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Wrong ffi_type for unsigned numbers causes bugs on some platforms

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#1,435 3 comments 2 reactions 0 assignees View on GitHub

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
android, c, java
Domain
devtools, mobile-dev

Research direction

Start with the minimal reproducible example linked in the report, focusing on JNA's IntegerType and the UINT16 argument passed to the native hello function. Reproduce the difference between optimized and unoptimized Android builds, then trace the unsigned-short FFI representation; done means hello returns true with the expected value on the affected architectures.

Written by the indexing model from the issue text.

Description

Provide complete information about the problem
  1. Version of JNA and related jars
    5.11.0@aar
  2. Version and vendor of the java virtual machine
    ART @ Android 11
  3. Operating system
    Android 11
  4. System architecture (CPU type, bitness of the JVM)
    arm64-v8a, x86_64, possibly more
    Output of clang --version:
    Compiler Android (7019983 based on r365631c3) clang version 9.0.9 (https://android.googlesource.com/toolchain/llvm-project a2a1e703c0edb03ba29944e529ccbf457742737b) (based on LLVM 9.0.9svn).
  5. Complete description of the problem
    Function argument of type unsigned short passed by JNA to native code does not behave correctly when the code is compiled with optimizations enabled. The is caused by the fact that LLVM is counting on the argument being stored in straight format (as it should be) instead of two's complement.
  6. Steps to reproduce
    Minimal reproducible example available here.
    The hello function in the following code should return true, but returns false.
const unsigned short CONSTANT = 0x8810u;

bool hello(unsigned short argument) {
    __android_log_print(ANDROID_LOG_WARN, TAG, "argument value as %%#010x=%#010x %%d=%d, as %%u=%u, as %%hu=%hu", argument, argument, argument, argument);
    __android_log_print(ANDROID_LOG_WARN, TAG, "CONSTANT value as %%#010x=%#010x %%d=%d, as %%u=%u, as %%hu=%hu", CONSTANT, CONSTANT, CONSTANT, CONSTANT);
    switch (argument) {
        case CONSTANT:
            return true;
        default:
            return false;
    }
}

    private void logValueFromJna() {
        boolean on = lib.hello(new UINT16(0x8810));
        Log.w("JNA-BUG", "hello returned correct value? " + on);
    }

    public static class UINT16 extends IntegerType {

        @SuppressWarnings("unused")
        public UINT16() {
            this(0);
        }

        public UINT16(int value) {
            super(2, value, true);
        }
    }

    interface TestLibrary extends Library {
        boolean hello(UINT16 argument);
    }

Log output with optimizations disabled:

W/JNA-BUG-NATIVE: argument value as %#010x=0x00008810 %d=34832, as %u=34832, as %hu=34832
W/JNA-BUG-NATIVE: CONSTANT value as %#010x=0x00008810 %d=34832, as %u=34832, as %hu=34832
W/JNA-BUG: hello returned correct value? true

Log output with optimizations enabled:

W/JNA-BUG-NATIVE: argument value as %#010x=0xffff8810 %d=-30704, as %u=4294936592, as %hu=34832
W/JNA-BUG-NATIVE: CONSTANT value as %#010x=0x00008810 %d=34832, as %u=34832, as %hu=34832
W/JNA-BUG: hello returned correct value? false
Dominant language
Java
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Avg merge
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Merged PRs (30d)
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