	}

	/* anything else, including '-' then try again */
	return false;
	}

	void gdb_put_buffer(const uint8_t *buf, int len)
	{
	int ret;

	while (len > 0) {
	ret = send(gdbserver_user_state.fd, buf, len, 0);
	if (ret < 0) {
	if (errno != EINTR) {
	return;
	}
	} else {
	buf += ret;
	len -= ret;
	}
	}
	}

	/* Tell the remote gdb that the process has exited. */
	void gdb_exit(int code)
	{
	char buf[4];

	if (!gdbserver_state.init) {
	return;
	}
	if (gdbserver_user_state.socket_path) {
	unlink(gdbserver_user_state.socket_path);
	}
	if (gdbserver_user_state.fd < 0) {
	return;
	}

	trace_gdbstub_op_exiting((uint8_t)code);

	if (gdbserver_state.allow_stop_reply) {
	snprintf(buf, sizeof(buf), "W%02x", (uint8_t)code);
	gdb_put_packet(buf);
	gdbserver_state.allow_stop_reply = false;
	}
	}

	int gdb_handlesig(CPUState *cpu, int sig)
	{
	char buf[256];
	int n;

	if (!gdbserver_state.init \|\| gdbserver_user_state.fd < 0) {
	return sig;
	}

	/* disable single step if it was enabled */
	cpu_single_step(cpu, 0);
	tb_flush(cpu);

	if (sig != 0) {
	gdb_set_stop_cpu(cpu);
	if (gdbserver_state.allow_stop_reply) {
	g_string_printf(gdbserver_state.str_buf,
	"T%02xthread:", gdb_target_signal_to_gdb(sig));
	gdb_append_thread_id(cpu, gdbserver_state.str_buf);
	g_string_append_c(gdbserver_state.str_buf, ';');
	gdb_put_strbuf();
	gdbserver_state.allow_stop_reply = false;
	}
	}
	/*
	* gdb_put_packet() might have detected that the peer terminated the
	* connection.
	*/
	if (gdbserver_user_state.fd < 0) {
	return sig;
	}

	sig = 0;
	gdbserver_state.state = RS_IDLE;
	gdbserver_user_state.running_state = 0;
	while (gdbserver_user_state.running_state == 0) {
	n = read(gdbserver_user_state.fd, buf, 256);
	if (n > 0) {
	int i;

	for (i = 0; i < n; i++) {
	gdb_read_byte(buf[i]);
	}
	} else {
	/*
	* XXX: Connection closed. Should probably wait for another
	* connection before continuing.
	*/
	if (n == 0) {
	close(gdbserver_user_state.fd);
	}
	gdbserver_user_state.fd = -1;
	return sig;
	}
	}
	sig = gdbserver_state.signal;
	gdbserver_state.signal = 0;
	return sig;
	}

	/* Tell the remote gdb that the process has exited due to SIG. */
	void gdb_signalled(CPUArchState *env, int sig)
	{
	char buf[4];

	if (!gdbserver_state.init \|\| gdbserver_user_state.fd < 0 \|\|
	!gdbserver_state.allow_stop_reply) {
	return;
	}

	snprintf(buf, sizeof(buf), "X%02x", gdb_target_signal_to_gdb(sig));
	gdb_put_packet(buf);
	gdbserver_state.allow_stop_reply = false;
	}

	static void gdb_accept_init(int fd)
	{
	gdb_init_gdbserver_state();
	gdb_create_default_process(&gdbserver_state);
	gdbserver_state.processes[0].attached = true;
	gdbserver_state.c_cpu = gdb_first_attached_cpu();
	gdbserver_state.g_cpu = gdbserver_state.c_cpu;
	gdbserver_user_state.fd = fd;
	}

	static bool gdb_accept_socket(int gdb_fd)
	{
	int fd;

	for (;;) {
	fd = accept(gdb_fd, NULL, NULL);
	if (fd < 0 && errno != EINTR) {
	perror("accept socket");
	return false;
	} else if (fd >= 0) {
	qemu_set_cloexec(fd);
	break;
	}
	}

	gdb_accept_init(fd);
	return true;
	}

	static int gdbserver_open_socket(const char *path)
	{
	struct sockaddr_un sockaddr = {};
	int fd, ret;

	fd = socket(AF_UNIX, SOCK_STREAM, 0);
	if (fd < 0) {
	perror("create socket");
	return -1;
	}

	sockaddr.sun_family = AF_UNIX;
	pstrcpy(sockaddr.sun_path, sizeof(sockaddr.sun_path) - 1, path);
	ret = bind(fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr));
	if (ret < 0) {
	perror("bind socket");
	close(fd);
	return -1;
	}
	ret = listen(fd, 1);
	if (ret < 0) {
	perror("listen socket");
	close(fd);
	return -1;
	}

	return fd;
	}

	static bool gdb_accept_tcp(int gdb_fd)
	{
	struct sockaddr_in sockaddr = {};
	socklen_t len;
	int fd;

	for (;;) {
	len = sizeof(sockaddr);
	fd = accept(gdb_fd, (struct sockaddr *)&sockaddr, &len);
	if (fd < 0 && errno != EINTR) {
	perror("accept");
	return false;
	} else if (fd >= 0) {
	qemu_set_cloexec(fd);
	break;
	}
	}

