| //! Android ABI-compatibility module |
| //! |
| //! The ABI of Android has changed quite a bit over time, and libstd attempts to |
| //! be both forwards and backwards compatible as much as possible. We want to |
| //! always work with the most recent version of Android, but we also want to |
| //! work with older versions of Android for whenever projects need to. |
| //! |
| //! Our current minimum supported Android version is `android-9`, e.g., Android |
| //! with API level 9. We then in theory want to work on that and all future |
| //! versions of Android! |
| //! |
| //! Some of the detection here is done at runtime via `dlopen` and |
| //! introspection. Other times no detection is performed at all and we just |
| //! provide a fallback implementation as some versions of Android we support |
| //! don't have the function. |
| //! |
| //! You'll find more details below about why each compatibility shim is needed. |
| |
| #![cfg(target_os = "android")] |
| |
| use libc::{c_int, sighandler_t}; |
| |
| use super::weak::weak; |
| |
| // The `log2` and `log2f` functions apparently appeared in android-18, or at |
| // least you can see they're not present in the android-17 header [1] and they |
| // are present in android-18 [2]. |
| // |
| // [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms |
| // /android-17/arch-arm/usr/include/math.h |
| // [2]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms |
| // /android-18/arch-arm/usr/include/math.h |
| // |
| // Note that these shims are likely less precise than directly calling `log2`, |
| // but hopefully that should be enough for now... |
| // |
| // Note that mathematically, for any arbitrary `y`: |
| // |
| // log_2(x) = log_y(x) / log_y(2) |
| // = log_y(x) / (1 / log_2(y)) |
| // = log_y(x) * log_2(y) |
| // |
| // Hence because `ln` (log_e) is available on all Android we just choose `y = e` |
| // and get: |
| // |
| // log_2(x) = ln(x) * log_2(e) |
| |
| #[cfg(not(test))] |
| pub fn log2f32(f: f32) -> f32 { |
| f.ln() * crate::f32::consts::LOG2_E |
| } |
| |
| #[cfg(not(test))] |
| pub fn log2f64(f: f64) -> f64 { |
| f.ln() * crate::f64::consts::LOG2_E |
| } |
| |
| // Back in the day [1] the `signal` function was just an inline wrapper |
| // around `bsd_signal`, but starting in API level android-20 the `signal` |
| // symbols was introduced [2]. Finally, in android-21 the API `bsd_signal` was |
| // removed [3]. |
| // |
| // Basically this means that if we want to be binary compatible with multiple |
| // Android releases (oldest being 9 and newest being 21) then we need to check |
| // for both symbols and not actually link against either. |
| // |
| // [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms |
| // /android-18/arch-arm/usr/include/signal.h |
| // [2]: https://chromium.googlesource.com/android_tools/+/fbd420/ndk_experimental |
| // /platforms/android-20/arch-arm |
| // /usr/include/signal.h |
| // [3]: https://chromium.googlesource.com/android_tools/+/20ee6d/ndk/platforms |
| // /android-21/arch-arm/usr/include/signal.h |
| pub unsafe fn signal(signum: c_int, handler: sighandler_t) -> sighandler_t { |
| weak!(fn signal(c_int, sighandler_t) -> sighandler_t); |
| weak!(fn bsd_signal(c_int, sighandler_t) -> sighandler_t); |
| |
| let f = signal.get().or_else(|| bsd_signal.get()); |
| let f = f.expect("neither `signal` nor `bsd_signal` symbols found"); |
| f(signum, handler) |
| } |
