[lldb-dev] How to redirect stdin/out/err to different pty?

Tue Mar 25 07:15:24 PDT 2014

Hello Greg,
Thanks for the input. It still does not work ( I rewrote my terminal code
to look similar to lldb's PseudoTerminal, and it is still not working)

To simplify things, I tried some basic things with the *command line* tool
'lldb':

I created a file ~/.lldbinit with the following content:

eran at eran-linux: ~/llvm/build/bin $ cat ~/.lldbinit
settings set target.output-path /tmp/dbg.out
eran at eran-linux: ~/llvm/build/bin $

I then ran lldb while having tail -f /tmp/dbg.out& in another terminal to
see if the stdout is being redirected

Now, this is the interesting part:
In the first run when the file /tmp/dbg.out was empty - the redirection
worked (tail showed the debuggee stdout)
In the second run (and later) - nothing was written to the file

However, if I truncate the file using the below command:

$ > /tmp/dbg.out

and run lldb again - I see the stdout again - but same as before only for
the first time (i.e. as long as the file is empty the stdout was redirected)

The next thing I tried was to use a terminal name for redirection:

- Open a new terminal and type `tty` (in my case it gave /dev/pts/19 )
- Edit the ~/.lldbinit: settings set target.output-path /dev/pts/19
- Start lldb and verify that the setting is set properly by running: settings
show target.output-path
- Run the program under lldb - the output is not redirected (i.e. it is
show in the same console where I ran lldb)

Any ideas?

P.S.
Sorry if this looks like a voodoo, but this is what I am getting here... ;)

Eran

On Mon, Mar 24, 2014 at 6:46 PM, Greg Clayton <gclayton at apple.com> wrote:

