内核调试器kdb与kgdb模式相互切换

关门放代码, linux/kernel/debug/debug_core.c:  kgdb_cpu_enter()
{
...
while (1) {
/* 根据当前设定模式，选择stub */
 if (dbg_kdb_mode) {
            kgdb_connected = 1;
            error = kdb_stub(ks);
            if (error == -1)
                continue;
            kgdb_connected = 0;
        } else {
            error = gdb_serial_stub(ks);
        }
 
/* stub函数的返回值是否是切换 stub的指令 */
if (error == DBG_PASS_EVENT) {
            dbg_kdb_mode = !dbg_kdb_mode;
        }
}
...
}

继续关门放代码, linux/kernel/debug/gdbstub.c: gdb_serial_stub()
{
...
while (1) {
switch (gdb协议发送的数据) {
        case '3': /* Escape into back into kdb */
            if (remcom_in_buffer[1] == '\0') {
                gdb_cmd_detachkill(ks);
                return DBG_PASS_EVENT;
            }
}
...
}

放代码 linux/kernel/debug/kdb/kdb_main.c:
void kdb_inittab(void)
{
 kdb_register_repeat("kgdb", kdb_kgdb, "",
      "Enter kgdb mode", 0, KDB_REPEAT_NONE);
}
 
static int kdb_kgdb(int argc, const char **argv)
{
    return KDB_CMD_KGDB;
}
 
linux/kernel/debug/kdb/kdb_debugger.c:
int kdb_stub()
{
  if (error == KDB_CMD_KGDB) {
        if (KDB_STATE(DOING_KGDB) || KDB_STATE(DOING_KGDB2)) {
    /*
     * This inteface glue which allows kdb to transition in into
     * the gdb stub.  In order to do this the '?' or '' gdb serial
     * packet response is processed here.  And then control is
     * passed to the gdbstub.
     */
            if (KDB_STATE(DOING_KGDB))
                gdbstub_state(ks, "?");
            else
                gdbstub_state(ks, "");
            KDB_STATE_CLEAR(DOING_KGDB);
            KDB_STATE_CLEAR(DOING_KGDB2);
        }
        return DBG_PASS_EVENT;
    }
}

放gdb的代码
gdb/gdb/remote.c: remote_start_remote()
{
if (interrupt_on_connect)
    send_interrupt_sequence ();
 
  /* The first packet we send to the target is the optional "supported
     packets" request.  If the target can answer this, it will tell us
     which later probes to skip.  */
remote_query_supported ();
...
}
 
void remote_query_supported ()
{
 /* The packet support flags are handled differently for this packet
     than for most others.  We treat an error, a disabled packet, and
     an empty response identically: any features which must be reported
     to be used will be automatically disabled.  An empty buffer
     accomplishes this, since that is also the representation for a list
     containing no features.  */
 
  rs->buf[0] = 0;
  if (remote_protocol_packets[PACKET_qSupported].support != PACKET_DISABLE)
    {
      char *q = NULL;
      struct cleanup *old_chain = make_cleanup (free_current_contents, &q);
 
      if (rs->extended)
    q = remote_query_supported_append (q, "multiprocess+");
 
      if (remote_support_xml)
    q = remote_query_supported_append (q, remote_support_xml);
 
      q = remote_query_supported_append (q, "qRelocInsn+");
 
      q = reconcat (q, "qSupported:", q, (char *) NULL);
      putpkt (q);
}

1) $qSupported:xmlRegisters=i386;qRelocInsn+#25
2) $qSupported:qRelocInsn+#9a
3) $qSupported#37

关门放kdb处理代码: linux/kernel/debug/kdb/kdb_io.c:  char* kdb_read()
{
 
 /* Special escape to kgdb */
            if (lastchar - buffer >= 5 &&
                strcmp(lastchar - 5, "$?#3f") == 0) {
                strcpy(buffer, "kgdb");
                KDB_STATE_SET(DOING_KGDB);
                return buffer;
            }
            if (lastchar - buffer >= 11 &&
                strcmp(lastchar - 11, "$qSupported") == 0) {
                strcpy(buffer, "kgdb");
                KDB_STATE_SET(DOING_KGDB2);
                return buffer;
            }
}