Goal
The main goal of llvmcpy is to provide Python bindings for the LLVM project
that are fast and require the lowest possible maintainance effort. To achive
this, we use CFFI to parse the (slightly adapted) header files for the LLVM-C API_ and automatically generate a set of classes and functions to interact with
them in a Pythonic way.
This project is in an early stage, but allows you to run the following code::
import sys
from llvmcpy.llvm import *
buffer = create_memory_buffer_with_contents_of_file(sys.argv[1])
context = get_global_context()
module = context.parse_ir(buffer)
for function in module.iter_functions():
for bb in function.iter_basic_blocks():
for instruction in bb.iter_instructions():
instruction.dump()
It has been tested with LLVM 3.4, 3.8 and 3.9. Supporting older and newer
versions of the LLVM-C API_ should be basically effortless.
To try it out install LLVM and get llvmcpy using pip::
sudo apt-get install llvm
pip install llvmcpy
Naming of the generated classes/functions
The basic idea behind this project is to take the LLVM-C API_ function, create
a class for each data type and create a method for that class for each function
in the API taking an argument of that data type as first argument.
This means that the following functions::
LLVMModuleRef LLVMCloneModule (LLVMModuleRef M)
Will become::
class Module(object):
def clone(self):
# ...
Note the change in the case. Use help(Module.clone) to see which LLVM-C API_ function a certain method is using.
Each class in llvmcpy is basically a wrapper around a pointer to an LLVM
object.
If an API function doesn't take an LLVM object as a first argument, it will be
part of the llvm module. Moreover, we also have some also generated properties
and generators for certain well known patterns in the API.
:Properties: For each function starting with LLVMGet or LLVMSet in the
LLVM-C API_, we generate a property. For example, consider the
following two functions::
void LLVMSetValueName (LLVMValueRef Val, const char *Name)
const char* LLVMGetValueName(LLVMValueRef Val)
In `llvmcpy` the `Get`/`Set` prefixes disappear, along with `Value`
(the name of the class) and you can use them as properties of the
`Value` class, e.g.::
my_value.name = "sum"
print my_value.name
:Generators: The LLVM-C API_ has a recurrent pattern which allows you to
navigate through the hierarchy of its class hierarchy, i.e. the
pair of LLVMGetSomething and LLVMGetNextSomething
functions. Something can be Function, BasicBlock and so
on. llvmcpy identifies these patterns and produces a generator
method which allows you to iterate over these objects in a Pythonic
way::
for function in module.iter_functions():
for bb in function.iter_basic_blocks():
for instruction in bb.iter_instructions():
# ...
Where are my bindings?
Bindings are automatically generated in a lazy way. Multiple installations of
LLVM are supported, just set the LLVM_CONFIG environment variable to the
llvm-config program in the bin/ directory of your LLVM installation and
everything should work fine.
The bindings are generated in a Python script which is stored in
$XDG_CACHE_DIR/llvmcpy/ (typically ~/.cache/) in a directory whose name
is obtained by hashing the full path of the output of llvm-config --prefix
concatenated with the LLVM version number. For example, for LLVM 3.9.0 installed
in /usr you'll find the API bindings in
~/.cache/llvmcpy/7fea08f2e9d5108688f692e686c8528b914eda563e7069b25ef18c49ba96d7f2-3.9.0.
To generate the bindings a working C preprocessor must be available in the
system. By default cpp (the C preprocessor part of GCC) is used. If it's not
available we check if clang is available in the LLVM installation and use it.
License and credits
This project is developed and maintained by Alessandro Di Federico
(ale+llvmcpy@clearmind.me) as a part of the rev.ng_ project, and it's released
under the MIT license.
.. _rev.ng: https://rev.ng/
.. _LLVM-C API: http://llvm.org/docs/doxygen/html/group__LLVMC.html