# VC4CL **Repository Path**: deadship/VC4CL ## Basic Information - **Project Name**: VC4CL - **Description**: No description available - **Primary Language**: Unknown - **License**: MIT - **Default Branch**: master - **Homepage**: None - **GVP Project**: No ## Statistics - **Stars**: 0 - **Forks**: 0 - **Created**: 2020-06-05 - **Last Updated**: 2020-12-19 ## Categories & Tags **Categories**: Uncategorized **Tags**: None ## README # Status [![CircleCI](https://circleci.com/gh/doe300/VC4CL.svg?style=svg)](https://circleci.com/gh/doe300/VC4CL) **NOTE: VC4CL will NOT work with Raspberry Pi 4, since it has an incompatible GPU!** # VC4CL **VC4CL** is an implementation of the **OpenCL 1.2** standard for the VideoCore IV GPU (found in all Raspberry Pi models). The implementation consists of: * The **VC4CL** OpenCL runtime library, running on the host CPU to compile, run and interact with OpenCL kernels. * The **[VC4C](https://github.com/doe300/VC4C)** compiler, converting OpenCL kernels into machine code. This compiler also provides an implementation of the OpenCL built-in functions. * The **[VC4CLStdLib](https://github.com/doe300/VC4CLStdLib)**, the platform-specific implementation of the OpenCL C standard library, is linked in with the kernel by **VC4C** ## OpenCL-Support The VC4CL implementation supports the **EMBEDDED PROFILE** of the [OpenCL standard version 1.2](https://www.khronos.org/registry/OpenCL/specs/opencl-1.2.pdf). Additionally the [`cl_khr_icd` extension](https://www.khronos.org/registry/OpenCL/specs/opencl-1.2.pdf) is supported, to allow VC4CL to be found by an installable client driver loader (**ICD**). This enables VC4CL to be used in parallel with another OpenCL implementation, e.g. [pocl](https://github.com/pocl/pocl), which executes OpenCL code on the host CPU. The OpenCL version 1.2 was selected as target standard version, since it is the last version of the OpenCL standard where all mandatory features can be supported. VC4CL supports the **EMBEDDED PROFILE** of the OpenCL-standard, which is a trimmed version of the default **FULL PROFILE**. The most notable features, which are not supported by the VC4CL implementation are images, the `long` and `double` data-types, device-side `printf` and partitioning devices. See [RuntimeLibrary](https://github.com/doe300/VC4CL/wiki/RuntimeLibrary) for more details of (not) supported features. ## VideoCore IV GPU The VideoCore IV GPU, in the configuration as found in the Raspberry Pi models, has a theoretical maximum performance of **24 GPFLOS** and is therefore very powerful in comparison to the host CPU. The GPU (which is located on the same chip as the CPU) has 12 cores, able of running independent instructions each, supports a SIMD vector-width of 16 elements natively and can access the RAM directly via DMA. ## Required software - A C++14-capable compiler (e.g. GCC 6.3 or clang from the Raspbian repositories) - The [VC4C](https://github.com/doe300/VC4C) compiler to compile OpenCL C-code - The Raspbian development files (available in the official Raspbian repository as `sudo apt-get install libraspberrypi-dev`) - The Khronos ICD Loader (available in the official Raspbian repository as `sudo apt-get install ocl-icd-opencl-dev ocl-icd-dev`) for building with ICD-support (e.g. allows to run several OpenCL implementations on one machine) - The OpenCL headers in version >= 1.2 (available in the Raspbian repositories as `sudo apt-get install opencl-headers`) - The Raspberry Pi [firmware](https://github.com/raspberrypi/firmware) GPU-side and host-side binaries as well as the [mailbox kernel module](https://github.com/raspberrypi/linux). These are already provided by default on Raspbian OS. For other Linux distributions, see [here](https://github.com/doe300/VC4CL/issues/53). ## Build The following configuration options are available in CMake: - `BUILD_TESTING` toggles building of test program (when configured, can be built with `make TestVC4CL`) - `CMAKE_BUILD_TYPE` set to *Debug*, *Release*, *asan*, *tsan* or *usbsan* to build for the given debug/release mode or with sanitizers enabled - `CROSS_COMPILE` toggles whether to cross-compile for the Raspberry Pi. NOTE: The [Raspberry Pi cross-compiler](https://github.com/raspberrypi/tools) is no longer supported! - `CROSS_COMPILER_PATH` sets the root path to the Raspberry Pi cross compiler (.g. `arm-linux-gnueabihf-g++-6`) - `INCLUDE_COMPILER` whether to include the [VC4C](https://github.com/doe300/VC4C) compiler. For the compiler to be actually included, the VC4C header and library needs to be found too - `VC4C_HEADER_PATH` sets the path to the VC4C include headers, defaults to `../VC4C/include/VC4C.h` or `lib/vc4c/include/VC4C.h` - `VC4CC_LIBRARY` sets the path to the VC4C compiler library, defaults to `../VC4C/build/libVC4CC.xxx` or `lib/vc4c/build/libVC4CC.xxx` - `BUILD_ICD` toggles whether to build with support for the Khronos ICD loader, requires the ICD loader to be installed system-wide - `IMAGE_SUPPORT` toggles whether to enable the very experimental image-support - `REGISTER_POKE_KERNELS` toggles the use of register-poking to start kernels (if disabled, uses the mailbox system-calls). Enabling this increases performance up to 10%, but may crash the system, if any other application accesses the GPU at the same time! ## Khronos ICD Loader The Khronos ICD Loaders allows multiple OpenCL implementation to be used in parallel (e.g. VC4CL and [pocl](https://github.com/pocl/pocl)), but requires a bit of manual configuration: Create a file `/etc/OpenCL/vendors/VC4CL.icd` with a single line containing the absolute path to the VC4CL library. The program clinfo can be used to test, whether the ICD loader finds the VC4CL implementation. **Note**: the program version in the official Raspbian repository is too old and has a bug (see [fix](https://github.com/Oblomov/clinfo/commit/4728656fcb1ff5d506b8ef2103af83ce11ceae36)), so it must be compiled from the [github](https://github.com/Oblomov/clinfo) repository. ## Security Considerations Because of the DMA-interface which has no MMU between the GPU and the RAM, code executed on the GPU can **access any part of the main memory**! This means, an OpenCL kernel could be used to read sensitive data or write into kernel memory! **Therefore, any program using the VC4CL implementation must be run as root!** ## Debug Since this software is still in development, some functionality might not work. For curious users or to be able to provide more information for bugs, additional debug information can be generated if desired. To generate debug information, set the `VC4CL_DEBUG` environment variable to one (or multiple, separated by commas) of the following strings: - `api` enables logging OpenCL API calls, parameters and non-success errors to the standard output - `code` enables dumping OpenCL C (or IR) source code as well as generated VC4C binary code into temporary files for the compilation functions - `syscall` enables logging detailed information for syscalls (e.g. mailbox) to the standard output - `execution` enables logging of detailed kernel execution information (parameters, execution cycle, return codes) to the standard output - `events` enables logging of asynchronous event processing information to the standard output - `objects` enables logging of lifetime begin/end and leaks of OpenCL API objects to the standard output - `all` enables all above logging modes