[lldb-dev] LLDB porting docs

[Greg Clayton]

On Jan 19, 2012, at 2:51 AM, Mool Chand Tyagi wrote:

>> Does LLVM support the VLIW architecture? 
> 
> Yes, the LLVM supports VIW architecture, the compiler tool chain for which i 
> am planning to port LLDB is based on LLVM.

That is good.

>> What file format will the executables for VLIW be using? Hopefully ELF32 of 
> ELF64? 
> 
> Our executable file format is ELF32.

Great!

> 
> 
>> The Process plug-in is the part that connects to your remote system. If you 
>> are using a JTAG library that can speak the GDB remote protocol, you might 
>> not have to write a Process plug-in. how do you communicate and debug your 
>> executables? Do you have a running OS where lldb is running in user space on 
>> that OS? Will you be doing remote debugging? 
> 
> We plan for remote debugging, we plan to modify the existing target simulator 
> to communicate with ported LLDB. In that case, LLDB may work as a client 
> asking for information from a Target simulator, which is considered as a 
> server.
> 
> I hope i answered your doubts. If you have further question please let me 
> know, i will explore and try to answer.
> 
> Moreover, i observed that LLDB supports remote debugging, however, i do not 
> know the details. If possible please share some information about remote 
> debugging supported in LLDB.

We use the GDB remote protocol for debugging with extensions to allow for discoverability. We also have some packets that implement a remote "platform" which would allow you to list remote processes, attach or launch processes and more built into the GDB remote protocol. The platform stuff is still a work in progress, but we eventually plan to flesh everything out and perfect it.

The GDB remote protocol is documented on the web, and the LLDB specific extensions are documented in:

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

Let me know if you have any other questions.
> 
> Regards,
> Mool Chand Tyagi
> 
> 
> Greg Clayton <gclayton <at> apple.com> writes:
> 
>> 
>> There currently aren't any documents. I need to sit down and write them 
> sometime soon.
>> 
>> A few questions:
>> 
>> The big one: Does LLVM support the VLIW architecture? If not we won't have a 
> way to evaluate expressions, or
>> disassemble. This would be a show stopper if there is no LLVM support.
>> 
>> What file format will the executables for VLIW be using? Hopefully ELF32 of 
> ELF64? If so, then there is no
>> work to be done on the ObjectFile parser side.
>> 
>> Is this for bareboard or OS development?
>>  If bareboard, no work needs to be done on the DynamicLoader plug-in side.
>>  If OS developtment where you will have shared libraries loading/unloading 
> then you will need to write a
>> DynamicLoader plug-in for your OS or kernel.
>> 
>> The plug-ins you will then need to subclass and create would be:
>> - lldb_private::Platform
>> - lldb_private::ABI
>> - lldb_private::Process
>> 
>> The Platform plug-in helps answer questions like "where is the 
> file /usr/lib/libfoo.so locally on this
>> machine" when you are doing a debug session. It also helps with locating 
> executables in bundles, and
>> selecting the right architecture from executables if you have an executable 
> bundle or binary that
>> contains one or more architecture versions.
>> 
>> The ABI plug-in helps us to be able to find out where arguments are passed 
> when making function calls and when
>> looking for return values from function calls. It also helps define a whole 
> bunch of other things that are
>> defined by the ABI like which registers are spilled/volatile/etc.
>> 
>> The Process plug-in is the part that connects to your remote system. If you 
> are using a JTAG library that can
>> speak the GDB remote protocol, you might not have to write a Process plug-
> in. how do you communicate and
>> debug your executables? Do you have a running OS where lldb is running in 
> user space on that OS? Will you be
>> doing remote debugging? If so, how does one communicate with your remote 
> debug session?
>> 
>> Greg Clayton
>> 
>> On Jan 4, 2012, at 10:31 PM, Mool Chand Tyagi wrote:
>> 
>>> Hi, 
>>> 
>>> I am looking forward to use LLDB to port to a VLIW architecture, can 
> anyone help me by providing some
>> pointers to documents or Readme texts.. ?
>>> 
>>> thanks and regards,
>>> tyagi
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
>>> 
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>> 
> 
> 
> 
> 
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