> Check out the PseudoTerminal class in
> trunk/source/Utility/PseudoTerminal.cpp.
>
> See the function named PseudoTerminal::OpenFirstAvailableMaster(...). You
> must call posix_openpt, grantpt, and unlockpt. I am guessing that because
> you aren't calling grantpt and granting access to the slave you are failing
> to be able to use the slave in your child process.
>
> Greg Clayton
>
> On Mar 23, 2014, at 11:32 AM, Eran Ifrah <eran.ifrah at gmail.com> wrote:
>
> > Sure, thanks for the help so far
> > Eran
> >
> >
> > On Sun, Mar 23, 2014 at 8:31 PM, Piotr Rak <piotr.rak at gmail.com> wrote:
> > I am sorry, but nothing obvious comes to me right now, probably you'll
> need to wait for Monday, when people more familiar with lldb will be able
> to help you debug this problem.
> >
> >
> > 2014-03-23 16:07 GMT+01:00 Eran Ifrah <eran.ifrah at gmail.com>:
> >
> >
> >
> >
> > On Sun, Mar 23, 2014 at 4:29 PM, Piotr Rak <piotr.rak at gmail.com> wrote:
> > Sorry I misinformed you about posix_spawn - it is not true for Linux and
> FreeBSD at least, it will use ordinary fork.
> >
> >
> > 2014-03-23 15:23 GMT+01:00 Piotr Rak <piotr.rak at gmail.com>:
> >
> >
> > Hi,
> >
> > 2014-03-23 14:04 GMT+01:00 Eran Ifrah <eran.ifrah at gmail.com>:
> >
> > Thanks for your pointer Piotr. Here is the code I am using to open a
> pseudo-terminal (there is the UI part, which I left out):
> >
> >     char __name[128];
> >     memset(__name, 0, sizeof(__name));
> >
> >     int master(-1);
> >     m_slave = -1;
> >     if(openpty(&master, &m_slave, __name, NULL, NULL) != 0)
> >         return wxT("");
> >
> >     // disable ECHO
> >     struct termios termio;
> >     tcgetattr(master, &termio);
> >     termio.c_lflag = ICANON;
> >     termio.c_oflag = ONOCR | ONLRET;
> >     tcsetattr(master, TCSANOW, &termio);
> >
> >     m_tty = wxString(__name, wxConvUTF8);
> >
> > At the end, m_tty contains a string name (e.g. /dev/pts/19 ).
> > Note that the above code works flawlessly when using it with gdb (i.e.
> if I pass this "/dev/pts/19" to gdb's switch -tty=/dev/pts/19 I will get
> all the inferior output/err/input to my internal terminal)
> >
> > However, doing the same with LLDB (using C++ API not the command line ,
> i.e. passing "/dev/pts/19" as an argument to SBTarget::Launch(...)) I get
> nothing as output...
> >
> > Looks sane to me.
> >
> > Also, I am not sure I am following the idea behind replacing the
> "Launch" function with my own fork(), looking at the code of Launch()
> suggests that it does more than a simple fork...
> >
> >
> > That was my idea to debug issue if nothing else helps.
> > Or rather bisect on which side it really is, sorry if I did not make it
> clear...
> > So I was trying suggest replacing SBTarget::Launch with fork,  write to
> child stdout/err, and see if that works alone....
> >
> > SBTarget::Launch is usually actually posix_spawn right now, it uses
> posix_spawnattr_addopen to open descriptors for your specified paths, and
> should open it 3 times - given current implementation - even it is just one
> file.
> >
> > Have you inspected SBProcess and SBError returned by SBTarget::Launch?
> >
> > I checked IsValid() on both and its OK for both. I can actually run
> "next" Continue etc and seems to be working. Its just that I can't seem to
> redirect the stdout/err to my own console.
> >
> >
> > Do you see your inferior process is indeed launching, just not
> displaying anything?
> > Yes, ps -ef shows the debugee
> >
> > Do you have an option to check if those terminals are actually being
> opened (like examining /proc/<pid>/fd for linux)?
> > The terminal is opened. Like I mentioned in my previous email, using the
> _same_ code with gdb works
> > I also have a standalone terminal application which I wrote which is
> also using the same set of classes all of the are working for couple of
> years now without any problems
> >
> > I also tried this:
> > I typed in my konsole 'tty' and used that as the input for Launch - it
> also seems to have no effect
> >
> >
> >
> > Good luck,
> > /Piotr
> >
> > Any more hints?
> > Eran
> >
> >
> >
> > On Sat, Mar 22, 2014 at 9:36 PM, Piotr Rak <piotr.rak at gmail.com> wrote:
> > Hi,
> >
> > It should.
> > Have you opened master pseudoterminal like?:
> >
> > int fd = posix_openpt(flags); // open("/dev/ptmx") might work here too
> but less portable;
> > grantpt(fd);
> > unlockpt(fd);
> >
> > Depending on target you might need some bizarre ioctls here, but
> assuming you are using Linux/FreeBSD/MacOSX
> > you should be fine.
> >
> > If you had already master pseudo-terminal file descriptor you can skip
> steps above.
> >
> > You can use ptsname for master file descriptor it will return you name
> of slave pseudo-terminal for your master.
> > Later you can pass name returned by ptsname(fd) as Launch arguments.
> >
> > If above won't work you can try replacing Launch() call with ordinary
> fork, and in child process:
> >
> > slavefd = open(slavename, O_RDWR);
> >
> > dup2(0, slavefd);
> > dup2(1, slavefd);
> > dup2(2, slavefd);
> >
> > And see if that works alone for you...
> >
> > Good luck,
> > /Piotr
> >
> >
> > 2014-03-22 19:29 GMT+01:00 Eran Ifrah <eran.ifrah at gmail.com>:
> > Hello,
> >
> > I am trying to use the C++ API with good success so far.
> > I am now at a point where I want to redirect stdin/out/err of the
> inferior to my application (my application creates a separate pseudo
> terminal window)
> >
> > Looking at the SBTarget::Launch, I thought that simply passing
> "/dev/pts/<some-number>" as the 3rd, 4th and 5th argument will do the trick
> .. well, it did not.
> > I am missing something basic here, can anyone shed some light please? or
> give an example (better) of how to achieve this?
> >
> > Thanks!
> >
> > --
> > Eran Ifrah
> > Author of codelite, a cross platform open source C/C++ IDE:
> http://www.codelite.org
> > wxCrafter, a wxWidgets RAD: http://wxcrafter.codelite.org
> >
> > _______________________________________________
> > lldb-dev mailing list
> > lldb-dev at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
> >
> >
> >
> >
> >
> > --
> > Eran Ifrah
> > Author of codelite, a cross platform open source C/C++ IDE:
> http://www.codelite.org
> > wxCrafter, a wxWidgets RAD: http://wxcrafter.codelite.org
> >
> >
> >
> >
> >
> > --
> > Eran Ifrah
> > Author of codelite, a cross platform open source C/C++ IDE:
> http://www.codelite.org
> > wxCrafter, a wxWidgets RAD: http://wxcrafter.codelite.org
> >
> >
> >
> >
> > --
> > Eran Ifrah
> > Author of codelite, a cross platform open source C/C++ IDE:
> http://www.codelite.org
> > wxCrafter, a wxWidgets RAD: http://wxcrafter.codelite.org
> > _______________________________________________
> > lldb-dev mailing list
> > lldb-dev at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>
>

-- 
Eran Ifrah
Author of codelite, a cross platform open source C/C++ IDE:
http://www.codelite.org
wxCrafter, a wxWidgets RAD: http://wxcrafter.codelite.org
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