gdbstub: implement remote debugging protocol escapes for command receive
- decode escape sequences
- decompress run-length encoding escape sequences
- report command parsing problems to output when debug output is enabled
- reject packet checksums that are not valid hex digits
- compute the checksum based on the packet stream, not based on the
decoded packet
Tested with GDB and QtCreator integrated debugger on SMP QEMU instance.
Works for me.
Signed-off-by: Doug Gale <doug16k@gmail.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/gdbstub.c b/gdbstub.c
index 07ebfe9..86eed4f 100644
--- a/gdbstub.c
+++ b/gdbstub.c
@@ -286,6 +286,8 @@
RS_INACTIVE,
RS_IDLE,
RS_GETLINE,
+ RS_GETLINE_ESC,
+ RS_GETLINE_RLE,
RS_CHKSUM1,
RS_CHKSUM2,
};
@@ -296,7 +298,8 @@
enum RSState state; /* parsing state */
char line_buf[MAX_PACKET_LENGTH];
int line_buf_index;
- int line_csum;
+ int line_sum; /* running checksum */
+ int line_csum; /* checksum at the end of the packet */
uint8_t last_packet[MAX_PACKET_LENGTH + 4];
int last_packet_len;
int signal;
@@ -1508,7 +1511,6 @@
static void gdb_read_byte(GDBState *s, int ch)
{
- int i, csum;
uint8_t reply;
#ifndef CONFIG_USER_ONLY
@@ -1542,35 +1544,123 @@
switch(s->state) {
case RS_IDLE:
if (ch == '$') {
+ /* start of command packet */
s->line_buf_index = 0;
+ s->line_sum = 0;
s->state = RS_GETLINE;
+ } else {
+#ifdef DEBUG_GDB
+ printf("gdbstub received garbage between packets: 0x%x\n", ch);
+#endif
}
break;
case RS_GETLINE:
- if (ch == '#') {
- s->state = RS_CHKSUM1;
+ if (ch == '}') {
+ /* start escape sequence */
+ s->state = RS_GETLINE_ESC;
+ s->line_sum += ch;
+ } else if (ch == '*') {
+ /* start run length encoding sequence */
+ s->state = RS_GETLINE_RLE;
+ s->line_sum += ch;
+ } else if (ch == '#') {
+ /* end of command, start of checksum*/
+ s->state = RS_CHKSUM1;
} else if (s->line_buf_index >= sizeof(s->line_buf) - 1) {
+#ifdef DEBUG_GDB
+ printf("gdbstub command buffer overrun, dropping command\n");
+#endif
s->state = RS_IDLE;
} else {
- s->line_buf[s->line_buf_index++] = ch;
+ /* unescaped command character */
+ s->line_buf[s->line_buf_index++] = ch;
+ s->line_sum += ch;
+ }
+ break;
+ case RS_GETLINE_ESC:
+ if (ch == '#') {
+ /* unexpected end of command in escape sequence */
+ s->state = RS_CHKSUM1;
+ } else if (s->line_buf_index >= sizeof(s->line_buf) - 1) {
+ /* command buffer overrun */
+#ifdef DEBUG_GDB
+ printf("gdbstub command buffer overrun, dropping command\n");
+#endif
+ s->state = RS_IDLE;
+ } else {
+ /* parse escaped character and leave escape state */
+ s->line_buf[s->line_buf_index++] = ch ^ 0x20;
+ s->line_sum += ch;
+ s->state = RS_GETLINE;
+ }
+ break;
+ case RS_GETLINE_RLE:
+ if (ch < ' ') {
+ /* invalid RLE count encoding */
+#ifdef DEBUG_GDB
+ printf("gdbstub got invalid RLE count: 0x%x\n", ch);
+#endif
+ s->state = RS_GETLINE;
+ } else {
+ /* decode repeat length */
+ int repeat = (unsigned char)ch - ' ' + 3;
+ if (s->line_buf_index + repeat >= sizeof(s->line_buf) - 1) {
+ /* that many repeats would overrun the command buffer */
+#ifdef DEBUG_GDB
+ printf("gdbstub command buffer overrun,"
+ " dropping command\n");
+#endif
+ s->state = RS_IDLE;
+ } else if (s->line_buf_index < 1) {
+ /* got a repeat but we have nothing to repeat */
+#ifdef DEBUG_GDB
+ printf("gdbstub got invalid RLE sequence\n");
+#endif
+ s->state = RS_GETLINE;
+ } else {
+ /* repeat the last character */
+ memset(s->line_buf + s->line_buf_index,
+ s->line_buf[s->line_buf_index - 1], repeat);
+ s->line_buf_index += repeat;
+ s->line_sum += ch;
+ s->state = RS_GETLINE;
+ }
}
break;
case RS_CHKSUM1:
+ /* get high hex digit of checksum */
+ if (!isxdigit(ch)) {
+#ifdef DEBUG_GDB
+ printf("gdbstub got invalid command checksum digit\n");
+#endif
+ s->state = RS_GETLINE;
+ break;
+ }
s->line_buf[s->line_buf_index] = '\0';
s->line_csum = fromhex(ch) << 4;
s->state = RS_CHKSUM2;
break;
case RS_CHKSUM2:
- s->line_csum |= fromhex(ch);
- csum = 0;
- for(i = 0; i < s->line_buf_index; i++) {
- csum += s->line_buf[i];
+ /* get low hex digit of checksum */
+ if (!isxdigit(ch)) {
+#ifdef DEBUG_GDB
+ printf("gdbstub got invalid command checksum digit\n");
+#endif
+ s->state = RS_GETLINE;
+ break;
}
- if (s->line_csum != (csum & 0xff)) {
+ s->line_csum |= fromhex(ch);
+
+ if (s->line_csum != (s->line_sum & 0xff)) {
+ /* send NAK reply */
reply = '-';
put_buffer(s, &reply, 1);
+#ifdef DEBUG_GDB
+ printf("gdbstub got command packet with incorrect checksum\n");
+#endif
s->state = RS_IDLE;
} else {
+ /* send ACK reply */
reply = '+';
put_buffer(s, &reply, 1);
s->state = gdb_handle_packet(s, s->line_buf);
