std_detect: Always avoid dlsym on *-linux-gnu* targets #1375
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Since Rust 1.64, all `*-linux-gnu*` targets have glibc requirements higher than glibc 2.16 that `getauxval` added. Refs: - https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html - https://sourceware.org/legacy-ml/libc-announce/2012/msg00000.html
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lu-zero
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67: detect: Avoid dlsym on aarch64 linux-gnu r=taiki-e a=taiki-e As of nightly-2023-01-23, is_aarch64_feature_detected always uses dlsym by default on aarch64 linux, but on linux-gnu [aarch64 support is available on glibc 2.17+](https://sourceware.org/legacy-ml/libc-announce/2012/msg00001.html) and is newer than [glibc 2.16 that getauxval was added](https://sourceware.org/legacy-ml/libc-announce/2012/msg00000.html), so we can safely assume getauxval is linked to the binary. A patch on stdarch side: rust-lang/stdarch#1375 On other linux targets, we cannot assume that getauxval is always available yet (see stdarch PR linked above for details), so we continue to use is_aarch64_feature_detected which uses dlsym (+io fallback) instead of this module. Co-authored-by: Taiki Endo <te316e89@gmail.com>
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67: detect: Avoid dlsym on aarch64 linux-gnu r=taiki-e a=taiki-e As of nightly-2023-01-23, is_aarch64_feature_detected always uses dlsym by default on aarch64 linux, but on linux-gnu [aarch64 support is available on glibc 2.17+](https://sourceware.org/legacy-ml/libc-announce/2012/msg00001.html) and is newer than [glibc 2.16 that getauxval was added](https://sourceware.org/legacy-ml/libc-announce/2012/msg00000.html), so we can safely assume getauxval is linked to the binary. A patch on stdarch side: rust-lang/stdarch#1375 On other linux targets, we cannot assume that getauxval is always available yet (see stdarch PR linked above for details), so we continue to use is_aarch64_feature_detected which uses dlsym (+io fallback) instead of this module. Co-authored-by: Taiki Endo <te316e89@gmail.com>
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Co-authored-by: Amanieu d'Antras <amanieu@gmail.com>
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Currently, we use
dlsymon non-x861 Linux/Android when thestd_detect_dlsym_getauxvalfeature (enabled by default) is enabled becausegetauxvalmay not be available.However, since Rust 1.64, all
*-linux-gnu*targets have glibc requirements higher than glibc 2.16 thatgetauxvaladded, and we can safely assumegetauxvalis linked to the binary.Related #655 (fyi @briansmith)
IIUC, at this time, we can do this on only
*-linux-gnu*targets, because:*-linux-musl*, it seems thatgetauxvalis not always available, independent of version requirements: Undefined reference togetauxvalin functioninit_have_lse_atomicswhen compiling to nightlyaarch64-unknown-linux-muslrust#89626getauxvalis used on the C/C++ side).*-android*, according to auxv crate,getauxvalis available for android 4.3 or later, but the Android API requirement for Rust is still 4.0 (Ice Cream Sandwich).getauxvalis always available.*-linux-*targets (e.g.*-linux-uclibc*), according to auxv crate,getauxvalis not available.Footnotes
On x86, we use cpuid instead of auxv. ↩