Enable sha1 AArch64 extension on Linux

The feature gate is specific to glibc on Linux, using getauxval() to
check the CPU flags, so it’s currently not used on other systems.
Patches welcome. :)

Enables RustCrypto/asm-hashes#10

Author: linkmauve

sha1/src/aarch64.rs

@@ -0,0 +1,11 @@
+// From sys/auxv.h
+const AT_HWCAP: u64 = 16;
+const HWCAP_SHA1: u64 = 32;
+extern {
+    fn getauxval(type_: u64) -> u64;
+}
+
+pub fn sha1_supported() -> bool {
+    let hwcaps: u64 = unsafe { getauxval(AT_HWCAP) };
+    (hwcaps & HWCAP_SHA1) != 0
+}

sha1/src/consts.rs

@@ -2,16 +2,16 @@
 
 pub const STATE_LEN: usize = 5;
 
-#[cfg(not(feature = "asm"))]
+#[cfg(any(not(feature = "asm"), all(target_arch = "aarch64", target_os = "linux")))]
 pub const BLOCK_LEN: usize = 16;
 
-#[cfg(not(feature = "asm"))]
+#[cfg(any(not(feature = "asm"), all(target_arch = "aarch64", target_os = "linux")))]
 pub const K0: u32 = 0x5A827999u32;
-#[cfg(not(feature = "asm"))]
+#[cfg(any(not(feature = "asm"), all(target_arch = "aarch64", target_os = "linux")))]
 pub const K1: u32 = 0x6ED9EBA1u32;
-#[cfg(not(feature = "asm"))]
+#[cfg(any(not(feature = "asm"), all(target_arch = "aarch64", target_os = "linux")))]
 pub const K2: u32 = 0x8F1BBCDCu32;
-#[cfg(not(feature = "asm"))]
+#[cfg(any(not(feature = "asm"), all(target_arch = "aarch64", target_os = "linux")))]
 pub const K3: u32 = 0xCA62C1D6u32;
 
 pub const H: [u32; STATE_LEN] = [

sha1/src/lib.rs

@@ -33,19 +33,34 @@ extern crate block_buffer;
 #[macro_use] pub extern crate digest;
 #[cfg(feature = "std")]
 extern crate std;
-#[cfg(not(feature = "asm"))]
+#[cfg(any(not(feature = "asm"), all(target_arch = "aarch64", target_os = "linux")))]
 extern crate fake_simd as simd;
 
 #[cfg(feature = "asm")]
 extern crate sha1_asm;
-#[cfg(feature = "asm")]
+#[cfg(all(feature = "asm", not(all(target_arch = "aarch64", target_os = "linux"))))]
 #[inline(always)]
 fn compress(state: &mut [u32; 5], block: &GenericArray<u8, U64>) {
     let block: &[u8; 64] = unsafe { core::mem::transmute(block) };
     sha1_asm::compress(state, block);
 }
+#[cfg(all(feature = "asm", target_arch = "aarch64", target_os = "linux"))]
+mod aarch64;
+#[cfg(all(feature = "asm", target_arch = "aarch64", target_os = "linux"))]
+#[inline(always)]
+fn compress(state: &mut [u32; 5], block: &GenericArray<u8, U64>) {
+    // TODO: Replace this platform-specific call with is_aarch64_feature_detected!("sha1") once
+    // that macro is stabilised and https://github.com/rust-lang/rfcs/pull/2725 is implemented
+    // to let us use it on no_std.
+    if aarch64::sha1_supported() {
+        let block: &[u8; 64] = unsafe { core::mem::transmute(block) };
+        sha1_asm::compress(state, block);
+    } else {
+        utils::compress(state, block);
+    }
+}
 
-#[cfg(not(feature = "asm"))]
+#[cfg(any(not(feature = "asm"), all(target_arch = "aarch64", target_os = "linux")))]
 mod utils;
 #[cfg(not(feature = "asm"))]
 use utils::compress;