[lldb-dev] add custom vendor commands

[Giusti, Valentina via lldb-dev]

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. 

> 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?

> - 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.

- Val 

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