Re: [RFA] Fix buffer full test in remote.c

[Andrew Cagney <ac131313 at cygnus dot com>]

> To check when were are close to filling the buffer, we need to use the
> size of the allocated buffer, not the available buffer space after
> subtracting off all the packet overhead.
> 
> Consider the case where get_memory_write_packet_size() returns 16.
> The allocated buffer will be 17 bytes.  The X packet header will
> actually be around 9 bytes, which is subtracted from 16 to give 7
> bytes available for data.  The loop will never execute because "p-buf"
> will be 9 after putting the header in the buf, and "max_buf_size-2"
> will be 7-2, or 5, and 9 is not less than 5.  (These numbers may not
> be exact, but should point out the problem).

Ah!  I don't think changing the test to use sizeof_buf (sizeof_buf - 2) 
is correct.  That will let GDB send down packets of size:

	sizeof_buf - 2 + strlen ("#NN")

which I think overflows the max packet size (looking at my hand sketch, 
by one character?).

I suspect a better way of fixing it is to change things to:

	/* Subtract header overhead ... */
	payload_size = max_buf_size - (...);
	....
	s/max_buf_size/payload_size/
	....
	/* Append the packet body.  */
	payload_start = p;

	..... && (p - payload_start) < payload_size);


(if nothing else it gets rid of the overloaded use of max_buf_size).

Andrew