Re: GDB looses pgrp setting in the terminal for debugged process after break.

[Takashi Yano <takashi.yano@nifty.ne.jp>]

On Tue, 26 Jan 2021 12:14:02 +0900
Takashi Yano wrote:
> Hi GDB maintainer,
> 
> In GDB, debugged process cannot continue execution after break
> if it reads stdin.
> 
> With the following steps, cat is terminated with error.
> 
> 1) Install coreutils-debuginfo package.
> 2) Run "gdb cat" in console (command prompt), not in mintty.
> 3) Enter "start" in gdb.
> 4) Enter "cont" in gdb.
> 
> This results in:
> /usr/bin/cat: -: Input/output error
> 
> Both gdb-9.2-1 and gdb-10.1-1(TEST) have this problem.
> 
> I looked into this problem and found the cause is that the pgid
> setting for /usr/bin/cat is lost after break. The following patch
> for GDB source resolves the issue. In the following section,
> winpid is passed to getpgid() rather than cygwin pid. Also, winpid
> is passed to other POSIX system calls such as kill() elsewhere. 
> 
> --- inflow.c.orig	2020-05-24 06:10:29.000000000 +0900
> +++ inflow.c	2021-01-23 17:48:27.963609500 +0900
> @@ -364,11 +364,11 @@
>  #ifdef HAVE_TERMIOS_H
>  	  /* If we can't tell the inferior's actual process group,
>  	     then restore whatever was the foreground pgrp the last
>  	     time the inferior was running.  See also comments
>  	     describing terminal_state::process_group.  */
> -#ifdef HAVE_GETPGID
> +#if defined (HAVE_GETPGID) && !defined (__CYGWIN__)
>  	  result = tcsetpgrp (0, getpgid (inf->pid));
>  #else
>  	  result = tcsetpgrp (0, tinfo->process_group);
>  #endif
>  	  if (result == -1)
> 
> 
> I hope the GDB maintainer will check it out.
> 
> Addresses: https://cygwin.com/pipermail/cygwin-patches/2021q1/011018.html

I have noticed that cygwin gdb essentially has the problem
regarding terminal process group.

Cygwin gdb uses CreateProcessW() to execute debugging process
rather than exec(). If the debugging process is a cygwin process,
cygwin pid is assigned, however, if the debugging process is a
non cygwin process, cygwin pid is not assigned. Therefore, there
is no appropriate process group ID to set.

I wonder what is the right thing under that situation. Any idea?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>