[SeaBIOS] Re: [PATCH] sercon: add missing GET_LOW() to access rx_bytes

[Volker Rümelin]

> On Wed, Jan 19, 2022 at 10:08:49PM +0100, Volker Rümelin wrote:
> > The variable rx_bytes is marked VARLOW. Add a missing GET_LOW()
> > to access rx_bytes.
> >
> > Reported-by: Gabe Black 
> > Signed-off-by: Volker Rümelin
>
> Thanks.  Good catch!
>
> I think we should fix this by copying the contents into a local
> variable to hopefully avoid this type of error in the future.  Patch
> below.
>
> -Kevin

The patch looks good. Are you going to send the patch to the mailing 
list or should I do it?

With best regards,
Volker
> --- a/src/sercon.c
> +++ b/src/sercon.c
> @@ -626,7 +626,7 @@ sercon_check_event(void)
>       u16 addr = GET_LOW(sercon_port);
>       u16 keycode;
>       u8 byte, count = 0;
> int seq, chr;
>
> int seq;
>
> // check to see if there is a active serial port
>  if (!addr)
>
> @@ -640,20 +640,23 @@ sercon_check_event(void)
>       // read all available data
>       while (inb(addr + SEROFF_LSR) & 0x01) {
>           byte = inb(addr + SEROFF_DATA);
>    if (GET_LOW(rx_bytes) < sizeof(rx_buf)) {
>        SET_LOW(rx_buf[rx_bytes], byte);
>        SET_LOW(rx_bytes, GET_LOW(rx_bytes) + 1);
>    u8 rb = GET_LOW(rx_bytes);
>    if (rb < sizeof(rx_buf)) {
>        SET_LOW(rx_buf[rb], byte);
>        SET_LOW(rx_bytes, rb + 1);
>         count++;
>     }
> }
>
> for (;;) {
>     // no (more) input data
>    if (!GET_LOW(rx_bytes))
>    u8 rb = GET_LOW(rx_bytes);
>    if (!rb)
>         return;
>
>     // lookup escape sequences
>    if (GET_LOW(rx_bytes) > 1 && GET_LOW(rx_buf[0]) == 0x1b) {
>    u8 next_char = GET_LOW(rx_buf[0]);
>    if (rb > 1 && next_char == 0x1b) {
>         seq = findseq();
>         if (seq >= 0) {
>             enqueue_key(GET_GLOBAL(termseq[seq].keycode));
>
> @@ -664,12 +667,11 @@ sercon_check_event(void)
>       // Seems we got a escape sequence we didn't recognise.
>       //  -> If we received data wait for more, maybe it is just incomplete.
>    if (GET_LOW(rx_buf[0]) == 0x1b && count)
>    if (next_char == 0x1b && count)
>         return;
>
>     // Handle input as individual char.
>    chr = GET_LOW(rx_buf[0]);
>    keycode = ascii_to_keycode(chr);
>    keycode = ascii_to_keycode(next_char);
>     if (keycode)
>         enqueue_key(keycode);
>     shiftbuf(1);