[lldb-dev] add custom vendor commands

[Greg Clayton via lldb-dev]

> On Oct 18, 2016, at 7:48 AM, Giusti, Valentina <valentina.giusti at intel.com> wrote:
> 
> Hi Greg,
> 
> Thanks a lot for your reply, please find below my answers.
> 
>> You can install new python commands that can do the job to work out the
>> details.
>> 
>> http://lldb.llvm.org/python-reference.html
>> 
>> See the section named "CREATE A NEW LLDB COMMAND USING A PYTHON
>> FUNCTION".
>> 
>> You can basically install a new "intel" command and parse all of the options
>> "show mpx-bounds ..." or "set mpx-bounds ..." from within this new command.
>> You can use the public LLDB API to look through the process and do things. Let
>> me know if you need any help with this. There is also a API to add custom
>> commands from C++ plug-ins. Enrico Granata did this work and can answer
>> more questions on that. Either way, both commands (python and C++ plug-ins)
>> have access to the public API for LLDB, so the code you will write will use the
>> same API. So I would stick with python for now to get things working.
>> 
> 
> I think I would rather start right away with the C++ approach. If I understand correctly, it means to create a specific Intel plugin under the directory source/Plugins and use the LLDB API to add the custom command. 

That is one way to do this, but any change you make will require a recompile of LLDB. 

The only external plug-ins we currently have with LLDB are for adding commands. See the following code in our test suite where $(trunk) is the root of your LLDB checkout:

$(trunk)/packages/Python/lldbsuite/test/functionalities/plugins/commands

This show you how to compile a C++ plug-in that will be loaded by LLDB if it is placed in the right plug-in location.  So this would allow you to distribute a plug-in that can work with existing released LLDB in case you care to do so.

> 
>> Some questions for you:
>> - How do plan on detecting that you have an intel processor?
> 
> I thought of checking if the target architecture is either llvm::Triple::x86 or llvm::Triple::x86_64. Do you think there is a better approach to this?

I guess just checking for the "BNDCFGU" register is what you will need to do?

> 
>> - Do you need access to any process registers? If so, are these registers thread
>> specific? Are these registers available currently on linux and MacOS?
> 
> I only need to access the MPX configuration register, BNDCFGU. As far as I know, MacOS doesn't have MPX support, so I also didn't implement the MPX support for MacOS in LLDB, which means it is only available in Linux at the moment.
> 
>> - How do you locate the BT? (or do you even need to?). Is there symbol? Can
>> you extract all values in the bounds table once you locate it?
>> 
> 
> The bound tables are allocated contiguously in the process memory, starting from the Bound Directory address which is stored in the BNDCFGU register. Therefore, in the plugin I only need to access this register, do the appropriate calculations and then access the process memory to get the requested bound table entry.

Great. This sounds easy to do. Just decide if you prefer a built in command or to create an external command shared library plug-in and you are all set to go!

Greg

> 
> - Val 
> 
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