Python bindings for LLVM auto-generated from the LLVM-C API
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) 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 3.8 and 3.9. Supporting older and newer versions of the LLVM-C API should be basically effortless.
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)
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.
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
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.