[lldb-dev] LLDB for Android initiative

Tue Nov 19 07:50:35 PST 2013

Thanks for the reply, Matt!

CIL

On Mon, Nov 18, 2013 at 11:15 PM, Matt Kopec <kopec.m at gmail.com> wrote:

> Hi Todd,
>
> It's great that you are looking at lldb!
>
>
Looking forward to it :-)

> In general, it looks like many of the things you want to do with lldb
> right now you can, to some extent. I don't think there are too many people
> looking at lldb for Linux right now as the Linux buildbots are failing so
> there may be bugs introduced as time goes on.
>

Sounds like a good area for me to start investigating.

> Also, the only real way to do some remote debugging with Linux today is to
> use gdbserver. The major feature lldb for Linux (and useful for lldb in
> general) would benefit from is a "lldbserver" that works for all platforms.
>
>
Okay, thanks.  More on this below.

> I've also provided some comments inlined below...
>
> Thanks,
> Matt
>
> On Mon, Nov 18, 2013 at 11:40 PM, Todd Fiala <tfiala at google.com> wrote:
>
>> Hi all!
>>
>> I'm starting up an effort to get LLDB running on Android.  I just wanted
>> to reach out, say hi, and give you an outline of how I'm thinking about
>> attacking this effort.  I'm looking for feedback, so please fire away if
>> you have any suggestions or comments!
>>
>>  I'm thinking of attacking the effort in stages, looking something like
>> this:
>>
>> 1. Get LLDB up and running against a local Linux x86 process.
>>
>>  It looks like many aspects of this already work.  I've heard there might
>> be some rough edges around core dump support, DWARF 4/5 support, and
>> possibly some optimized debug info support on the clang side, so any work
>> here might touch those areas.
>>
>> I see we have what looks like 2 buildbots dedicated to building lldb in
>> linux scenarios:
>>
>> http://lab.llvm.org:8011/builders/lldb-x86_64-debian-clang
>>  http://lab.llvm.org:8011/builders/lldb-x86_64-linux
>>
>> Android currently builds linux host tools as 32-bit.  Both of those
>> buildbots above appear to be 64-bit. I'd love to get the equivalent of an
>> Ubuntu 12.04 LTS x64 buildbot building a 32-bit LLDB executable.  How can I
>> go about setting that up?
>>
>>
> > You can provide your own buildbot using the instructions here:
> http://llvm.org/docs/HowToAddABuilder.html
>
>
Great, thanks for pointing me to that!

> 2. Get the LLDB remote solution up and running against a remote Linux x86
>> process.
>>
>> Here we get to the first high-level question mark: do we continue to use
>> gdbserver, use debugserver, or base something on lldb-platform?  I haven't
>> dug into this yet.  I've heard some thoughts on this topic, such as (a)
>> LLDB has extended the gdb remote protocol and offers some benefits over
>> using gdbserver, (b) debugserver is currently very part-specific and might
>> be a painful way to go in the short term (but I haven't heard comments on
>> the longer-term potential benefits of toughing through that), and (c)
>> lldb-platform is a reasonable starting point and has been used to get some
>> traction bringing up LLDB on other chipsets.  Like in (1), I'll want to set
>> up a build bot that builds and runs remote tests in this environment.
>>
>> Any thoughts on this?
>>
>> > You can use gdbserver with lldb today. Though, there are packets lldb
> supports that gdb doesn't. For instance, lldb figures out the remote server
> register set through special packets. This works with debugserver
> (debugserver is mac/ios only) but not with gdbserver. In the gdbserver
> case, I believe lldb will default to some version of ARM registers for the
> register set. So, connecting to gdbserver you may need to know the remote
> registers beforehand and provide that to lldb (more details here
> http://llvm.org/viewvc/llvm-project?view=revision&revision=192646).
>

Thanks for that link.  Android uses gdbserver for the current native
debugging support via gdb.  I'll be checking how far that gets me with a
linux host top of tree lldb vs. a few stock Nexus devices.

> Other then this, my understanding is that lldb works reasonably well with
> gdbserver. There are other benefits of debugserver over gdbserver today
> such as better network/packet performance though I haven't seen the numbers
> myself.
>
>
That was the first draw for looking at debugserver --- I'm not aware of all
the details yet and wanted to dig into this more, but I had heard that lldb
had been extending the gdb remote protocol and had adjusted some aspects to
make it a more efficient protocol.  If anybody has more details on this one
way or the other, that would be great to hear.

> There was a proposal made on the mailing list a few months ago with
> regards to implementing platform-independent remote debugging. That
> proposal is found here:
> http://www.mail-archive.com/lldb-dev@cs.uiuc.edu/msg02164.html. It's
> fairly detailed but in essence the idea was that if debug support was added
> for, say, FreeBSD on ARM (in one place), then both native and remote
> debugging would work for this platform immediately. So, among other things
> suggested in the proposal, a new "lldbserver" which supports the current
> packets debugserver does but is platform independent. Overall, this will
> require effort and I don't think anyone is working on it. It would be great
> to have!
>
>

Excellent - I'll have a look at the proposal.  This certainly sounds like
it would be great to kill two birds with one stone.

> 3. Get the LLDB remote solution up and running against a remote Linux ARM
>> system.
>>
>> The idea being that it will be easier for me to poke around on the Linux
>> ARM system than it would be to go straight for the Android device or
>> emulator, but gets me working against an ARM system, one step closer to a
>> typical Nexus device.  And helps out ARM Linux remote support in the
>> process (if there are any weak spots).  I don't know yet what the scope of
>> work here might entail.  Similar to (2), I'll want to set up a build bot
>> that builds and runs remote tests in this environment as well.
>>
> > If you have a gdbserver built for Linux ARM this might just work. You'll
> only be able to poke around on the 'gdb-remote plugin' side of lldb in this
> case. This plugin is used independent of what gdbserver or debugserver you
> are connecting to and works well.
>
>

Thanks!

> 4. Getting LLDB remote solution up and running against an Android ARM
>> device.
>>
>> > Same as above, the gdbserver that comes with the Android NDK should
> work (maybe it will even work in the Linux case?).
>
>
>> 5. Either directly implement or make it straightforward for Android
>> vendors to fill in anything necessary to use our remote solution on other
>> Android hardware.
>>
>> > Only thing I can think of here is supporting new x86_64/ARM/MIPS
> registers as they come along.
>
> That would be great if the majority of my team's effort was spent
improving LLDB rather than maintaining architecture-specific support :-)

> I look forward to working with the LLDB community on this effort!
>>  Suggestions or comments are appreciated.
>>
>> Sincerely,
>> Todd Fiala
>>
>> _______________________________________________
>> lldb-dev mailing list
>> lldb-dev at cs.uiuc.edu
>> http://lists.cs.uiuc.edu/mailman/listinfo/lldb-dev
>>
>>
>
Thanks again for all the comments, Matt!
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