[lldb-dev] Launching the program through 'gdb-remote' process plugin

Greg Clayton gclayton at apple.com
Thu Aug 22 09:51:20 PDT 2013 

You probably didn't give LLDB a file with "target create". If you look at the "ProcessGDBRemote::DoLaunch (...)" function, it gets the object file from the target's executable module to ensure there is something to launch:


    ObjectFile * object_file = exe_module->GetObjectFile();
    if (object_file)
    {

        ... send 'A' packet

    }


It really doesn't make sense to run a program that has no executable and has no arguments. If you have a simulator that is debugging something already, then you must reply with a non-zero PID to the "qC" packet. Below your packets were:

<   6> send packet: $qC#b4
<   1> read packet: +
<   7> read packet: $QC0#c4
<   1> send packet: +

This is telling us, we are connected, but aren't debugging anything yet. There is a bug in LLDB right now if this is the case where we aren't propagating an error back from Process::Launch() correctly stating the 'A' packet can't be sent without a valid executable.

IS this what is going on? If so, just give lldb the executable file:

(lldb) target create --arch <ARCH> /path/to/local/copy/of/sim/exe/a.out
(lldb) process connect --plugin gdb-remote connect://localhost:51000

On Aug 21, 2013, at 10:14 PM, chansarav <chansarav at gmail.com> wrote:

