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cpufeatures: add Speculation Barrier (SB) support for AArch64 #1536

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Merged
tarcieri merged 1 commit into from
Sep 10, 2026
Merged

cpufeatures: add Speculation Barrier (SB) support for AArch64 #1536

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10 changes: 9 additions & 1 deletion cpufeatures/src/aarch64.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -67,10 +67,11 @@ macro_rules! __expand_check_macro {
#[cfg(any(target_os = "linux", target_os = "android"))]
__expand_check_macro! {
("aes", AES), // Enable AES support.
("dit", DIT), // Enable DIT support.
("dit", DIT), // Enable Data-Independent Timing support.
("sha2", SHA2), // Enable SHA1 and SHA256 support.
("sha3", SHA3), // Enable SHA512 and SHA3 support.
("sm4", SM4), // Enable SM3 and SM4 support.
("sb", SB), // Enable Speculation Barrier support
}

/// Linux hardware capabilities mapped to target features.
Expand All @@ -89,6 +90,7 @@ pub mod hwcaps {
pub const SHA2: c_ulong = libc::HWCAP_SHA2;
pub const SHA3: c_ulong = libc::HWCAP_SHA3 | libc::HWCAP_SHA512;
pub const SM4: c_ulong = libc::HWCAP_SM3 | libc::HWCAP_SM4;
pub const SB: c_ulong = libc::HWCAP_SB;
Comment on lines 74 to +93

@tarcieri tarcieri Sep 10, 2026

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Note: it's unclear to what extent either DIT or SB are helpful on non-Apple targets, as covered in #1472, but they've been added here (i.e. Linux) for completeness

}

// Apple OS (macOS, iOS, watchOS, and tvOS) `check!` macro.
Expand Down Expand Up @@ -128,6 +130,12 @@ macro_rules! check {
("sm4") => {
false
};
("sb") => {
// https://support.arm.com/documentation/ddi0487/mb/-Part-B-The-AArch64-Application-Level-Architecture/-Chapter-B2-The-AArch64-Application-Level-Memory-Model/-B2-6-Memory-barriers/-B2-6-3-Speculation-Barrier
unsafe {
$crate::aarch64::sysctlbyname(b"hw.optional.arm.FEAT_SB\0")
}
};
}

/// Apple helper function for calling `sysctlbyname`.
Expand Down