如何在acpiexec提示符下向ACPI控制方法传递buffer参数？

问题场景 #

定义了Buffer对象BUF0和用于遍历它的ACPI方法IDXA，ASL代码如下：

DefinitionBlock ("dsdt.asl", "DSDT", 0x02, "", "", 0x0) 
{ 
    Name (BUF0, Buffer() {1, 2, 3, 4, 5, 6, 7, 8, 9, 10})

    Method (IDXA, 1) 
    {
        local0 = sizeof(Arg0) 
        local1 = 0 // use this as the index value 
        printf ("The size of the buffer is %o, Arg0 is: %o", local0, Arg0) 
        while (local0 > local1) 
        {
            printf ("inside loop:")
            printf ("%o", DeRefOf(Arg0[local1]))
            local1++ 
        }
    }
} 

编译与运行步骤 #

• 编译代码：

  iasl dsdt.asl
  

• 运行编译后的AML文件：

  acpiexec dsdt.aml
  

错误现象 #

在acpiexec提示符下尝试直接传递\BUF0调用\IDXA：

- eval \IDXA \BUF0  

得到错误输出：

Evaluating \IDXA
ACPI Debug:  "The size of the buffer is 0000000000000008, Arg0 is: 0000000000000000"
ACPI Debug:  "inside loop:"
ACPI Error: Needed [Buffer/String/Package], found [Integer] 0x555d39f95770 (20190509/exresop-617)
ACPI Error: AE_AML_OPERAND_TYPE, While resolving operands for [Index] (20190509/dswexec-500)
Failed at AML Offset 00056, Opcode 0088: Index (Arg0, Local1)

Initialized Local Variables for Method [IDXA]:
    Local0: 0x555d39f95840 <Obj>             Integer 0000000000000008
    Local1: 0x555d39f956f0 <Obj>             Integer 0000000000000000

Initialized Arguments for Method [IDXA]:  (1 arguments defined for method invocation)
    Arg0:   0x555d39f95770 <Obj>             Integer 0000000000000000

ACPI Error: Aborting method \IDXA due to previous error (AE_AML_OPERAND_TYPE) (20190509/psparse-581)
ACPI Error: AE_AML_OPERAND_TYPE, while executing \IDXA from AML Debugger (20190509/dbexec-226)
Evaluation of \IDXA failed with status AE_AML_OPERAND_TYPE

错误显示Arg0被识别为整数而非Buffer，导致索引操作失败。但单独访问\BUF0是正常的：

- eval \BUF0
Evaluating \BUF0
Evaluation of \BUF0 returned object 0x55b97b465cd0, external buffer length 28
  [Buffer] Length 0A =     0000: 01 02 03 04 05 06 07 00 00 08                    // ..........

解决方法 #

1. 正确的acpiexec调用命令 #

acpiexec中直接传递对象路径时，不会传递对象本身，而是返回无效整数。需要使用^前缀表示名称引用，将Buffer对象的引用传递给方法：

eval \IDXA ^\BUF0

2. 修正ASL方法中的逻辑错误 #

原方法中sizeof(Arg0)获取的是引用对象的字节大小（64位系统下为8），而非Buffer的实际长度。需要替换为SizeOfBuffer(DeRefOf(Arg0))来获取Buffer的真实长度，同时调整索引操作的写法：

Method (IDXA, 1) 
{
    local0 = SizeOfBuffer(DeRefOf(Arg0)) 
    local1 = 0 // use this as the index value 
    printf ("The size of the buffer is %o", local0) 
    while (local0 > local1) 
    {
        printf ("inside loop: ")
        printf ("%o", DeRefOf(Arg0)[local1])
        local1++ 
    }
}

原理说明 #

• ^前缀告诉acpiexec传递的是对象的名称引用，而非尝试解析对象的值，这样Arg0会被正确识别为Buffer类型的引用。
• DeRefOf()用于解引用获取到Buffer对象本身，SizeOfBuffer()则专门用于获取Buffer的字节长度，替代原有的sizeof()函数（后者对引用类型返回的是引用的大小）。

内容的提问来源于stack exchange，提问作者smwikipedia