Re: [PATCH] gdb/ser-unix: avoid musl build failure when setting custom baud rates

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

On Fri, 13 Feb 2026, Kevin Buettner wrote:

> 2) I don't think that it's correct to call cfsetospeed and cfsetispeed
>    with arbitrary baud rates.  According to the man page, these
>    functions expect to be passed one of the "B" constants like B1200,
>    B9600, etc, not arbitrary speeds.  The existing code which uses the
>    BOTHER extension is the correct way to do this.

 FYI as from v2.42 glibc finally does support arbitrary baud rates with 
`cfsetospeed' and `cfsetispeed' with Linux as well, in addition to Hurd, 
which it has been since forever.  This is fully documented in the glibc 
manual; the man page you refer to is likely outdated.

 The BOTHER flag is the raw OS kernel interface and its direct use is 
discouraged.

 Cf. 
<https://inbox.sourceware.org/libc-alpha/20250612013546.1524096-1-hpa@zytor.com/>, 
<https://sourceware.org/bugzilla/show_bug.cgi?id=10339>, 
<https://sourceware.org/git/gitweb.cgi?p=glibc.git;h=5f138519ebdf88e1fc5395d65df0b780dd07829a>.  
The position of the POSIX committee WRT the API is quoted there.

 You can use autoconf to determine whether arbitrary baud rates are 
supported, by checking if one of the Bxxx macros expands to its numeric 
baud rate equivalent (you can check a couple if you feel pedantic).  

 With older versions of glibc and possibly other C library 
implementations Bxxx macros have to be used of course and the choice of 
baud rates available this way is limited.  Resorting to using the BOTHER 
flag might be the best approach, but the POSIX interface seems like the 
best first choice.

  Maciej