Add support for feature detection on FreeBSD/aarch64 (WIP)

crates/stdsimd/src/lib.rs

@@ -11,6 +11,7 @@
     deny(clippy::missing_inline_in_public_items,)
 )]
 #![cfg_attr(target_os = "linux", feature(linkage))]
+#![cfg_attr(all(target_os = "freebsd", target_arch = "aarch64"), feature(asm))]
 #![no_std]
 #![unstable(feature = "stdsimd", issue = "27731")]
 

stdsimd/arch/detect/mod.rs

@@ -71,6 +71,12 @@ cfg_if! {
     } else if #[cfg(target_os = "linux")] {
         #[path = "os/linux/mod.rs"]
         mod os;
+    } else if #[cfg(target_os = "freebsd")] {
+        #[cfg(target_arch = "aarch64")]
+        #[path = "os/aarch64.rs"]
+        mod aarch64;
+        #[path = "os/freebsd/mod.rs"]
+        mod os;
     } else {
         #[path = "os/other.rs"]
         mod os;

stdsimd/arch/detect/os/aarch64.rs

@@ -0,0 +1,80 @@
+//! Run-time feature detection for Aarch64 on any OS that emulates the mrs instruction.
+//!
+//! On FreeBSD >= 12.0, Linux >= 4.11 and other operating systems, it is possible to use
+//! privileged system registers from userspace to check CPU feature support.
+//!
+//! AArch64 system registers ID_AA64ISAR0_EL1, ID_AA64PFR0_EL1, ID_AA64ISAR1_EL1
+//! have bits dedicated to features like AdvSIMD, CRC32, AES, atomics (LSE), etc.
+//! Each part of the register indicates the level of support for a certain feature, e.g.
+//! when ID_AA64ISAR0_EL1[7:4] is >= 1, AES is supported; when it's >= 2, PMULL is supported.
+//!
+//! For proper support of [SoCs where different cores have different capabilities](https://medium.com/@jadr2ddude/a-big-little-problem-a-tale-of-big-little-gone-wrong-e7778ce744bb),
+//! the OS has to always report only the features supported by all cores, like [FreeBSD does](https://reviews.freebsd.org/D17137#393947).
+//!
+//! References:
+//!
+//! - [Zircon implementation](https://fuchsia.googlesource.com/zircon/+/master/kernel/arch/arm64/feature.cpp)
+//! - [Linux documentation](https://www.kernel.org/doc/Documentation/arm64/cpu-feature-registers.txt)
+
+use arch::detect::Feature;
+use arch::detect::cache;
+
+/// Try to read the features from the system registers.
+///
+/// This will cause SIGILL if the current OS is not trapping the mrs instruction.
+pub(crate) fn detect_features() -> cache::Initializer {
+    let mut value = cache::Initializer::default();
+
+    {
+        let mut enable_feature = |f, enable| {
+            if enable {
+                value.set(f as u32);
+            }
+        };
+
+        // ID_AA64ISAR0_EL1 - Instruction Set Attribute Register 0
+        let aa64isar0: u64;
+        unsafe { asm!("mrs $0, ID_AA64ISAR0_EL1" : "=r"(aa64isar0)); }
+
+        let aes = bits_shift(aa64isar0, 7, 4) >= 1;
+        let pmull = bits_shift(aa64isar0, 7, 4) >= 2;
+        let sha1 = bits_shift(aa64isar0, 11, 8) >= 1;
+        let sha2 = bits_shift(aa64isar0, 15, 12) >= 1;
+        enable_feature(Feature::pmull, pmull);
+        // Crypto is specified as AES + PMULL + SHA1 + SHA2 per LLVM/hosts.cpp
+        enable_feature(Feature::crypto, aes && pmull && sha1 && sha2);
+        enable_feature(Feature::lse, bits_shift(aa64isar0, 23, 20) >= 1);
+        enable_feature(Feature::crc, bits_shift(aa64isar0, 19, 16) >= 1);
+
+        // ID_AA64PFR0_EL1 - Processor Feature Register 0
+        let aa64pfr0: u64;
+        unsafe { asm!("mrs $0, ID_AA64PFR0_EL1" : "=r"(aa64pfr0)); }
+
+        let fp = bits_shift(aa64pfr0, 19, 16) < 0xF;
+        let fphp = bits_shift(aa64pfr0, 19, 16) >= 1;
+        let asimd = bits_shift(aa64pfr0, 23, 20) < 0xF;
+        let asimdhp = bits_shift(aa64pfr0, 23, 20) >= 1;
+        enable_feature(Feature::fp, fp);
+        enable_feature(Feature::fp16, fphp);
+        // SIMD support requires float support - if half-floats are
+        // supported, it also requires half-float support:
+        enable_feature(Feature::asimd, fp && asimd && (!fphp | asimdhp));
+        // SIMD extensions require SIMD support:
+        enable_feature(Feature::rdm, asimd && bits_shift(aa64isar0, 31, 28) >= 1);
+        enable_feature(Feature::dotprod, asimd && bits_shift(aa64isar0, 47, 44) >= 1);
+        enable_feature(Feature::sve, asimd && bits_shift(aa64pfr0, 35, 32) >= 1);
+
+        // ID_AA64ISAR1_EL1 - Instruction Set Attribute Register 1
+        let aa64isar1: u64;
+        unsafe { asm!("mrs $0, ID_AA64ISAR1_EL1" : "=r"(aa64isar1)); }
+
+        enable_feature(Feature::rcpc, bits_shift(aa64isar1, 23, 20) >= 1);
+    }
+
+    value
+}
+
+#[inline]
+fn bits_shift(x: u64, high: usize, low: usize) -> u64 {
+    (x >> low) & ((1 << (high - low + 1)) - 1)
+}

