runtime-platform-abstraction-layer.md

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.

Overriding the default PAL

The default PAL implementation is in executorch/runtime/platform/default/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 in one of your application's .c or .cpp files.
• Defining an implementation of one or more of the et_pal_*() functions.

The default PAL functions are weak symbols, so providing your own strong-symbol definition can override them at link time. To ensure that your definitions take precedence, you may need to ensure that the strong definitions precede the weak definitions in the link order.

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/default/minimal.cpp by passing -DEXECUTORCH_PAL_DEFAULT=minimal to cmake. 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.