Re: remote serial protocol - gdbserver

[Andrew Cagney <ac131313@redhat.com>]

My wild guess appears to be correct ...


> (gdb) l
> 53              T_RFLG pk_rflg;
> 54              T_RVER pk_rver;
> 55
> 56              INT     err;
> 57
> 58              mmUserPrint(" Enter Root task\n");
> 59
> 60              /* o[WQ?*/
> 61              err = tk_ref_ver( &pk_rver );
> 62              if( err != E_OK)
> (gdb) n
> Sending packet: $m8c5e83d4,2#03...Ack
> Packet received: 04d1
> Sending packet: $M8c5e83d4,2:20c3#15...Ack
> Packet received: OK
> Sending packet: $s#73...Ack
> Packet received: T0510:1e845e8c;0e:1466658c;0f:da835e8c;
> Sending packet: $s#73...Ack
> Packet received: T0510:20845e8c;0e:1466658c;0f:da835e8c;
> Sending packet: $s#73...Ack
> Packet received: T0510:22845e8c;0e:1466658c;0f:da835e8c;
> Sending packet: $s#73...Ack
> Packet received: T0510:2874008c;0e:1466658c;0f:26845e8c;

I'm guessing that 2874008c is the PC in little-endian byte order.  It's 
just stepped the target into mmUserPrint.

> Sending packet: $Hg2#e1...Ack
> Packet received: OK
> Sending packet: $g#67...Ack
> Packet received:
> 000000002874008ca866658c00000000b0935e8ca866658c000000000000000000000000
> 00000000000000000000000000000000000000001466658c26845e8c2874008c00000000
> 0000008c0000000000000000000000000000006008000000000000000000000004000000
> 000000002e000000040000000000000000000000487d0000180000001600000004000000
> 040000000c00000039000000080000000300000000000000c81200000000000000000000
> 0000000004000000000000003e000000010000000000000000000000c812000030000000
> 000000000000000001000000000000004c000000

It's pulled the target's registers looking for the "link-register" which 
should contain the return address.

> Sending packet: $m0,2#fb...Ack
> ------------------------------------- <1>
> Packet received: b0935e8c
> Sending packet: $M0,2:20c3#0d...Ack

and then sets a breakpoint at that return-address.  For some reason GDB 
think's that's zero (bad packet? bad gdb?).

BTW: "b0935e8c" is a bogus return value for "$m0,2,#fb", only two bytes 
were requested but four were returned, which is wrong (at present).

Andrew


> ------------------------------------- <2>
> Packet received: OK
> Sending packet: $c#63...Ack
> Packet received: T0510:2874008c;0e:1466658c;0f:26845e8c;
> 
> Program received signal SIGTRAP, Trace/breakpoint trap.