| # Runtime Platform Abstraction Layer (PAL) |
| |
| The ExecuTorch _Platform Abstraction Layer_ (PAL) provides a way for execution |
| environments to override operations like: |
| - Getting the current time. |
| - Printing a log statement. |
| - Panicking the process/system. |
| |
| The PAL function declarations are in |
| [`executorch/runtime/platform/platform.h`](https://github.com/pytorch/executorch/blob/main/runtime/platform/platform.h). |
| |
| ## Overriding the default PAL |
| |
| The default PAL implementation is in |
| [`executorch/runtime/platform/target/Posix.cpp`](https://github.com/pytorch/executorch/blob/main/runtime/platform/target/Posix.cpp). |
| It uses `std::chrono::steady_clock` for the time, prints log messages to |
| `stderr`, and makes other default assumptions. |
| |
| But, if they don't work for your system, you can override the default PAL by: |
| - Including |
| [`executorch/runtime/platform/platform.h`](https://github.com/pytorch/executorch/blob/main/runtime/platform/platform.h) |
| in one of your application's `.c` or `.cpp` files. |
| - Defining an implementation of one or more of the `et_pal_*()` functions. |
| |
| No build system changes necessary. The default PAL functions are weak symbols, |
| so providing your own strong-symbol definition will override them at link time. |
| |
| ## Minimal PAL |
| |
| If you run into build problems because your system doesn't support the functions |
| called by `Posix.cpp`, you can instead use the no-op minimal PAL at |
| [`executorch/runtime/platform/target/Minimal.cpp`](https://github.com/pytorch/executorch/blob/main/runtime/platform/target/Minimal.cpp) |
| by building with the `buck2` flag `-c executorch.pal_default=minimal`. This will |
| avoid calling `fprintf()`, `std::chrono::steady_clock`, and anything else that |
| `Posix.cpp` uses. But since the `Minimal.cpp` `et_pal_*()` functions are no-ops, |
| you will need to override all of them. |