> Thanks for the reply.
> 
> I enabled the packet logging in LLDB.
> 
> (lldb) log enable gdb-remote packets
> (lldb) process connect --plugin gdb-remote connect://localhost:51000
> <   1> send packet: +
> history[1] tid=0xb1d819d0 <   1> send packet: +
> <  26> send packet: $QThreadSuffixSupported#e4
> <   1> read packet: +
> <   4> read packet: $#00
> <   1> send packet: +
> <  27> send packet: $QListThreadsInStopReply#21
> <   1> read packet: +
> <   7> read packet: $E01#a6
> <   1> send packet: +
> <  10> send packet: $vCont?#49
> <   1> read packet: +
> <  15> read packet: $vCont[;c;s]#0e
> <   1> send packet: +
> <  27> send packet: $qVAttachOrWaitSupported#38
> <   1> read packet: +
> 
> <   6> send packet: $qC#b4
> <   1> read packet: +
> <   7> read packet: $QC0#c4
> <   1> send packet: +
> (lldb) run
> 
> After this lldb just hangs. lldb doesn't send any packet after the 'run' command. I debugged by inserting a breakpoint in lldb's code which sends the 'A' packet. And that breakpoint was not hit.
> 
> 
> 
> On Wed, Aug 21, 2013 at 10:31 PM, Greg Clayton <gclayton at apple.com> wrote:
> The "process launch" command should send the 'A' packet, and it is waiting for a stop reply response from the 'A' packet. Try enabling the packet logging in LLDB:
> 
> (lldb) log enable gdb-remote packets
> (lldb) process connect ...
> (lldb) run
> 
> My guess is that the 'A' packet isn't responding with a stop reply packet.
> 
> On Aug 21, 2013, at 7:47 AM, chansarav <chansarav at gmail.com> wrote:
> 
> > Hi,
> >
> > I am connecting lldb with my simulator through 'gdb-remote' process plugin. After extablishing the connection, I want to issue the 'process launch' command in lldb which should send the arguments packet 'A' to simulator asking it to launch the program.
> >
> > I am facing the problem while issuing the 'process launch' command in lldb. When I give the 'process launch' command, lldb hangs and there is no communication with simulator. When I debugged with gdb, I got the backtrace as follows:
> >
> > #2  0xb6703a6f in lldb_private::Condition::Wait (this=0x8077dac, mutex=..., abstime=0x0, timed_out=0xbfffaa9f) at /home/chandra/llvm-3.1/tools/lldb/source/Host/common/Condition.cpp:92
> > #3  0xb662768d in lldb_private::Predicate<bool>::WaitForValueEqualTo (this=0x8077d90, value=true, abstime=0x0, timed_out=0xbfffaa9f) at /home/chandra/llvm-3.1/tools/lldb/source/Core/../../include/lldb/Host/Predicate.h:317
> > #4  0xb662b03f in lldb_private::Listener::WaitForEventsInternal (this=0x8077d3c, timeout=0x0, broadcaster=0xadb0179c, broadcaster_names=0x0, num_broadcaster_names=0, event_type_mask=3, event_sp=...) at /home/chandra/llvm-3.1/tools/lldb/source/Core/Listener.cpp:409
> > #5  0xb662b1f7 in lldb_private::Listener::WaitForEventForBroadcasterWithType (this=0x8077d3c, timeout=0x0, broadcaster=0xadb0179c, event_type_mask=3, event_sp=...) at /home/chandra/llvm-3.1/tools/lldb/source/Core/Listener.cpp:440
> > #6  0xb69421ec in lldb_private::Process::WaitForStateChangedEvents (this=0xadb01788, timeout=0x0, event_sp=...) at /home/chandra/llvm-3.1/tools/lldb/source/Target/Process.cpp:1069
> > #7  0xb6941f2c in lldb_private::Process::WaitForProcessToStop (this=0xadb01788, timeout=0x0) at /home/chandra/llvm-3.1/tools/lldb/source/Target/Process.cpp:977
> > #8  0xb6587d98 in CommandObjectProcessLaunch::DoExecute (this=0x80813d0, launch_args=..., result=...) at /home/chandra/llvm-3.1/tools/lldb/source/Commands/CommandObjectProcess.cpp:220
> > #9  0xb672c999 in lldb_private::CommandObjectParsed::Execute (this=0x80813d0, args_string=0xb4d667bc "", result=...) at /home/chandra/llvm-3.1/tools/lldb/source/Interpreter/CommandObject.cpp:856
> > #10 0xb67215d3 in lldb_private::CommandInterpreter::HandleCommand (this=0x8077fc8, command_line=0x883a614 "process launch", lazy_add_to_history=lldb_private::eLazyBoolYes, result=...,
> >     override_context=0x0, repeat_on_empty_command=true, no_context_switching=false) at /home/chandra/llvm-3.1/tools/lldb/source/Interpreter/CommandInterpreter.cpp:1571
> > #11 0xb64e0ced in lldb::SBCommandInterpreter::HandleCommand (this=0xbfffc2cc, command_line=0x883a614 "process launch", result=..., add_to_history=true) at /home/chandra/llvm-3.1/tools/lldb/source/API/SBCommandInterpreter.cpp:97
> > #12 0x0805a103 in Driver::HandleIOEvent (this=0xbfffec7c, event=...) at /home/chandra/llvm-3.1/tools/lldb/tools/driver/Driver.cpp:996
> > #13 0x0805b516 in Driver::MainLoop (this=0xbfffec7c) at /home/chandra/llvm-3.1/tools/lldb/tools/driver/Driver.cpp:1430
> > #14 0x0805bbf2 in main (argc=4, argv=0xbfffede4, envp=0xbfffedf8) at /home/chandra/llvm-3.1/tools/lldb/tools/driver/Driver.cpp:1562
> >
> > Though I am analyzing on this, Can someone help me in finding out what goes wrong while trying to launch a program in simulator through 'gdb-remote' process plugin?
> >
> >
> > Following is the communication between lldb and simulator for the "process connect --plugin gdb-remote connect://localhost:51000" command.
> >
> > Send Packet: QStartNoAckMode: 15 chars
> > Read Packet:
> > Send Packet: QThreadSuffixSupported: 22 chars
> > Read Packet:
> > Send Packet: QListThreadsInStopReply: 23 chars
> > Read Packet: E01
> > Send Packet: qHostInfo: 9 chars
> > Read Packet: cputype:201;cpusubtype:-2;ostype:unknown;vendor:unknown;endian:little;ptrsize:4;
> > Send Packet: vCont?: 6 chars
> > Read Packet: vCont[;c;s]
> > Send Packet: qVAttachOrWaitSupported: 23 chars
> > Read Packet:
> > Send Packet: qC: 2 chars
> > Read Packet: QC0
> >
> > LLDB sets the status as connected after this communication.
> > (snip start)
> >     if (pid == LLDB_INVALID_PROCESS_ID)
> >     {
> >         // We don't have a valid process ID, so note that we are connected
> >         // and could now request to launch or attach, or get remote process
> >         // listings...
> >         SetPrivateState (eStateConnected);
> >     }
> > (snip end)
> > function: ProcessGDBRemote::DoConnectRemote ()
> >
> > Thanks,
> > Chandra Kumar R.
> > _______________________________________________
> > lldb-dev mailing list
> > lldb-dev at cs.uiuc.edu
> > http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
> 
>

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