665770ec84
They were introduced back when std_detect was a standalone crate published to crates.io. The motivation for std_detect_dlsym_getauxval was to allow using getauxval without dlopen when statically linking musl, which we now unconditionally do for musl. And for std_detect_file_io to allow no_std usage, which std_detect now supports even with that feature enabled as it directly uses libc. This also prevents accidentally disabling runtime feature detection when using cargo build -Zbuild-std -Zbuild-std-features=
69 lines
2.9 KiB
Markdown
69 lines
2.9 KiB
Markdown
`std::detect` - Rust's standard library run-time CPU feature detection
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=======
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The private `std::detect` module implements run-time feature detection in Rust's
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standard library. This allows detecting whether the CPU the binary runs on
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supports certain features, like SIMD instructions.
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# Usage
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`std::detect` APIs are available as part of `libstd`. Prefer using it via the
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standard library than through this crate. Unstable features of `std::detect` are
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available on nightly Rust behind various feature-gates.
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If you need run-time feature detection in `#[no_std]` environments, Rust `core`
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library cannot help you. By design, Rust `core` is platform independent, but
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performing run-time feature detection requires a certain level of cooperation
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from the platform.
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You can then manually include `std_detect` as a dependency to get similar
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run-time feature detection support than the one offered by Rust's standard
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library. We intend to make `std_detect` more flexible and configurable in this
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regard to better serve the needs of `#[no_std]` targets.
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# Platform support
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* All `x86`/`x86_64` targets are supported on all platforms by querying the
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`cpuid` instruction directly for the features supported by the hardware and
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the operating system. `std_detect` assumes that the binary is an user-space
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application.
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* Linux/Android:
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* `arm{32, 64}`, `mips{32,64}{,el}`, `powerpc{32,64}{,le}`, `loongarch{32,64}`, `s390x`:
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`std_detect` supports these on Linux by querying ELF auxiliary vectors (using `getauxval`
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when available), and if that fails, by querying `/proc/self/auxv`.
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* `arm64`: partial support for doing run-time feature detection by directly
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querying `mrs` is implemented for Linux >= 4.11, but not enabled by default.
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* `riscv{32,64}`:
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`std_detect` supports these on Linux by querying `riscv_hwprobe`, and
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by querying ELF auxiliary vectors (using `getauxval` when available).
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* FreeBSD:
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* `arm32`, `powerpc64`: `std_detect` supports these on FreeBSD by querying ELF
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auxiliary vectors using `elf_aux_info`.
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* `arm64`: run-time feature detection is implemented by directly querying `mrs`.
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* OpenBSD:
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* `powerpc64`: `std_detect` supports these on OpenBSD by querying ELF auxiliary
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vectors using `elf_aux_info`.
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* `arm64`: run-time feature detection is implemented by querying `sysctl`.
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* Windows:
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* `arm64`: run-time feature detection is implemented by querying `IsProcessorFeaturePresent`.
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# License
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This project is licensed under either of
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* Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or
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http://www.apache.org/licenses/LICENSE-2.0)
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* MIT license ([LICENSE-MIT](LICENSE-MIT) or
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http://opensource.org/licenses/MIT)
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at your option.
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# Contribution
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Unless you explicitly state otherwise, any contribution intentionally submitted
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for inclusion in `std_detect` by you, as defined in the Apache-2.0 license,
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shall be dual licensed as above, without any additional terms or conditions.
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