Re: [PATCH] gdbstub: change GDBState.last_packet to GByteArray

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

On 12/6/19 2:42 PM, Damien Hedde wrote:
> Remove the packet size upper limit by using a GByteArray
> instead of a statically allocated array for last_packet.
> Thus we can now send big packets.
> 
> Also remove the last_packet_len field and use last_packet->len
> instead.
> 
> Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>
> ---
> 
> This patch is a follow-up of Alex's series about sve registers
> which introduces some GbyteArray/Gstring in the gdbstub.
> It removes the remaining barrier to send big packets.
> 
> Based-on <20191130084602.10818-1-alex.bennee@linaro.org>
> ---
>   gdbstub.c | 39 +++++++++++++++++++++------------------
>   1 file changed, 21 insertions(+), 18 deletions(-)
> 
> diff --git a/gdbstub.c b/gdbstub.c
> index 7b695bdebe..022edd6bdb 100644
> --- a/gdbstub.c
> +++ b/gdbstub.c
> @@ -351,8 +351,7 @@ typedef struct GDBState {
>       int line_buf_index;
>       int line_sum; /* running checksum */
>       int line_csum; /* checksum at the end of the packet */
> -    uint8_t last_packet[MAX_PACKET_LENGTH + 4];
> -    int last_packet_len;
> +    GByteArray *last_packet;
>       int signal;
>   #ifdef CONFIG_USER_ONLY
>       int fd;
> @@ -384,6 +383,7 @@ static void init_gdbserver_state(void)
>       gdbserver_state.init = true;
>       gdbserver_state.str_buf = g_string_new(NULL);
>       gdbserver_state.mem_buf = g_byte_array_sized_new(MAX_PACKET_LENGTH);
> +    gdbserver_state.last_packet = g_byte_array_sized_new(MAX_PACKET_LENGTH + 4);
>   }
>   
>   #ifndef CONFIG_USER_ONLY
> @@ -626,28 +626,29 @@ static void hexdump(const char *buf, int len,
>   static int put_packet_binary(const char *buf, int len, bool dump)
>   {
>       int csum, i;
> -    uint8_t *p;
> -    uint8_t *ps = &gdbserver_state.last_packet[0];
> +    uint8_t footer[3];
>   
>       if (dump && trace_event_get_state_backends(TRACE_GDBSTUB_IO_BINARYREPLY)) {
>           hexdump(buf, len, trace_gdbstub_io_binaryreply);
>       }
>   
>       for(;;) {
> -        p = ps;
> -        *(p++) = '$';
> -        memcpy(p, buf, len);
> -        p += len;
> +        g_byte_array_set_size(gdbserver_state.last_packet, 0);
> +        g_byte_array_append(gdbserver_state.last_packet,
> +                            (const uint8_t *) "$", 1);
> +        g_byte_array_append(gdbserver_state.last_packet,
> +                            (const uint8_t *) buf, len);
>           csum = 0;
>           for(i = 0; i < len; i++) {
>               csum += buf[i];
>           }
> -        *(p++) = '#';
> -        *(p++) = tohex((csum >> 4) & 0xf);
> -        *(p++) = tohex((csum) & 0xf);
> +        footer[0] = '#';
> +        footer[1] = tohex((csum >> 4) & 0xf);
> +        footer[2] = tohex((csum) & 0xf);
> +        g_byte_array_append(gdbserver_state.last_packet, footer, 3);
>   
> -        gdbserver_state.last_packet_len = p - ps;
> -        put_buffer(ps, gdbserver_state.last_packet_len);
> +        put_buffer(gdbserver_state.last_packet->data,
> +                   gdbserver_state.last_packet->len);
>   
>   #ifdef CONFIG_USER_ONLY
>           i = get_char();
> @@ -2812,20 +2813,22 @@ static void gdb_read_byte(GDBState *s, uint8_t ch)
>       uint8_t reply;
>   
>   #ifndef CONFIG_USER_ONLY
> -    if (gdbserver_state.last_packet_len) {
> +    if (gdbserver_state.last_packet->len) {
>           /* Waiting for a response to the last packet.  If we see the start
>              of a new command then abandon the previous response.  */
>           if (ch == '-') {
>               trace_gdbstub_err_got_nack();
> -            put_buffer((uint8_t *)gdbserver_state.last_packet, gdbserver_state.last_packet_len);
> +            put_buffer(gdbserver_state.last_packet->data,
> +                       gdbserver_state.last_packet->len);
>           } else if (ch == '+') {
>               trace_gdbstub_io_got_ack();
>           } else {
>               trace_gdbstub_io_got_unexpected(ch);
>           }
>   
> -        if (ch == '+' || ch == '$')
> -            gdbserver_state.last_packet_len = 0;
> +        if (ch == '+' || ch == '$') {
> +            g_byte_array_set_size(gdbserver_state.last_packet, 0);
> +        }
>           if (ch != '$')
>               return;
>       }
> @@ -3209,7 +3212,7 @@ static int gdb_monitor_write(Chardev *chr, const uint8_t *buf, int len)
>       const char *p = (const char *)buf;
>       int max_sz;
>   
> -    max_sz = (sizeof(gdbserver_state.last_packet) - 2) / 2;
> +    max_sz = MAX_PACKET_LENGTH / 2;
>       for (;;) {
>           if (len <= max_sz) {
>               gdb_monitor_output(&gdbserver_state, p, len);
> 

Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>