Re: [PATCH v2 16/16] Document pseudo-terminal and interrupting changes

[Pedro Alves <pedro@palves.net>]

Hi!

On 2021-06-15 1:56 p.m., Eli Zaretskii wrote:
>> +On such systems, in some cases, like for example if you need to run
>> +your program and then detach it, and you want the program to remain
>> +associated with a terminal, you may prefer that @value{GDBN} starts
>> +your program using the same device for standard input and output as
>> +@value{GDBN} is using.
> IMHO, this is a misfeature.  If the terminal from which GDB was run
> remains on the system, it would be an unpleasant surprise for the user
> that the program gets hit by SIGHUP when you detach.  I think we
> should try to avoid this side effect, if that's feasible.
> 

Hmm, I'm not sure I follow what you're saying here, maybe I'm misunderstanding.

We no longer get a SIGHUP on detach, that was fixed on v2.  What the text is saying now is
different: because when you start your program with "run", the terminal the inferior is
associated with was created by GDB, when you "detach", GDB destroys the terminal.  The
result is that the program you detached from loses its terminal.  From the detached
program's perspective, it's the same as with current GDB when you do "run", then "detach",
and then close the GDB terminal.  The difference is that with my patches the program
loses its terminal a step earlier.  In v1, the detached program would also get a SIGHUP, 
but that was fixed in v2, it no longer does.

If you really need to do "run" and then "detach" for some reason, _and_ you want
your program to have a terminal, you should start the program with a specified
terminal, like:

 - start the program outside gdb, and then use "attach".  Make sure the terminal
   you started the program at remains alive.

 - use the "tty" command to tell GDB to start the program on some specified terminal 
   (which will outlive gdb and gdb's terminal)

If you're sure gdb's terminal will stay around, and you want to tell GDB to start
the program on that terminal, you can use the "tty /dev/tty" command before starting
the program.

Is this clearer?  I can try to adjust the documentation to explain this better and be more
descriptive like above. 

Thanks,
Pedro Alves