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From: Stefan Hajnoczi <stefanha@gmail.com>
Date: Mon, 8 May 2017 10:01:10 +0100
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Subject: Re: [Qemu-devel] [PATCH] gdbstub: implement remote debugging
 protocol escapes for command receive
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To: Doug Gale <doug16k@gmail.com>
Cc: qemu-devel <qemu-devel@nongnu.org>

On Sun, May 7, 2017 at 4:26 PM, Doug Gale <doug16k@gmail.com> wrote:
> On Fri, May 5, 2017 at 10:45 AM, Stefan Hajnoczi <stefanha@gmail.com> wrote:
>> On Tue, May 02, 2017 at 10:32:40AM -0400, Doug Gale wrote:
>>> +            } 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 <= 2) {
>>
>> Why s->line_buf_index <= 2?  I expected s->line_buf_index < 1 since we
>> just need 1 character to clone for run-length decoding.
>
> Yes, on second thought, <= 2 is off by one. [0] would be the '$', [1]
> would be the repeated character, and [2] would be the '*'.

'$' and '*' are not placed into line_buf[] and do not increment
line_buf_index.  They don't count.

I think the correct condition is line_buf_index < 1 so that the
following input from the GDB documentation parses: "$0* " -> "0000".

https://sourceware.org/gdb/onlinedocs/gdb/Overview.html