Re: [PATCH V3] PR gdb/33747: gdb/ser-unix: modernize Linux custom baud rate support

[Kevin Buettner <kevinb@redhat.com>]

On Thu, 12 Mar 2026 14:01:06 -0700
sunilkumar.dora@windriver.com wrote:

> diff --git a/gdb/ser-unix.c b/gdb/ser-unix.c
> index c295a9c5ba1..a15f4cc2162 100644
> --- a/gdb/ser-unix.c
> +++ b/gdb/ser-unix.c
> @@ -510,36 +510,59 @@ set_baudcode_baudrate (struct serial *scb, int
> baud_code) 
>  #if HAVE_CUSTOM_BAUDRATE_SUPPORT && defined(BOTHER)
>  
> -/* Set a custom baud rate using the termios BOTHER.  */
> +/* Set a custom baud rate.
> +
> +   Prefer the POSIX cfsetispeed/cfsetospeed interface when it accepts
> +   arbitrary baud rates.  Otherwise fall back to Linux-specific termios2
> +   (BOTHER) or legacy termios interfaces.  */
>  
>  static void
>  set_custom_baudrate_linux (int fd, int rate)
>  {
> -#ifdef TCGETS2
> -  struct termios2 tio;
> -  const unsigned long req_get = TCGETS2;
> -  const unsigned long req_set = TCSETS2;
> -#else
> +#if defined(HAVE_CFSETSPEED_ARBITRARY)

Can you add a comment about how this code path is supported by glibc
2.42+ ?  You could also mention that this behavior is expected to be
standardized by a future POSIX revision.

>    struct termios tio;
> -  const unsigned long req_get = TCGETS;
> -  const unsigned long req_set = TCSETS;
> -#endif
> +  if (tcgetattr (fd, &tio) < 0)
> +    perror_with_name (_("Cannot get current baud rate"));
> +
> +  cfsetispeed (&tio, rate);
> +  cfsetospeed (&tio, rate);

Return values for cfsetispeed and cfsetospeed should be checked.  If
either call fails, it should either error out or try another way of
setting the speed.

Kevin