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Diffstat (limited to 'library/std_detect/src/detect/os/linux/auxvec.rs')
| -rw-r--r-- | library/std_detect/src/detect/os/linux/auxvec.rs | 341 |
1 files changed, 341 insertions, 0 deletions
diff --git a/library/std_detect/src/detect/os/linux/auxvec.rs b/library/std_detect/src/detect/os/linux/auxvec.rs new file mode 100644 index 00000000000..54f52aa7533 --- /dev/null +++ b/library/std_detect/src/detect/os/linux/auxvec.rs @@ -0,0 +1,341 @@ +//! Parses ELF auxiliary vectors. +#![allow(dead_code)] + +pub(crate) const AT_NULL: usize = 0; + +/// Key to access the CPU Hardware capabilities bitfield. +pub(crate) const AT_HWCAP: usize = 16; +/// Key to access the CPU Hardware capabilities 2 bitfield. +#[cfg(any( + target_arch = "aarch64", + target_arch = "arm", + target_arch = "powerpc", + target_arch = "powerpc64", + target_arch = "s390x", +))] +pub(crate) const AT_HWCAP2: usize = 26; + +/// Cache HWCAP bitfields of the ELF Auxiliary Vector. +/// +/// If an entry cannot be read all the bits in the bitfield are set to zero. +/// This should be interpreted as all the features being disabled. +#[derive(Debug, Copy, Clone)] +#[cfg_attr(test, derive(PartialEq))] +pub(crate) struct AuxVec { + pub hwcap: usize, + #[cfg(any( + target_arch = "aarch64", + target_arch = "arm", + target_arch = "powerpc", + target_arch = "powerpc64", + target_arch = "s390x", + ))] + pub hwcap2: usize, +} + +/// ELF Auxiliary Vector +/// +/// The auxiliary vector is a memory region in a running ELF program's stack +/// composed of (key: usize, value: usize) pairs. +/// +/// The keys used in the aux vector are platform dependent. For Linux, they are +/// defined in [linux/auxvec.h][auxvec_h]. The hardware capabilities of a given +/// CPU can be queried with the `AT_HWCAP` and `AT_HWCAP2` keys. +/// +/// There is no perfect way of reading the auxiliary vector. +/// +/// - If the `std_detect_dlsym_getauxval` cargo feature is enabled, this will use +/// `getauxval` if its linked to the binary, and otherwise proceed to a fallback implementation. +/// When `std_detect_dlsym_getauxval` is disabled, this will assume that `getauxval` is +/// linked to the binary - if that is not the case the behavior is undefined. +/// - Otherwise, if the `std_detect_file_io` cargo feature is enabled, it will +/// try to read `/proc/self/auxv`. +/// - If that fails, this function returns an error. +/// +/// Note that run-time feature detection is not invoked for features that can +/// be detected at compile-time. +/// +/// Note: The `std_detect_dlsym_getauxval` cargo feature is ignored on +/// `*-linux-{gnu,musl,ohos}*` and `*-android*` targets because we can safely assume `getauxval` +/// is linked to the binary. +/// - `*-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). +/// - `*-linux-musl*` targets ([at least since Rust 1.15](https://github.com/rust-lang/rust/blob/1.15.0/src/ci/docker/x86_64-musl/build-musl.sh#L15)) +/// use musl newer than [musl 1.1.0 that added `getauxval`](https://git.musl-libc.org/cgit/musl/tree/WHATSNEW?h=v1.1.0#n1197) +/// - `*-linux-ohos*` targets use a [fork of musl 1.2](https://gitee.com/openharmony/docs/blob/master/en/application-dev/reference/native-lib/musl.md) +/// - `*-android*` targets ([since Rust 1.68](https://blog.rust-lang.org/2023/01/09/android-ndk-update-r25.html)) +/// have the minimum supported API level higher than [Android 4.3 (API level 18) that added `getauxval`](https://github.com/aosp-mirror/platform_bionic/blob/d3ebc2f7c49a9893b114124d4a6b315f3a328764/libc/include/sys/auxv.h#L49). +/// +/// 