[lldb-dev] How to redirect stdin/out/err to different pty?
Piotr Rak
piotr.rak at gmail.com
Wed Mar 26 13:52:59 PDT 2014
No, closing before dup2 is not required, it should close fd and it should
be also atomic. I am wondering now if LLDB sets FileActions like it was
expecting that we use posix_spawn.
I can not check it today... but will look at it tomorrow or during weekend.
2014-03-26 21:33 GMT+01:00 Greg Clayton <gclayton at apple.com>:
> Looks like you might need to look at:
>
> ProcessMonitor::Launch(LaunchArgs *args)
>
> It is what does the fork + exec.
>
> It also looks like no matter what is sent to
> ProcessMonitor::Launch(LaunchArgs *args) for stdin, stdout, stderr, Linux
> _always_ launches using a pseudo terminal by doing:
>
> lldb_utility::PseudoTerminal terminal;
> if ((pid = terminal.Fork(err_str, err_len)) == -1)
>
>
> If you look at the "terminal.Fork()" code you will see that it actually
> sets stdin/out/err to the slave slide of the pseudo terminal, so there is
> no telling if the code in ProcessMonitor::Launch():
>
> if (stdin_path != NULL && stdin_path[0])
> if (!DupDescriptor(stdin_path, STDIN_FILENO, O_RDONLY))
> exit(eDupStdinFailed);
>
> if (stdout_path != NULL && stdout_path[0])
> if (!DupDescriptor(stdout_path, STDOUT_FILENO, O_WRONLY |
> O_CREAT))
> exit(eDupStdoutFailed);
>
> if (stderr_path != NULL && stderr_path[0])
> if (!DupDescriptor(stderr_path, STDERR_FILENO, O_WRONLY |
> O_CREAT))
> exit(eDupStderrFailed);
>
>
> Will work? ProcessMonitor::DupDescriptor() does:
>
>
> bool
> ProcessMonitor::DupDescriptor(const char *path, int fd, int flags)
> {
> int target_fd = open(path, flags, 0666);
>
> if (target_fd == -1)
> return false;
>
> return (dup2(target_fd, fd) == -1) ? false : true;
> }
>
> I would assume you would need to call close() on stdin/out/err first?
> Again the PseudoTerminal::Fork() has always already setup stdin/out/err to
> the slave side and the DupDescriptor calls are probably failing.
>
> Greg
>
>
> On Mar 26, 2014, at 12:26 PM, Piotr Rak <piotr.rak at gmail.com> wrote:
>
> > Hi,
> >
> > That got me curious and now I am bit confused how it works, and it
> should be really simple.
> >
> > I've checked Greg's example, it will just exit before main doing nothing.
> > I've no idea why yet, however I attached my perfect tracee:
> >
> > extern "C" void _start()
> > {
> > __asm__ volatile (
> > "again:;"
> > "int $0x03;"
> > "jmp again;"
> > "movl $1,%eax;"
> > "xorl %ebx, %ebx;"
> > "int $0x80;"
> > );
> > }
> > ls -al /proc/`pidof hello`/fd
> >
> > lrwx------ 1 prak prak 64 03-26 19:42 0 -> /dev/pts/19
> > lrwx------ 1 prak prak 64 03-26 19:42 1 -> /dev/pts/19
> > lrwx------ 1 prak prak 64 03-26 19:42 2 -> /dev/pts/19
> > lrwx------ 1 prak prak 64 03-26 19:42 3 -> /dev/ptmx
> > lrwx------ 1 prak prak 64 03-26 19:42 5 -> /dev/pts/19
> >
> > ls -al /proc/`pidof lldb`/fd
> >
> > lrwx------ 1 prak prak 64 03-26 19:43 0 -> /dev/pts/16
> > lrwx------ 1 prak prak 64 03-26 19:43 1 -> /dev/pts/16
> > lrwx------ 1 prak prak 64 03-26 19:43 2 -> /dev/pts/16
> > lrwx------ 1 prak prak 64 03-26 19:43 3 -> /dev/ptmx
> > lrwx------ 1 prak prak 64 03-26 19:43 4 -> /dev/ptmx
> > lr-x------ 1 prak prak 64 03-26 19:43 5 -> pipe:[1301667]
> > l-wx------ 1 prak prak 64 03-26 19:43 6 -> pipe:[1301667]
> > lr-x------ 1 prak prak 64 03-26 19:43 7 -> pipe:[1299830]
> > l-wx------ 1 prak prak 64 03-26 19:43 8 -> pipe:[1299830]
> >
> > So it was spawned as usual using fork() by Linux/ProcessMonitor.cpp
> > And it was given slave pts, lldb however has no '/tmp/out.txt' file
> anywhere.
> >
> > Should this for this case?:
> > a) be passed opened to inferior before exec, or
> > b) lldb should read master pty and write to /tmp/out.txt
> >
> > I would guess that should be a:
> >
> > But probably then:
> >
> > SetSTDIOFileDescriptor(m_monitor->GetTerminalFD());
> >
> > from ProcessPosix::DoLaunch() ProcessPosix.cpp:253 after creating
> process spoils the fun.
> > Also std{in,err,path)_path had to be empty here.
> >
> > Cheers,
> > /Piotr
> >
> >
> > 2014-03-26 19:08 GMT+01:00 Greg Clayton <gclayton at apple.com>:
> > Seems like we are having some problem re-directing to terminals and
> files that exist. I would try debugging through the launch process and see
> who is doing what with file re-direction. It works on MacOSX just fine, so
> this is probably a linux only issue. Linux does fork() + exec() so some
> code in there isn't doing the right things.
> >
> > % lldb
> > (lldb) settings set target.output-path /tmp/out.txt
> > (lldb) file /bin/ls
> > Current executable set to '/bin/ls' (x86_64).
> > (lldb) run /tmp/
> > (lldb) Process 65933 launched: '/bin/ls' (x86_64)
> > Process 65933 exited with status = 0 (0x00000000)
> > (lldb) q
> >
> > % cat /tmp/out.txt
> > launch-B6FwKk
> > launch-OEyacj
> > launchd-142.5fRyOk
> > launchd-175.RBU3HO
> > launchd-193.Asuh1k
> > launchd-2701.dSHLJu
> > launchd-738.U2ACnW
> > out.txt
> >
> > % xcrun lldb
> > (lldb) settings set target.output-path /tmp/out.txt
> > (lldb) file /bin/ls
> > Current executable set to '/bin/ls' (x86_64).
> > (lldb) run /
> > (lldb) Process 65940 launched: '/bin/ls' (x86_64)
> > Process 65940 exited with status = 0 (0x00000000)
> > (lldb) q
> > lldb:/tmp % cat /tmp/out.txt
> > AppleInternal
> > Applications
> > Library
> > Network
> > SWE
> > System
> > Users
> > Volumes
> > bin
> > cores
> > dev
> > etc
> > home
> > mach_kernel
> > net
> >
> >
> > So this works on Darwin and needs to be fixed on Linux.
> >
> > Greg
> >
> > On Mar 25, 2014, at 7:15 AM, Eran Ifrah <eran.ifrah at gmail.com> wrote:
> >
> > > 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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