stdsimd/arch/detect/os/freebsd/aarch64.rs

@@ -0,0 +1,29 @@
+//! Run-time feature detection for Aarch64 on FreeBSD.
+
+use arch::detect::Feature;
+use arch::detect::cache;
+use super::super::aarch64::detect_features;
+
+/// Performs run-time feature detection.
+#[inline]
+pub fn check_for(x: Feature) -> bool {
+    cache::test(x as u32, detect_features)
+}
+
+#[cfg(test)]
+mod tests {
+    #[test]
+    fn dump() {
+        println!("asimd: {:?}", is_aarch64_feature_detected!("asimd"));
+        println!("pmull: {:?}", is_aarch64_feature_detected!("pmull"));
+        println!("fp: {:?}", is_aarch64_feature_detected!("fp"));
+        println!("fp16: {:?}", is_aarch64_feature_detected!("fp16"));
+        println!("sve: {:?}", is_aarch64_feature_detected!("sve"));
+        println!("crc: {:?}", is_aarch64_feature_detected!("crc"));
+        println!("crypto: {:?}", is_aarch64_feature_detected!("crypto"));
+        println!("lse: {:?}", is_aarch64_feature_detected!("lse"));
+        println!("rdm: {:?}", is_aarch64_feature_detected!("rdm"));
+        println!("rcpc: {:?}", is_aarch64_feature_detected!("rcpc"));
+        println!("dotprod: {:?}", is_aarch64_feature_detected!("dotprod"));
+    }
+}

stdsimd/arch/detect/os/freebsd/mod.rs

@@ -0,0 +1,14 @@
+//! Run-time feature detection on FreeBSD
+
+cfg_if! {
+    if #[cfg(target_arch = "aarch64")] {
+        mod aarch64;
+        pub use self::aarch64::check_for;
+    } else {
+        use arch::detect::Feature;
+        /// Performs run-time feature detection.
+        pub fn check_for(_x: Feature) -> bool {
+            false
+        }
+    }
+}