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, ()> { + // Try to call a getauxval function. + if let Ok(hwcap) = getauxval(AT_HWCAP) { + // Targets with only AT_HWCAP: + #[cfg(any( + target_arch = "riscv32", + target_arch = "riscv64", + target_arch = "mips", + target_arch = "mips64", + target_arch = "loongarch32", + target_arch = "loongarch64", + ))] + { + // Zero could indicate that no features were detected, but it's also used to indicate + // an error. In either case, try the fallback. + if hwcap != 0 { + return Ok(AuxVec { hwcap }); + } + } + + // Targets with AT_HWCAP and AT_HWCAP2: + #[cfg(any( + target_arch = "aarch64", + target_arch = "arm", + target_arch = "powerpc", + target_arch = "powerpc64", + target_arch = "s390x", + ))] + { + if let Ok(hwcap2) = getauxval(AT_HWCAP2) { + // Zero could indicate that no features were detected, but it's also used to indicate + // an error. In particular, on many platforms AT_HWCAP2 will be legitimately zero, + // since it contains the most recent feature flags. Use the fallback only if no + // features were detected at all. + if hwcap != 0 || hwcap2 != 0 { + return Ok(AuxVec { hwcap, hwcap2 }); + } + } + } + + // Intentionnaly not used + let _ = hwcap; + } + + #[cfg(feature = "std_detect_file_io")] + { + // If calling getauxval fails, try to read the auxiliary vector from + // its file: + auxv_from_file("/proc/self/auxv") + } + #[cfg(not(feature = "std_detect_file_io"))] + { + Err(()) + } +} + +/// Tries to read the `key` from the auxiliary vector by calling the +/// `getauxval` function. If the function is not linked, this function return `Err`. +fn getauxval(key: usize) -> Result<usize, ()> { + type F = unsafe extern "C" fn(libc::c_ulong) -> libc::c_ulong; + cfg_if::cfg_if! { + if #[cfg(all( + feature = "std_detect_dlsym_getauxval", + not(all( + target_os = "linux", + any(target_env = "gnu", target_env = "musl", target_env = "ohos"), + )), + not(target_os = "android"), + ))] { + let ffi_getauxval: F = unsafe { + let ptr = libc::dlsym(libc::RTLD_DEFAULT, c"getauxval".as_ptr()); + if ptr.is_null() { + return Err(()); + } + core::mem::transmute(ptr) + }; + } else { + let ffi_getauxval: F = libc::getauxval; + } + } + Ok(unsafe { ffi_getauxval(key as libc::c_ulong) as usize }) +} + +/// Tries to read the auxiliary vector from the `file`. If this fails, this +/// function returns `Err`. +#[cfg(feature = "std_detect_file_io")] +pub(super) fn auxv_from_file(file: &str) -> Result<AuxVec, ()> { + let file = super::read_file(file)?; + + // See <https://github.com/torvalds/linux/blob/v5.15/include/uapi/linux/auxvec.h>. + // + // The auxiliary vector contains at most 34 (key,value) fields: from + // `AT_MINSIGSTKSZ` to `AT_NULL`, but its number may increase. + let len = file.len(); + let mut buf = alloc::vec![0_usize; 1 + len / core::mem::size_of::<usize>()]; + unsafe { + core::ptr::copy_nonoverlapping(file.as_ptr(), buf.as_mut_ptr() as *mut u8, len); + } + + auxv_from_buf(&buf) +} + +/// Tries to interpret the `buffer` as an auxiliary vector. If that fails, this +/// function returns `Err`. +#[cfg(feature = "std_detect_file_io")] +fn auxv_from_buf(buf: &[usize]) -> Result<AuxVec, ()> { + // Targets with only AT_HWCAP: + #[cfg(any( + target_arch = "riscv32", + target_arch = "riscv64", + target_arch = "mips", + target_arch = "mips64", + target_arch = "loongarch32", + target_arch = "loongarch64", + ))] + { + for el in buf.chunks(2) { + match el[0] { + AT_NULL => break, + AT_HWCAP => return Ok(AuxVec { hwcap: el[1] }), + _ => (), + } + } + } + // Targets with AT_HWCAP and AT_HWCAP2: + #[cfg(any( + target_arch = "aarch64", + target_arch = "arm", + target_arch = "powerpc", + target_arch = "powerpc64", + target_arch = "s390x", + ))] + { + let mut hwcap = None; + // For some platforms, AT_HWCAP2 was added recently, so let it default to zero. + let mut hwcap2 = 0; + for el in buf.chunks(2) { + match el[0] { + AT_NULL => break, + AT_HWCAP => hwcap = Some(el[1]), + AT_HWCAP2 => hwcap2 = el[1], + _ => (), + } + } + + if let Some(hwcap) = hwcap { + return Ok(AuxVec { hwcap, hwcap2 }); + } + } + // Suppress unused variable + let _ = buf; + Err(()) +} + +#[cfg(test)] +mod tests { + use super::*; + + // FIXME: on mips/mips64 getauxval returns 0, and /proc/self/auxv + // does not always contain the AT_HWCAP key under qemu. + #[cfg(any( + target_arch = "arm", + target_arch = "powerpc", + target_arch = "powerpc64", + target_arch = "s390x", + ))] + #[test] + fn auxv_crate() { + let v = auxv(); + if let Ok(hwcap) = getauxval(AT_HWCAP) { + let rt_hwcap = v.expect("failed to find hwcap key").hwcap; + assert_eq!(rt_hwcap, hwcap); + } + + // Targets with AT_HWCAP and AT_HWCAP2: + #[cfg(any( + target_arch = "aarch64", + target_arch = "arm", + target_arch = "powerpc", + target_arch = "powerpc64", + target_arch = "s390x", + ))] + { + if let Ok(hwcap2) = getauxval(AT_HWCAP2) { + let rt_hwcap2 = v.expect("failed to find hwcap2 key").hwcap2; + assert_eq!(rt_hwcap2, hwcap2); + } + } + } + + #[test] + fn auxv_dump() { + if let Ok(auxvec) = auxv() { + println!("{:?}", auxvec); + } else { + println!("both getauxval() and reading /proc/self/auxv failed!"); + } + } + + #[cfg(feature = "std_detect_file_io")] + cfg_if::cfg_if! { + if #[cfg(target_arch = "arm")] { + #[test] + fn linux_rpi3() { + let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-rpi3.auxv"); + println!("file: {file}"); + let v = auxv_from_file(file).unwrap(); + assert_eq!(v.hwcap, 4174038); + assert_eq!(v.hwcap2, 16); + } + + #[test] + fn linux_macos_vb() { + let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/macos-virtualbox-linux-x86-4850HQ.auxv"); + println!("file: {file}"); + // The file contains HWCAP but not HWCAP2. In that case, we treat HWCAP2 as zero. + let v = auxv_from_file(file).unwrap(); + assert_eq!(v.hwcap, 126614527); + assert_eq!(v.hwcap2, 0); + } + } else if #[cfg(target_arch = "aarch64")] { + #[cfg(target_endian = "little")] + #[test] + fn linux_artificial_aarch64() { + let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-artificial-aarch64.auxv"); + println!("file: {file}"); + let v = auxv_from_file(file).unwrap(); + assert_eq!(v.hwcap, 0x0123456789abcdef); + assert_eq!(v.hwcap2, 0x02468ace13579bdf); + } + #[cfg(target_endian = "little")] + #[test] + fn linux_no_hwcap2_aarch64() { + let file = concat!(env!("CARGO_MANIFEST_DIR"), "/src/detect/test_data/linux-no-hwcap2-aarch64.auxv"); + println!("file: {file}"); + let v = auxv_from_file(file).unwrap(); + // An absent HWCAP2 is treated as zero, and does not prevent acceptance of HWCAP. + assert_ne!(v.hwcap, 0); + assert_eq!(v.hwcap2, 0); + } + } + } + + #[test] + #[cfg(feature = "std_detect_file_io")] + fn auxv_dump_procfs() { + if let Ok(auxvec) = auxv_from_file("/proc/self/auxv") { + println!("{:?}", auxvec); + } else { + println!("reading /proc/self/auxv failed!"); + } + } + + #[cfg(any( + target_arch = "aarch64", + target_arch = "arm", + target_arch = "powerpc", + target_arch = "powerpc64", + target_arch = "s390x", + ))] + #[test] + #[cfg(feature = "std_detect_file_io")] + fn auxv_crate_procfs() { + if let Ok(procfs_auxv) = auxv_from_file("/proc/self/auxv") { + assert_eq!(auxv().unwrap(), procfs_auxv); + } + } +} |