uACPI

A portable and easy-to-integrate implementation of the Advanced Configuration and Power Interface (ACPI).

Warning

Not yet ready for production use! While the project is mostly feature-complete, it is still under active development. Public API may change, get added or removed without notice. Thread safety is currently lacking, see #74 for more info & progress.

Features

• A fast and well-tested AML interpreter optimized to use very little stack space
• NT-compatible on a fundamental level (see examples)
• Very easy to integrate (ships with own overridable standard library implementation)
• Highly flexible and configurable (optional sized frees, reduced-hw-only mode, etc.)
• A fairly advanced event subsystem (GPE/fixed, wake, implicit notify, AML handlers)
• Table management API (search, dynamic installation/loading, overrides, etc.)
• Operation region subsystem (user handlers, builtins for common types)
• Sleep state management (transition to any S state, wake vector programming)
• PCI routing table retrieval & interrupt model API
• Device search API
• Resource subsystem supporting every resource defined by ACPI 6.5
• Interface & feature management exposed via _OSI
• Client-defined Notify() handlers
• Firmware global lock management (_GL, locked fields, public API)
• GAS read/write API

Why would I use this over ACPICA?

Whilst ACPICA is an old and battle-tested project, it still has some fundamental issues that make it very far from perfect or ideal.

TLDR:

• Much better compatibility with the Windows NT object implicit-cast semantics than ACPICA
• AML reference semantics 100% compatible with the Windows AML interpreter, including edge cases.
• A more sophisticated and safe object lifetime tracking without extra overhead (AML that would crash the NT interpreter works just fine!)
• No recursion when doing dynamic table loads from AML (Load/LoadTable)
• Unlike ACPICA, uACPI doesn't try to work around AML code designed for the Windows NT ACPI driver, instead, it embraces it
• No design flaws preventing true multi-threaded uses without the global interpreter lock

More detailed overview

Expressions within package:

Method (TEST) {
    Local0 = 10
    Local1 = Package { Local0 * 5 }
    Return (DerefOf(Local1[0]))
}

// ACPICA: AE_SUPPORT, Expressions within package elements are not supported
// Windows, uACPI: Local0 = 50
Local0 = TEST()

Packages outside of a control method:

// ACPICA: internal error
// Windows, uACPI: ok
Local0 = Package { 1 }

Reference rebind semantics:

Local0 = 123
Local1 = RefOf(Local0)

// ACPICA: Local1 = 321, Local0 = 123
// Windows, uACPI: Local1 = reference->Local0, Local0 = 321
Local1 = 321

Increment/Decrement:

Local0 = 123
Local1 = RefOf(Local0)

// ACPICA: error
// Windows, uACPI: Local0 = 124
Local1++

Multilevel references:

Local0 = 123
Local1 = RefOf(Local0)
Local2 = RefOf(Local1)

// ACPICA: Local3 = reference->Local0
// Windows, uACPI: Local3 = 123
Local3 = DerefOf(Local2)

Implict-cast semantics:

Name (TEST, "BAR")

// ACPICA: TEST = "00000000004F4F46"
// Windows, uACPI: TEST = "FOO"
TEST = 0x4F4F46

Buffer size mutability:

Name (TEST, "XXXX")
Name (VAL, "")

// ACPICA: TEST = "LONGSTRING"
// Windows, UACPI: TEST = "LONG"
TEST = "LONGSTRING"

// ACPICA: VAL = "FOO"
// Windows, UACPI: VAL = ""
VAL = "FOO"

Returning a reference to a local object:

Method (TEST) {
    Local0 = 123

    // Use-after-free in ACPICA, perfectly fine in uACPI
    Return (RefOf(Local0))
}

Method (FOO) {
    Name (TEST, 123)

    // Use-after-free in ACPICA, object lifetime prolonged in uACPI (node is still removed from the namespace)
    Return (RefOf(TEST))
}

There's even more examples, but this should be enough to demonstrate the fundamental differences in designs.

Integrating into a kernel

1. Add uACPI sources & include directories into your project

If you're using CMake

Simply add the following lines to your cmake:

include(uacpi/uacpi.cmake)

target_sources(
    my-kernel
    PRIVATE
    ${UACPI_SOURCES}
)

target_include_directories(
    my-kernel
    PRIVATE
    ${UACPI_INCLUDES}
)

If you're using Meson

Add the following lines to your meson.build:

uacpi = subproject('uacpi')

uacpi_sources = uacpi.get_variable('sources')
my_kernel_sources += uacpi_sources

uacpi_includes = uacpi.get_variable('includes')
my_kernel_includes += uacpi_includes

Any other build system

• Add all .c files from source into your target sources
• Add include into your target include directories

2. Implement/override platform-specific headers

uACPI defines all platform/architecture-specific functionality in a few headers inside include/uacpi/platform

All of the headers can be "implemented" by your project in a few ways:

• Implement the expected helpers exposed by the headers
• Replace the expected helpers by your own and override uACPI to use them by defining the respective UACPI_OVERRIDE_X variable. In this case, the header becomes a proxy that includes a corresponding uacpi_x.h header exported by your project.

Currently used platform-specific headers are:

• arch_helpers.h - defines architecture/cpu-specific helpers & thread-id-related interfaces
• compiler.h - defines compiler-specific helpers like attributes and intrinsics. This already works for MSVC, clang & GCC so you most likely won't have to override it.
• atomic.h - defines compiler-specific helpers for dealing with atomic operations. Same as the header above, this should work out of the box for MSVC, clang & GCC.
• libc.h - an empty header by default, but may be overriden by your project if it implements any of the libc functions used by uACPI (by default uACPI uses its own implementations to be platform-independent and to make porting easier). The internal implementation is just the bare minimum and not optimized in any way.
• types.h - typedefs a bunch of uacpi-specific types using the stdint.h header. You don't have to override this unless you don't provide stdint.h.

3. Implement kernel API

uACPI relies on kernel-specific API to do things like mapping/unmapping memory, writing/reading to/from IO, PCI config space, and many more things.

This API is declared in kernel_api.h and is implemented by your kernel.

4. Initialize uACPI

That's it, uACPI is now integrated into your project.

You should proceed to initialization.
Refer to the uACPI page on osdev wiki to see a snippet for basic initialization, as well as some code examples of how you may want to use certain APIs.

All of the headers and APIs defined in uacpi are public and may be utilized by your project.
Anything inside uacpi/internal is considered private/undocumented and unstable API.

Developing and contributing

Most development work is fully doable in userland using the test runner.

Setting up an IDE:

Simply open tests/runner/CMakeLists.txt in your favorite IDE.

For Visual Studio:

cd tests\runner && mkdir build && cd build && cmake ..

Then just simply open the .sln file generated by cmake.

Running the test suite:

./tests/run_tests.py

If you want to contribute:

• Commits are expected to be atomic (changing one specific thing, or introducing one feature) with detailed description (if one is warranted for), an S-o-b line is welcome
• Code style is 4-space tabs, 80 cols, the rest can be seen by just looking at the current code

All contributions are very welcome!

License

uACPI is licensed under the MIT License.
The full license text is provided in the LICENSE file inside the root directory.