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Date:	Mon, 3 May 2021 01:16:25 +0900
To:	cygwin AT cygwin DOT com
Subject:	Re: GDB looses pgrp setting in the terminal for debugged process
	after break.
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From:	Takashi Yano via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>
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On Sat, 6 Feb 2021 00:26:54 +0900
Takashi Yano wrote:
> On Fri, 5 Feb 2021 19:34:57 +0900
> Takashi Yano wrote:
> > 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?
> 
> The patch below seems to be better than the previous one a bit.
> 
> diff --git a/inflow.c.orig b/inflow.c
> index 00b2235..fa7b408 100644
> --- a/inflow.c.orig
> +++ b/inflow.c
> @@ -40,6 +40,10 @@
>  #include <sys/ioctl.h>
>  #endif
>  
> +#ifdef __CYGWIN__
> +#include <sys/cygwin.h>
> +#endif
> +
>  #ifndef O_NOCTTY
>  #define O_NOCTTY 0
>  #endif
> @@ -367,7 +371,13 @@ child_terminal_inferior (struct target_ops *self)
>  	     time the inferior was running.  See also comments
>  	     describing terminal_state::process_group.  */
>  #ifdef HAVE_GETPGID
> +#ifdef __CYGWIN__
> +	  pid_t cygpid = cygwin_internal (CW_WINPID_TO_CYGWIN_PID, inf->pid);
> +	  if (cygpid <= cygwin_internal (CW_MAX_CYGWIN_PID))
> +	    result = tcsetpgrp (0, getpgid (cygpid));
> +#else
>  	  result = tcsetpgrp (0, getpgid (inf->pid));
> +#endif
>  #else
>  	  result = tcsetpgrp (0, tinfo->process_group);
>  #endif

I confirmed that gdb-10.2-1 (TEST) still has this problem.

-- 
Takashi Yano <takashi DOT yano AT nifty DOT ne DOT jp>

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