Fix remote 'g' command error handling (PR remote/9665)

'g' command returns hex-string as response so simply checking for 'E'
to determine if it failed is not enough and can trigger spurious error
messages.  For example, invalid behaviour can be easily triggered on
Cortex-M as follows:

  (gdb) set $r0 = 0xe0
  Sending packet: $P0=e0000000#72...Packet received: OK
  Packet P (set-register) is supported
  Sending packet: $g#67...Packet received: E0000000849A0020...
  Remote failure reply: E0000000849A0020...

This patch fixes the problem by calling putpkt()/getpkt() directly and
checking result with packet_check_result().  This works fine since Enn
response has odd number of bytes while proper response has even number
of bytes.

Also, remote_send() is now not used anywhere so it can be removed.

gdb/Changelog:
2018-04-26  Andrzej Kaczmarek  <andrzej.kaczmarek@codecoup.pl>

	PR remote/9665
	* remote.c (send_g_packet): Use putpkt/getpkt/packet_check_result
	instead of remote_send.
	(remote_send): Remove.

1 files changed, 5 insertions, 19 deletions

diff --git a/gdb/remote.c b/gdb/remote.c
index 193037b..5920b82 100644
--- a/gdb/remote.c
+++ b/gdb/remote.c
@@ -122,8 +122,6 @@ static void remote_mourn (struct target_ops *ops);
 
 static void extended_remote_restart (void);
 
-static void remote_send (char **buf, long *sizeof_buf_p);
-
 static int readchar (int timeout);
 
 static void remote_serial_write (const char *str, int len);
@@ -7524,7 +7522,11 @@ send_g_packet (void)
   int buf_len;
 
   xsnprintf (rs->buf, get_remote_packet_size (), "g");
-  remote_send (&rs->buf, &rs->buf_size);
+  putpkt (rs->buf);
+  getpkt (&rs->buf, &rs->buf_size, 0);
+  if (packet_check_result (rs->buf) == PACKET_ERROR)
+    error (_("Could not read registers; remote failure reply '%s'"),
+           rs->buf);
 
   /* We can get out of synch in various cases.  If the first character
      in the buffer is not a hex character, assume that has happened
@@ -8600,22 +8602,6 @@ remote_serial_write (const char *str, int len)
     set_quit_flag ();
 }
 
-/* Send the command in *BUF to the remote machine, and read the reply
-   into *BUF.  Report an error if we get an error reply.  Resize
-   *BUF using xrealloc if necessary to hold the result, and update
-   *SIZEOF_BUF.  */
-
-static void
-remote_send (char **buf,
-	     long *sizeof_buf)
-{
-  putpkt (*buf);
-  getpkt (buf, sizeof_buf, 0);
-
-  if ((*buf)[0] == 'E')
-    error (_("Remote failure reply: %s"), *buf);
-}
-
 /* Return a string representing an escaped version of BUF, of len N.
    E.g. \n is converted to \\n, \t to \\t, etc.  */