	/* set short latency */
	if (socket_set_nodelay(fd)) {
	perror("setsockopt");
	close(fd);
	return false;
	}

	gdb_accept_init(fd);
	return true;
	}

	static int gdbserver_open_port(int port)
	{
	struct sockaddr_in sockaddr;
	int fd, ret;

	fd = socket(PF_INET, SOCK_STREAM, 0);
	if (fd < 0) {
	perror("socket");
	return -1;
	}
	qemu_set_cloexec(fd);

	socket_set_fast_reuse(fd);

	sockaddr.sin_family = AF_INET;
	sockaddr.sin_port = htons(port);
	sockaddr.sin_addr.s_addr = 0;
	ret = bind(fd, (struct sockaddr *)&sockaddr, sizeof(sockaddr));
	if (ret < 0) {
	perror("bind");
	close(fd);
	return -1;
	}
	ret = listen(fd, 1);
	if (ret < 0) {
	perror("listen");
	close(fd);
	return -1;
	}

	return fd;
	}

	int gdbserver_start(const char *port_or_path)
	{
	int port = g_ascii_strtoull(port_or_path, NULL, 10);
	int gdb_fd;

	if (port > 0) {
	gdb_fd = gdbserver_open_port(port);
	} else {
	gdb_fd = gdbserver_open_socket(port_or_path);
	}

	if (gdb_fd < 0) {
	return -1;
	}

	if (port > 0 && gdb_accept_tcp(gdb_fd)) {
	return 0;
	} else if (gdb_accept_socket(gdb_fd)) {
	gdbserver_user_state.socket_path = g_strdup(port_or_path);
	return 0;
	}

	/* gone wrong */
	close(gdb_fd);
	return -1;
	}

	/* Disable gdb stub for child processes. */
	void gdbserver_fork(CPUState *cpu)
	{
	if (!gdbserver_state.init \|\| gdbserver_user_state.fd < 0) {
	return;
	}
	close(gdbserver_user_state.fd);
	gdbserver_user_state.fd = -1;
	cpu_breakpoint_remove_all(cpu, BP_GDB);
	/* no cpu_watchpoint_remove_all for user-mode */
	}

	/*
	* Execution state helpers
	*/

	void gdb_handle_query_attached(GArray params, void user_ctx)
	{
	gdb_put_packet("0");
	}

	void gdb_continue(void)
	{
	gdbserver_user_state.running_state = 1;
	trace_gdbstub_op_continue();
	}

	/*
	* Resume execution, for user-mode emulation it's equivalent to
	* gdb_continue.
	*/
	int gdb_continue_partial(char *newstates)
	{
	CPUState *cpu;
	int res = 0;
	/*
	* This is not exactly accurate, but it's an improvement compared to the
	* previous situation, where only one CPU would be single-stepped.
	*/
	CPU_FOREACH(cpu) {
	if (newstates[cpu->cpu_index] == 's') {
	trace_gdbstub_op_stepping(cpu->cpu_index);
	cpu_single_step(cpu, gdbserver_state.sstep_flags);
	}
	}
	gdbserver_user_state.running_state = 1;
	return res;
	}

	/*
	* Memory access helpers
	*/
	int gdb_target_memory_rw_debug(CPUState *cpu, hwaddr addr,
	uint8_t *buf, int len, bool is_write)
	{
	CPUClass *cc;

	cc = CPU_GET_CLASS(cpu);
	if (cc->memory_rw_debug) {
	return cc->memory_rw_debug(cpu, addr, buf, len, is_write);
	}
	return cpu_memory_rw_debug(cpu, addr, buf, len, is_write);
	}

	/*
	* cpu helpers
	*/

	unsigned int gdb_get_max_cpus(void)
	{
	CPUState *cpu;
	unsigned int max_cpus = 1;

	CPU_FOREACH(cpu) {
	max_cpus = max_cpus <= cpu->cpu_index ? cpu->cpu_index + 1 : max_cpus;
	}

	return max_cpus;
	}

	/* replay not supported for user-mode */
	bool gdb_can_reverse(void)
	{
	return false;
	}

	/*
	* Break/Watch point helpers
	*/

	bool gdb_supports_guest_debug(void)
	{
	/* user-mode == TCG == supported */
	return true;
	}

	int gdb_breakpoint_insert(CPUState *cs, int type, vaddr addr, vaddr len)
	{
	CPUState *cpu;
	int err = 0;

	switch (type) {
	case GDB_BREAKPOINT_SW:
	case GDB_BREAKPOINT_HW:
	CPU_FOREACH(cpu) {
	err = cpu_breakpoint_insert(cpu, addr, BP_GDB, NULL);
	if (err) {
	break;
	}
	}
	return err;
	default:
	/* user-mode doesn't support watchpoints */
	return -ENOSYS;
	}
	}

	int gdb_breakpoint_remove(CPUState *cs, int type, vaddr addr, vaddr len)
	{
	CPUState *cpu;
	int err = 0;

	switch (type) {
	case GDB_BREAKPOINT_SW:
	case GDB_BREAKPOINT_HW:
	CPU_FOREACH(cpu) {
	err = cpu_breakpoint_remove(cpu, addr, BP_GDB);
	if (err) {
	break;
	}
	}
	return err;
	default:
	/* user-mode doesn't support watchpoints */
	return -ENOSYS;
	}
	}

	void gdb_breakpoint_remove_all(CPUState *cs)
	{
	cpu_breakpoint_remove_all(cs, BP_GDB);
	}

	/*
	* For user-mode syscall support we send the system call immediately
	* and then return control to gdb for it to process the syscall request.
	* Since the protocol requires that gdb hands control back to us
	* using a "here are the results" F packet, we don't need to check
	* gdb_handlesig's return value (which is the signal to deliver if
	* execution was resumed via a continue packet).
	*/
	void gdb_syscall_handling(const char *syscall_packet)
	{
	gdb_put_packet(syscall_packet);
	gdb_handlesig(gdbserver_state.c_cpu, 0);
	}