Re: [PATCH v2 2/2] gdbstub: do not split gdb_monitor_write payload

[Damien Hedde <damien.hedde@greensocs.com>]

On 12/11/19 7:59 PM, Alex Bennée wrote:
> 
> Damien Hedde <damien.hedde@greensocs.com> writes:
> 
>> Since we can now send packets of arbitrary length:
>> simplify gdb_monitor_write() and send the whole payload
>> in one packet.
> 
> Do we know gdb won't barf on us. Does the negotiated max packet size
> only apply to data sent to the gdbserver?

Yes the negociated packet size is only about packet we can receive.
Qutoting the gdb doc:
| ‘PacketSize=bytes’
|
|    The remote stub can accept packets up to at least bytes in length.
| GDB will send packets up to this size for bulk transfers, and will
| never send larger packets.

The qSupported doc also says that "Any GDB which sends a ‘qSupported’
packet supports receiving packets of unlimited length".
I did some digging and qSupported appeared in gdb 6.6 (december 2006).
And gdb supported arbitrary sized packet even before that (6.4.9 2006 too).

> 
>>
>> Suggested-by: Luc Michel <luc.michel@greensocs.com>
>> Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
>> ---
>>  gdbstub.c | 23 +++--------------------
>>  1 file changed, 3 insertions(+), 20 deletions(-)
>>
>> diff --git a/gdbstub.c b/gdbstub.c
>> index 93b26f1b86..ef999abee2 100644
>> --- a/gdbstub.c
>> +++ b/gdbstub.c
>> @@ -3200,28 +3200,11 @@ static void gdb_chr_event(void *opaque, int event)
>>      }
>>  }
>>  
>> -static void gdb_monitor_output(GDBState *s, const char *msg, int len)
>> -{
>> -    g_autoptr(GString) buf = g_string_new("O");
>> -    memtohex(buf, (uint8_t *)msg, len);
>> -    put_packet(buf->str);
>> -}
>> -
>>  static int gdb_monitor_write(Chardev *chr, const uint8_t *buf, int len)
>>  {
>> -    const char *p = (const char *)buf;
>> -    int max_sz;
>> -
>> -    max_sz = (MAX_PACKET_LENGTH / 2) + 1;
>> -    for (;;) {
>> -        if (len <= max_sz) {
>> -            gdb_monitor_output(&gdbserver_state, p, len);
>> -            break;
>> -        }
>> -        gdb_monitor_output(&gdbserver_state, p, max_sz);
>> -        p += max_sz;
>> -        len -= max_sz;
>> -    }
>> +    g_autoptr(GString) hex_buf = g_string_new("O");
>> +    memtohex(hex_buf, buf, len);
>> +    put_packet(hex_buf->str);
>>      return len;
>>  }
> 
>