5ff6ac4287
This makes a few changes to the weak symbol macros in `sys::unix`:
- `dlsym!` is added to keep the functionality for runtime `dlsym`
lookups, like for `__pthread_get_minstack@GLIBC_PRIVATE` that we don't
want to show up in ELF symbol tables.
- `weak!` now uses `#[linkage = "extern_weak"]` symbols, so its runtime
behavior is just a simple null check. This is also used by `syscall!`.
- On non-ELF targets (macos/ios) where that linkage is not known to
behave, `weak!` is just an alias to `dlsym!` for the old behavior.
- `raw_syscall!` is added to always call `libc::syscall` on linux and
android, for cases like `clone3` that have no known libc wrapper.
The new `weak!` linkage does mean that you'll get versioned symbols if
you build with a newer glibc, like `WEAK DEFAULT UND statx@GLIBC_2.28`.
This might seem problematic, but old non-weak symbols can tie the build
to new versions too, like `dlsym@GLIBC_2.34` from their recent library
unification. If you build with an old glibc like `dist-x86_64-linux`
does, you'll still get unversioned `WEAK DEFAULT UND statx`, which may
be resolved based on the runtime glibc.
I also found a few functions that don't need to be weak anymore:
- Android can directly use `ftruncate64`, `pread64`, and `pwrite64`, as
these were added in API 12, and our baseline is API 14.
- Linux can directly use `splice`, added way back in glibc 2.5 and
similarly old musl. Android only added it in API 21 though.
82 lines
3.4 KiB
Rust
82 lines
3.4 KiB
Rust
//! Android ABI-compatibility module
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//!
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//! The ABI of Android has changed quite a bit over time, and libstd attempts to
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//! be both forwards and backwards compatible as much as possible. We want to
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//! always work with the most recent version of Android, but we also want to
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//! work with older versions of Android for whenever projects need to.
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//!
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//! Our current minimum supported Android version is `android-9`, e.g., Android
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//! with API level 9. We then in theory want to work on that and all future
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//! versions of Android!
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//!
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//! Some of the detection here is done at runtime via `dlopen` and
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//! introspection. Other times no detection is performed at all and we just
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//! provide a fallback implementation as some versions of Android we support
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//! don't have the function.
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//!
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//! You'll find more details below about why each compatibility shim is needed.
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#![cfg(target_os = "android")]
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use libc::{c_int, sighandler_t};
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use super::weak::weak;
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// The `log2` and `log2f` functions apparently appeared in android-18, or at
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// least you can see they're not present in the android-17 header [1] and they
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// are present in android-18 [2].
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//
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// [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms
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// /android-17/arch-arm/usr/include/math.h
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// [2]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms
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// /android-18/arch-arm/usr/include/math.h
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//
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// Note that these shims are likely less precise than directly calling `log2`,
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// but hopefully that should be enough for now...
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//
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// Note that mathematically, for any arbitrary `y`:
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//
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// log_2(x) = log_y(x) / log_y(2)
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// = log_y(x) / (1 / log_2(y))
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// = log_y(x) * log_2(y)
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//
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// Hence because `ln` (log_e) is available on all Android we just choose `y = e`
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// and get:
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//
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// log_2(x) = ln(x) * log_2(e)
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#[cfg(not(test))]
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pub fn log2f32(f: f32) -> f32 {
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f.ln() * crate::f32::consts::LOG2_E
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}
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#[cfg(not(test))]
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pub fn log2f64(f: f64) -> f64 {
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f.ln() * crate::f64::consts::LOG2_E
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}
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// Back in the day [1] the `signal` function was just an inline wrapper
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// around `bsd_signal`, but starting in API level android-20 the `signal`
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// symbols was introduced [2]. Finally, in android-21 the API `bsd_signal` was
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// removed [3].
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//
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// Basically this means that if we want to be binary compatible with multiple
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// Android releases (oldest being 9 and newest being 21) then we need to check
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// for both symbols and not actually link against either.
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//
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// [1]: https://chromium.googlesource.com/android_tools/+/20ee6d20/ndk/platforms
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// /android-18/arch-arm/usr/include/signal.h
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// [2]: https://chromium.googlesource.com/android_tools/+/fbd420/ndk_experimental
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// /platforms/android-20/arch-arm
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// /usr/include/signal.h
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// [3]: https://chromium.googlesource.com/android_tools/+/20ee6d/ndk/platforms
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// /android-21/arch-arm/usr/include/signal.h
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pub unsafe fn signal(signum: c_int, handler: sighandler_t) -> sighandler_t {
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weak!(fn signal(c_int, sighandler_t) -> sighandler_t);
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weak!(fn bsd_signal(c_int, sighandler_t) -> sighandler_t);
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let f = signal.get().or_else(|| bsd_signal.get());
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let f = f.expect("neither `signal` nor `bsd_signal` symbols found");
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f(signum, handler)
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}
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