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    //! Run-time feature detection for ARM on Linux.

    use arch::detect::Feature;
    use arch::detect::cache;
    use arch::detect::bit;
    use super::auxvec;
    use super::cpuinfo;

    /// Performs run-time feature detection.
    #[inline]
    pub fn check_for(x: Feature) -> bool {
        cache::test(x as u32, detect_features)
    }

    /// Try to read the features from the auxiliary vector, and if that fails, try
    /// to read them from /proc/cpuinfo.
    fn detect_features() -> cache::Initializer {
        let mut value = cache::Initializer::default();
        let enable_feature = |value: &mut cache::Initializer, f, enable| {
            if enable {
                value.set(f as u32);
            }
        };

        // The values are part of the platform-specific [asm/hwcap.h][hwcap]
        //
        // [hwcap]: https://github.com/torvalds/linux/blob/master/arch/arm64/include/uapi/asm/hwcap.h
        if let Ok(auxv) = auxvec::auxv() {
            enable_feature(&mut value, Feature::neon, bit::test(auxv.hwcap, 12));
            enable_feature(&mut value, Feature::pmull, bit::test(auxv.hwcap2, 1));
            return value;
        }

        if let Ok(c) = cpuinfo::CpuInfo::new() {
            enable_feature(&mut value, Feature::neon, c.field("Features").has("neon") &&
                !has_broken_neon(&c));
            enable_feature(&mut value, Feature::pmull, c.field("Features").has("pmull"));
            return value;
        }
        value
    }

    /// Is the CPU known to have a broken NEON unit?
    ///
    /// See https://crbug.com/341598.
    fn has_broken_neon(cpuinfo: &cpuinfo::CpuInfo) -> bool {
        cpuinfo.field("CPU implementer") == "0x51"
            && cpuinfo.field("CPU architecture") == "7"
            && cpuinfo.field("CPU variant") == "0x1"
            && cpuinfo.field("CPU part") == "0x04d"
            && cpuinfo.field("CPU revision") == "0"
    }

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