[lldb-dev] Remote debugging with lldb

Filipe Cabecinhas filcab+lldb-dev at gmail.com
Thu Aug 25 17:52:49 PDT 2011


Thanks for your reply. It's nice to know that I was on the right path :-)

But I still have some questions:

On Thu, Aug 25, 2011 at 15:32, Greg Clayton <gclayton at apple.com> wrote:

> On Aug 24, 2011, at 6:11 PM, Filipe Cabecinhas wrote:
> > Hi,
> >
> > I'm trying to do remote debugging with lldb, but I keep running into
> problems.
> >
> > How should I do it?
> >
> > I tried running "debugserver localhost:42000" and then, on the lldb
> client:
> >
> > platform select (remote-macosx | remote-gdb-server?) + platform connect?
> > platform select … + process connect?
> The platform stuff is still a work in progress which we hope to really
> perfect over the next year. If you are doing Mac to Mac debugging the best
> thing to do right now is:
> AFP mount the root drive on the other machine. For these examples lets
> suppose we have machine1 and machine2. So the flow would be:
> - machine1: start debugserver:
> machine1 % debugserver localhost:12345 /bin/ls
> - machine2: mount the root drive from machine2 and launch lldb:
> machine2 % ./lldb
> (lldb) platform select remote-macosx --sysroot /Volumes/machine1
> (lldb) process connect connect://machine1:12345
> This should do it. Currently the platforms don't do any file copying from
> one to the other, so you will need a copy of all executables and shared
> libraries to exist within the "Volumes/machine1" directory. So if you are
> running "/bin/ls" it should be available through your mount at:
> "/Volumes/machine1/bin/ls". Likewise for all shared libraries.
Is the remote-macosx platform the one to choose in order to have more
information about the program? Or could I also choose the remote-gdb-server
platform (which seems more generic)? Is there some code that "isn't there
yet" on the remote-gdb-server?

I managed to run the program with both, but where is the difference between
them? Or is it the same because you've wired the macosx-host platform to
just start a remote-gdb-server?

> >
> > I would suppose you need the plugins for the combinations you want to
> use, but with the gdb-remote stuff, I'm getting confused.
> >
> > In lldb_private::Initialize(), we initialize several plugins, depending
> on the operating system. I'm supposing the DynamicLoader and Process plugins
> (along with some others) are only needed when running as host, otherwise, we
> couldn't, on Linux, debug a FreeBSD or Mac OS X target (since their
> initialization gets ifdeffed out).
> >
> None of these should really be ifdefed out, they should be being compiled
> on all platforms, excluding any "native only" plug-ins.

So, in the future, lldb.cpp will simply run all that code, except for some
of the Platform (and Process?) plugins? I'm supposing it's most of them,
since many depend on the debuggee, and not the platform where lldb is
running (just the remote server).

> I saw that, on Mac OS X, lldb spawns a debugserver that runs the program
> and they communicate using the plugin ProcessGDBRemote (another question:
> Why is that plug-in only started on Mac OS X? It has to run on the host, but
> otherwise I didn't see much platform-specific stuff (I just skimmed the
> file)). Shouldn't that Process plugin be also used with a
> PlatformRemoteGDBServer?
> >
> The platform (currently on MacOSX built as the "lldb-platform" executable)
> can currently do the job of being launched on a remote host and it can spawn
> a new debugserver in order to debug a process on the host, list processes,
> attach to existing process and do much more. All the code that the
> "lldb-platform" uses if from the "lldb_private::Host" API layer, so it
> completely reuses the host code that  can launch processes for debugging,
> and much more.
> The ideal platform looking forward would:
> - be a binary that runs natively on the remote machine that hopefully can
> be automatically launched when the remote host is contacted on a port. On
> MacOSX, we can add a launchd plist entry that would automatically launch
> "lldb-platform" (or any equivalent) when the remote host is contacted on a
> fixed port number.
> - upload and download files from the platform and cache them locally
> (currently we require all files to be there already in the "--sysroot" for
> the platform)
> - list and query info for existing processes (lldb-platform can already do
> this)
> - launch a process whose executable exists on the remote host (possibly
> just updloaded via the platform) with any args required. This would spawn
> the process under a debugserver and return the port needed to connect.
> - attach to an existing process (spawn a debugserver that will attach, an
> return the port number across the platform protocol)
> So much of this works right now. You can try out the "lldb-platform" binary
> with the current build and pretend to debug remotely:
> % ./lldb-platform --listen 1444
> Listening for a connection on 1444...
> Then launch lldb and connect:
> % ./lldb
> (lldb) platform select remote-macosx
>  Platform: remote-macosx
>  Connected: no
> (lldb) platform connect connect://localhost:1444
>  Platform: remote-macosx
>    Triple: x86_64-apple-darwin
> OS Version: 10.7.1
>    Kernel: Darwin Kernel Version 11.2.0: Tue Aug  9 20:54:00 PDT 2011;
> root:xnu-1699.24.8~1/RELEASE_X86_64
>  Hostname: myhost.apple.com
>  Connected: yes
> (lldb) platform process list
> 40 matching processes were found on "myhost.apple.com"
> ====== ====== ========== ======= ============================
> 46384  46139  gclayton   x86_64  lldb
> .....
> (lldb)
> There is much work to do, but there is a lot of support already in place to
> get remote debugging started.
> Let me know if you have any questions.
> Greg Clayton
I'll check some stuff with Linux and gdbserver and may have some more
questions afterwards. I managed to do some "remote" debugging with lldb,
with your help, which is one step closer to what I wanted.


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