Using `External`, table load order matters, but can't be controlled

[martin-hughes]

About 13 of the uACPI dumps fail to parse correctly because they rely on:

• SSDTs or DSDT using External to reference other SSDTs
• SSDTs not being loaded in the perfect order to guarantee Externals are defined in advance (instead, they're loaded in the order within the dump file)

I think I'm right in saying that there's no guarantee that SSDTs will be defined by the system in the perfect order? Also I don't know if Externals could form a loop where:

• SSDT1 defines Object A, uses External B in some method
• SSDT2 defines Object B, uses External A in some method

Below is an ASL script showing an example of this issue.

I guess the fix will be something along these lines?

• when parsing an External:
  • Create empty scopes if they haven't previously been encountered,
  • Create placeholder objects - probably a new, internal-only, Object/ObjectType,
• Return an error if a placeholder object is used as an argument in any operation.

Thoughts?

---

In this order, the tables can't be parsed - ParseFail(LevelDoesNotExist(AmlName([Root, Segment("_SB_"), Segment("SCP2")]))). Swap Table2 and Table3 and it can be parsed.

DefinitionBlock("", "SSDT", 1, "RSACPI", "Table2", 1) {
    External (_SB.SCP2.SCP3)

    Scope (_SB.SCP2.SCP3) {
        Name (NAM3, 0x03)
    }
}

DefinitionBlock("", "SSDT", 1, "RSACPI", "Table3", 1) {
    Scope (_SB) {
        Scope (SCP2) {
            Scope (SCP3) {
                Name (NAM2, 0x02)
            }
        }
    }
}

DefinitionBlock("", "DSDT", 1, "RSACPI", "Table1", 1) {
    Scope (_SB) {
        Scope (SCP1) {
            Name (NAM1, 0x01)
        }
    }
}

[martin-hughes]

Ah - I just realised that you need to pass the -f argument to iasl in order to compile that script. (I accidentally left that flag in from debugging something else) Nonetheless, it matches the structure of the ACPI dump I was looking at.

I'll see if I can come up with a better script.

[martin-hughes]

A new script showing the same failure, but not requiring force-compile. Once again, swap the tables to get parsing to work.

DefinitionBlock("", "SSDT", 1, "RSACPI", "Table2", 1) {
    External (_SB_.SCP2.SCP3, DeviceObj)

    Scope (_SB.SCP2.SCP3) {
        Name (NAM3, 0x03)
    }
}

DefinitionBlock("", "SSDT", 1, "RSACPI", "Table3", 1) {
    Scope (_SB) {
        Device (SCP2) {
            Name (_HID, 0x01)
            Device (SCP3) {
                Name (_HID, 0x01)
                Name (NAM2, 0x02)
            }
        }
    }
}