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李通洲
31 lines
1.8 KiB
C
31 lines
1.8 KiB
C
#pragma once
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// AIDL gives every method of an interface a transaction code at build time:
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//
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// static final int TRANSACTION_<method> = IBinder.FIRST_CALL_TRANSACTION + <declaration index>;
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//
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// so the number is a property of the `.aidl` of the release that built the device's jar, not of any
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// public header. Counting the methods in an AOSP checkout only describes that checkout, and it goes
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// wrong the moment a release or a vendor fork inserts a method ahead of the one being looked for:
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// `IWifiManager.getConnectionInfo` is 29 on Android 11 and 41 on Android 16. There is no negotiation
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// and no discovery -- a wrong code reaches a different method, or none.
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//
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// Being a compile-time constant, the value lands in the `static_values` array of the `X$Stub` class
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// in the jar's dex, paired position by position with that class's static field list. Reading the two
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// together gives the mapping of the build that is actually on the device, on any release, with
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// nothing to keep in sync.
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//
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// `libdexfile.so` cannot do this for us. It is dlopen-able from an app UID through the ART apex, but
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// it is not in the NDK and its only C ABI -- the `ADexFile_*` family -- covers methods, not fields;
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// the field and class-data APIs are C++ with no ABI guarantee.
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//
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// `ffReadFileBuffer` would work but pulls the whole jar through the heap for one integer. The jar is
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// mapped instead, and only the pages actually read are faulted in.
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#include "fastfetch.h"
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// Resolves the int value of `<classDescriptor>.<fieldName>` out of the `classes.dex` of `jarPath`.
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// `classDescriptor` is the dex type descriptor, e.g. "Landroid/net/wifi/IWifiManager$Stub;".
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// Returns nullptr on success, a static message otherwise.
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[[gnu::nonnull(1, 2, 3, 4), nodiscard]] const char* ffDexStaticInt(const char* jarPath, const char* classDescriptor, const char* fieldName, int32_t* result);
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