[lldb-dev] gdb-remote to android gdbserver

[Greg Clayton]

The problem is we don't know the registers. GDB assumes that the GDB that is being used knows what registers are on the other side of the remote connection. New GDB binaries and GDBSERVER binaries are compiled for each target. LLDB has one binary for all systems. So LLDB expects to be able to query the GDBSERVER for the register information. LLDB has defined new packets to get this information. We have documented the packets we added:

svn cat http://llvm.org/svn/llvm-project/lldb/trunk/docs/lldb-gdb-remote.txt

I believe there is a way defined in the remote protocol to query for registers using the "qXfer" command with the "xmlRegisters" gdb feature. We haven't added support for this, but the "XML target description" format is missing information we need. The details on this are at:

https://sourceware.org/gdb/onlinedocs/gdb/Target-Description-Format.html#Target-Description-Format

It could also be easily extended to support giving us the information required.

So, in order to get things going you will need to do one of the following:
1 - add support for the qRegisterInfo packet (easiest)
2 - add a new "settings set" setting for the "gdb-remote" plug-in that contains a path to a register description file. The file format should be something parseable like XML and you would need to write a parser for it and parse the contents by adding a method to the  GDBRemoteDynamicRegisterInfo class (harder)
3 - If the current gdbserver for android does support the "XML target description", we would need to modify the GDBRemoteCommunicationClient class to be able to retrieve the information and parse the XML. You would then need to modify the gdbserver for android to add extra data we need to the register info (compiler register numbers for each register if one exists, DWARF register numbers, generic register info) (hardest)

I think option 1 or 2 would be the easiest.

Greg

On Aug 25, 2013, at 10:53 AM, Sebastien Metrot <meeloo at gmail.com> wrote:

> Hi, 
> 
> I have started to investigate connecting lldb to gdbserver running on an android device (arm). It connects correctly, I'm able to start the remote program and interrupt it but lldb doesn't permit me to access any data as it says the current frame is invalid:
> 
> mbp:NativeTest meeloo$ lldb ../../../ndk/samples/hello-gl2/libs/armeabi/libgl2jni.so 
> Current executable set to '../../../ndk/samples/hello-gl2/libs/armeabi/libgl2jni.so' (arm).
> (lldb) gdb-remote 
> error: gdb-remote [<hostname>:]<portnum>
> (lldb) gdb-remote 127.0.0.1:5039
> Process 12260 stopped
> * thread #1: tid = 0x2fe4, , stop reason = signal SIGTRAP
>     frame #0: 
> (lldb) frame variable
> error: invalid frame
> (lldb) continue
> Process 12260 resuming
> ---- Here I hit Ctrl+C
> Process 12260 stopped
> * thread #1: tid = 0x2fe4, , stop reason = signal SIGINT
>     frame #0: 
> (lldb) continue
> Process 12260 resuming
> (lldb) process interrupt 
> Process 12260 stopped
> * thread #1: tid = 0x2fe4, , stop reason = signal SIGINT
>     frame #0: 
> (lldb) register read
> error: invalid frame
> (lldb) process status
> Process 12260 stopped
> * thread #1: tid = 0x2fe4, , stop reason = signal SIGINT
>     frame #0: 
> 
> 
> Does anyone have already tried to do this kind of things? I'm trying to get it to work before moving to implementing android support in my program with the C++ API...
> 
> Thanks in advance,
> 
> S.
> 
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