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[gbinder] correct stability field wire format on Android 12 #133

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[gbinder] correct stability field wire format on Android 12 #133

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Commits on Oct 12, 2024

  1. [gbinder] correct stability field wire format on Android 12 

    On Android 12, the wire format of stability field is changed to also
include so-called "Binder wire format version", which starts at 1 [1].
A 32-bit-sized struct is re-interpreted into a 32-bit integer, with a
layout which makes it incompatible with the old version. Interestingly,
they reverted this idea in Android 13 [2], which makes the wire format
of the stability field the same as Android 11 again (as far as I know).

Add a new RPC protocol variant 'aidl4' to account for this difference.
Use this protocol on API level 31 through 32 and use 'aidl3' from API
level 33 onwards. The only difference from 'aidl3' is `finish_flatten_
binder()` function.

Interestingly, there is also a 16-bit-sized struct variant of the field
too [3]. However, to the best of my knowledge, this version is not used
in any of the released Android versions.

[1]: LineageOS/android_frameworks_native@89ddfc5
[2]: LineageOS/android_frameworks_native@16a4106
[3]: LineageOS/android_frameworks_native@14e4cfa
    @peat-psuwit
    peat-psuwit committed Oct 12, 2024
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  2. [gbinder] uses aidl3 servicemanager on API level 31 & 32 

    Nikita (@NotKit) noticed that the change in commit f227ae4
("[gbinder] All binder objects need stability field in Android 11.
JB#58951") has made the aidl4 servicemanager variant redundant. In fact,
using aidl4 variant will cause an extra stability field to be sent on
the wire (luckily it has not caused any problem).

I've tried using aidl3 variant on Volla Phone X23 which runs Halium 12
(API level 32), and service registration still work, which seems to
validate this theory. Thus, stop using aidl4 servicemanager variant on
any of the API level-based config, as it no longer correspond to any of
Android versions.

Note that this commit doesn't outright remove aidl4 variant, as doing so
would break configurations which explicitly request its use. This commit
doesn't doesn't alias the aidl4 variant to aidl3 variant either.
Manually requesting a certain variant could mean some unusual setup;
aliasing aidl4 to aidl3 could break such setup.
    @peat-psuwit
    peat-psuwit committed Oct 12, 2024
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