[lldb-dev] How to redirect stdin/out/err to different pty?
Greg Clayton
gclayton at apple.com
Wed Mar 26 13:33:17 PDT 2014
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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