new gdb remote packet type

Robert Picco
2004-04-16T00:45:05Z

Hi:

I encountered an issue when attempting to get the kernel debugger (kgdb) running for IA64 on Linux.
The debugger works fine over ethernet but won't work over a serial line
because of the size of the g-packet (>10K bytes). Most registers in the
g-packet aren't required for kernel debugging. The patch below
has introduced a new gdb packet which asks the target (kgdb) for the
register offsets in the g-packet. In my kernel kgdb stub all stacked
registers, nearly all floating point (kernel uses small subset of
floating point), all predicate registers, all nat registers and most of
the application registers are excluded. The patch won't break any
existing targets of gdb because the new packet won't be recognized. No other
architectures (at least those I'm aware of) suffer from such a huge
g-packet.

Do you think a solution like this is possible for inclusion into gdb?

thanks,

Bob

--- gdb-6.0-orig/gdb/remote.c 2003-06-30 11:51:49.000000000 -0400
+++ gdb-6.0/gdb/remote.c 2004-04-13 11:46:38.000000000 -0400
@@ -2131,6 +2131,44 @@
return 1;
}

+static int register_init;
+
+static void
+remote_register_size(void)
+{
+ struct remote_state *rs = get_remote_state ();
+ char *buf = alloca (rs->remote_packet_size);
+ int regnum, offset, size;
+
+
+ register_init = 1;
+
+ for (size = 0, regnum = 0; regnum < NUM_REGS + NUM_PSEUDO_REGS; regnum++)
+ {
+ struct packet_reg *r = &rs->regs[regnum];
+ buf[0] = 'r';
+ bin2hex ((char *) &regnum, &buf[1], sizeof(regnum));
+ putpkt(buf);
+ getpkt (buf, (rs->remote_packet_size), 0);
+ if (buf[0] != 'r') {
+ if (regnum)
+ fprintf_unfiltered (gdb_stdlog,
+ "Received some valid register packets and later failed\n");
+ return;
+ }
+ hex2bin(&buf[1], (char *)&offset, sizeof(offset));
+ r->offset = offset;
+ if (offset != -1) {
+ r->in_g_packet = 1;
+ size += register_size (current_gdbarch, regnum);
+ }
+ else
+ r->in_g_packet = 0;
+
+ }
+ rs->sizeof_g_packet = size;
+}
+
static int
remote_start_remote (struct ui_out *uiout, void *dummy)
{
@@ -2139,9 +2177,13 @@
/* Ack any packet which the remote side has already sent. */
serial_write (remote_desc, "+", 1);

+
/* Let the stub know that we want it to return the thread. */
set_thread (-1, 0);

+ if (!register_init)
+ remote_register_size();
+
inferior_ptid = remote_current_thread (inferior_ptid);

get_offsets (); /* Get text, data & bss offsets */
@@ -3438,8 +3480,8 @@
gdb_assert (reg != NULL);
if (!reg->in_g_packet)
internal_error (__FILE__, __LINE__,
- "Attempt to fetch a non G-packet register when this "
- "remote.c does not support the p-packet.");
+ "Attempt to fetch a non G-packet register (%d) when this "
+ "remote.c does not support the p-packet.", regnum);
}

sprintf (buf, "g");