[ktap] POC for ktap ffi support
- From: Qingping Hou <dave2008713@xxxxxxxxx>
- To: ktap@xxxxxxxxxxxxx, yichengq@xxxxxxxxxxxxxx, N@xxxxxxxxxxxxx: <jovi.zhangwei@xxxxxxxxx>
- Date: Sat, 02 Nov 2013 02:37:19 -0400
Hi all,
We made a POC for ktap ffi support. This feature makes it possible to
call into Kernel C function directly from inside ktap script.
A brief overview of current design:
* user define needed C symbols in ktap script (functions, structs, etc)
* C symbols get compiled into chunk and passed into ktap vm
* ktap vm generates ktap_ctype according to symbol information from
chunks and populates the global "C" table
* when ktap script calls "C.foo()", ktap vm detects that it's a FFI
function, and does following:
- sets up the hardware stack
- calls into the C function
- put back return value to ktap stack
Implementation of C function call is under interpreter/ffi/ffi_call.c,
including argument check, type conversion, stack setup and return value
handling.
Noted that in this POC, C symbol definitions are not compiled into ktap
chunk yet. Because we are still working on a C header parser. Currently,
we work around it by defining C symbols in ktap table and populate
global "C" table in runtime. That way we can focus on the FFI call
implementaion. This will be fixed in the third milestone.
Branch:
https://github.com/unihorn/ktap/tree/ffi-cp1
Support:
- x86_64 machine
- int, long, longlong and void type
- kernel functions that are defined in C table in script
- implicit type conversion between ctypes and ktap types
Test:
New test script is under test/ffi/
```
# ./ktap test/ffi/cdef.kp
```
Plan:
https://github.com/ktap/ktap/wiki/FFI-Support
Please feel free to point out any problem in the design so we fix it as
soon as possible :)
Regards,
Yicheng & Qingping
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