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std_detect: Always avoid dlsym on *-linux-gnu* targets (#1375)

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Taiki Endo 2023-02-04 03:23:09 +09:00 • committed by GitHub
parent a36f5bd7c8
commit 1829ee06f0
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2 changed files with 19 additions and 3 deletions
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2
library/stdarch/crates/std_detect/README.md
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@ -30,6 +30,8 @@ run-time feature detection. When this feature is disabled, `std_detect` assumes
that [`getauxval`] is linked to the binary. If that is not the case the behavior
is undefined.
Note: This feature is ignored on `*-linux-gnu*` targets, since all `*-linux-gnu*` targets ([since Rust 1.64](https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html)) have glibc requirements higher than [glibc 2.16 that added `getauxval`](https://sourceware.org/legacy-ml/libc-announce/2012/msg00000.html), and we can safely assume [`getauxval`] is linked to the binary.
* `std_detect_file_io` (enabled by default, requires `std`): Enable to perform run-time feature
detection using file APIs (e.g. `/proc/cpuinfo`, etc.) if other more performant
methods fail. This feature requires `libstd` as a dependency, preventing the

20
library/stdarch/crates/std_detect/src/detect/os/linux/auxvec.rs
View file

@ -54,13 +54,21 @@ pub(crate) struct AuxVec {
/// error, cpuinfo still can (and will) be used to try to perform run-time
/// feature detecton on some platforms.
///
/// Note: The `std_detect_dlsym_getauxval` cargo feature is ignored on `*-linux-gnu*` targets,
/// since [all `*-linux-gnu*` targets ([since Rust 1.64](https://blog.rust-lang.org/2022/08/01/Increasing-glibc-kernel-requirements.html))
/// have glibc requirements higher than [glibc 2.16 that added `getauxval`](https://sourceware.org/legacy-ml/libc-announce/2012/msg00000.html),
/// and we can safely assume [`getauxval`] is linked to the binary.
///
/// For more information about when `getauxval` is available check the great
/// [`auxv` crate documentation][auxv_docs].
///
/// [auxvec_h]: https://github.com/torvalds/linux/blob/master/include/uapi/linux/auxvec.h
/// [auxv_docs]: https://docs.rs/auxv/0.3.3/auxv/
pub(crate) fn auxv() -> Result<AuxVec, ()> {
#[cfg(feature = "std_detect_dlsym_getauxval")]
#[cfg(all(
feature = "std_detect_dlsym_getauxval",
not(all(target_os = "linux", target_env = "gnu"))
))]
{
// Try to call a dynamically-linked getauxval function.
if let Ok(hwcap) = getauxval(AT_HWCAP) {
@ -101,7 +109,10 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
}
}
#[cfg(not(feature = "std_detect_dlsym_getauxval"))]
#[cfg(any(
not(feature = "std_detect_dlsym_getauxval"),
all(target_os = "linux", target_env = "gnu")
))]
{
// Targets with only AT_HWCAP:
#[cfg(any(
@ -154,7 +165,10 @@ pub(crate) fn auxv() -> Result<AuxVec, ()> {
/// Tries to read the `key` from the auxiliary vector by calling the
/// dynamically-linked `getauxval` function. If the function is not linked,
/// this function return `Err`.
#[cfg(feature = "std_detect_dlsym_getauxval")]
#[cfg(all(
feature = "std_detect_dlsym_getauxval",
not(all(target_os = "linux", target_env = "gnu"))
))]
fn getauxval(key: usize) -> Result<usize, ()> {
use libc;
pub type F = unsafe extern "C" fn(usize) -> usize;