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

["Maciej W. Rozycki" <macro@orcam.me.uk>]

On Thu, 12 Mar 2026, 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)
>    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);
> +
> +  if (tcsetattr (fd, TCSANOW, &tio) < 0)
> +    perror_with_name (_("Cannot set custom baud rate"));

 It doesn't appear to me this code should be wrapped in:

#if ... && defined(BOTHER)

or for that matter be a part of `set_custom_baudrate_linux' (which AFAICT 
should be left alone, or please point me at what actually you have changed 
there that is not pure code massaging) as this is now platform-agnostic 
(and I believe GNU Hurd has always supported arbitrary baud rates using 
this interface).  I'm leaving it up to you to come up with a name for this 
new variant of the function.

 Also ISTM that HAVE_CUSTOM_BAUDRATE_SUPPORT now also needs to be set if 
HAVE_CFSETSPEED_ARBITRARY rather than relying on BOTHER to be defined as 
well, which may not necessarily be the case (cf. GNU Hurd again).

> +#else
> +  error (_("Custom baud rate not supported on this platform"));
> +#endif

 This shouldn't be needed as this code is not supposed to be ever compiled 
if !HAVE_CUSTOM_BAUDRATE_SUPPORT (IOW don't set the macro instead if the 
conditions required are not met).

  Maciej