ACPI Debugging (1) - ACPI AML Runtime Debugger in Ubuntu 18.04 (x64)

ACPICA is an open-source project that provides an operating system (OS)-independent reference implementation. It also contains a list of utilities such as ASL compiler (iasl), acpiexec (an AML emulator) and so on. However, debugging AML on Linux in runtime wasn't provided in ACPICA ... not until Linux Kernel 4.13.

Enabling AML Debugging

The aml-debugger.txt, the instruction for enabling AML runtime debugger, is available at Documentation/acpi/ in Linux kernel source code. In short, two things are required for AML runtime debugging

• Enable AML debugging (CONFIG_ACPI_DEBUGGER=y & CONFIG_ACPI_DEBUGGER_USER=m) when compiling Linux kernel

• Compile an utility, acpidbg from Linux kernel (I uploaded a copy here)

While compiling a custom-build kernel is nothing new to kernel developers, it is often inconvenient for system firmware / BIOS developers who need to verify ACPI AML implementation in their firmware. Fortunately, Ubuntu 18.04 (x64) and later enable these config by default, and one can simply execute acpidbg on Ubuntu 18.04 - even on Ubuntu Live from USB too!

Running AML Debugging

Executing acpidbg on Ubuntu 18.04 (x64) is straight-forward
$ sudo ./acpidbg -

and "help" shows a list supported commands
- help General-Purpose Commands: ... ... Namespace Access Commands: ... ... Control Method Execution Commands: ... ...

Examples

acpidbg is particularly handy when one needs to evaluate any ACPI AML objects during runtime - especially ones that change under different conditions. This may be explained by some examples below:

Example 1 - To determine AC power status in runtime.

1. Find _PSR objects
2. Evaluate _PSR when AC is disconnected
3. Evaluate _PSR when AC is connected.

- find _PSR \_SB.PCI0.LPC.EC.AC._PSR Method 00000000c53d0a47 01 Args 0 Len 0023 Aml 00000000eab88cb2 - execute \_SB.PCI0.LPC.EC.AC._PSR Evaluating \_SB.PCI0.LPC.EC.AC._PSR Evaluation of \_SB.PCI0.LPC.EC.AC._PSR returned object 00000000c46fa555, external buffer length 18 [Integer] = 0000000000000000 - execute \_SB.PCI0.LPC.EC.AC._PSR Evaluating \_SB.PCI0.LPC.EC.AC._PSR Evaluation of \_SB.PCI0.LPC.EC.AC._PSR returned object 00000000c46fa555, external buffer length 18 [Integer] = 0000000000000001

acpidbg also works with complex objects such as packages.
Example 2 - To determine battery information and status.

1. Find _BIF and _BST objects
2. Evaluate _BIF and _BST objects (note _BST changes dynamically).

- find _BIF \_SB.PCI0.LPC.EC.BAT0._BIF Method 00000000817541c3 01 Args 0 Len 0040 Aml 000000009abb252e - execute \_SB.PCI0.LPC.EC.BAT0._BIF Evaluating \_SB.PCI0.LPC.EC.BAT0._BIF Evaluation of \_SB.PCI0.LPC.EC.BAT0._BIF returned object 00000000c46fa555, external buffer length 170 [Package] Contains 13 Elements: [Integer] = 0000000000000000 [Integer] = 000000000000ABE0 [Integer] = 0000000000009E34 [Integer] = 0000000000000001 [Integer] = 0000000000003B60 [Integer] = 00000000000007E9 [Integer] = 00000000000000C8 [Integer] = 0000000000000001 [Integer] = 0000000000000001 [String] Length 07 = "00HW027" [String] Length 05 = " 409" [String] Length 03 = "LiP" [String] Length 03 = "SMP" - find _BST \_SB.PCI0.LPC.EC.BAT0._BST Method 00000000ed98c5ba 01 Args 0 Len 001D Aml 00000000a48eaeb6 - execute \_SB.PCI0.LPC.EC.BAT0._BST Evaluating \_SB.PCI0.LPC.EC.BAT0._BST Evaluation of \_SB.PCI0.LPC.EC.BAT0._BST returned object 00000000c46fa555, external buffer length 78 [Package] Contains 4 Elements: [Integer] = 0000000000000001 [Integer] = 00000000000010C6 [Integer] = 00000000000088B8 [Integer] = 0000000000003FC9

acpidbg can decode bit fields and save time on counting bits. Try to run acpidbg to evaluate any _PLD objects and you will see what I mean :).