GNU bug report logs -
#49524
28.0.50; make-serial-process is not portable
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Reported by: Ken Brown <kbrown <at> cornell.edu>
Date: Sun, 11 Jul 2021 15:31:01 UTC
Severity: normal
Found in version 28.0.50
Done: Ken Brown <kbrown <at> cornell.edu>
Bug is archived. No further changes may be made.
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On 7/12/2021 9:27 AM, Ken Brown wrote:
> On 7/11/2021 12:24 PM, Eli Zaretskii wrote:
>>> From: Ken Brown <kbrown <at> cornell.edu>
>>> Date: Sun, 11 Jul 2021 11:24:58 -0400
>>>
>>> Fmake_serial_process calls Fserial_process_configure, which calls
>>> serial_configure, which calls cfsetspeed with the speed argument equal to the
>>> numerical baud rate (e.g., 9600). But the documentation of cfsetspeed says that
>>> the speed argument must be one of the Bnnn constants defined in termios.h (e.g.,
>>> B9600). See, for example,
>>>
>>> https://man7.org/linux/man-pages/man3/termios.3.html
>>>
>>> This incorrect call of cfsetspeed happens to succeed on GNU/Linux because
>>> glibc's cfsetspeed allows the argument to be the numerical baud rate, which it
>>> converts to the appropriate Bnnn constant. But I don't think emacs should be
>>> relying on this undocumented behavior. In particular, this doesn't work on
>>> Cygwin. And it wouldn't even work on GNU/Linux if emacs used the cfsetspeed
>>> replacement defined in sysdep.c instead of glibc's cfsetspeed.
>>>
>>> I think the way to fix this is to imitate the glibc code that converts the baud
>>> rate to a Bnnn constant, but maybe someone has a better idea.
>>
>> Converting in sysdep.c:serial_configure sounds TRT to me.
>
> Patch attached.
BTW, we've decided to change Cygwin's cfsetspeed to be compatible with glibc's,
so the problem fixed by my patch won't exist on Cygwin going forward. And I
checked FreeBSD out of curiosity and found that there's no issue there either
because of the way they define the Bnnn constants:
#define B0 0
#define B50 50
#define B75 75
...
So I should probably remove the reference to non-glibc platforms in my commit
message.
Ken
This bug report was last modified 3 years and 315 days ago.
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