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fuchsia: dynamically enable fix-cortex-a53-835769 for generic CPUs #162566

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fuchsia: dynamically enable fix-cortex-a53-835769 for generic CPUs #162566

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14 changes: 13 additions & 1 deletion compiler/rustc_codegen_ssa/src/target_features.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ use rustc_middle::ty::TyCtxt;
use rustc_session::Session;
use rustc_session::diagnostics::feature_err;
use rustc_span::{Span, Symbol, edit_distance, sym};
use rustc_target::spec::{Arch, SanitizerSet};
use rustc_target::spec::{Arch, Os, SanitizerSet};
use rustc_target::target_features::{RUSTC_SPECIFIC_FEATURES, Stability};
use smallvec::SmallVec;

Expand Down Expand Up @@ -451,6 +451,18 @@ pub fn target_spec_to_backend_features<'a>(
extend_backend_features("ptx70", true);
}

// When targetting aarch64 Fuchsia, the +fix-cortex-a53-835769 should be applied by default
// whenever using the generic (armv8-a) CPU. This matches Clang's behavior for aarch64 Fuchsia.
if sess.target.os == Os::Fuchsia
&& sess.target.arch == Arch::AArch64
&& matches!(
sess.opts.cg.target_cpu.as_deref().unwrap_or(&sess.target.cpu),
"generic" | "cortex-a53"
)
{
extend_backend_features("fix-cortex-a53-835769", true);

@RalfJung RalfJung Sep 10, 2026 •
edited by rustbot
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This hack (wtf is even going on there) looks LLVM-specific but the file you put it in is also used for other backends.

View changes since the review

}

// Compute implied features
parse_rust_feature_list(
sess,
Expand Down
2 changes: 1 addition & 1 deletion compiler/rustc_target/src/spec/targets/aarch64_unknown_fuchsia.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -5,7 +5,7 @@ use crate::spec::{
pub(crate) fn target() -> Target {
let mut base = base::fuchsia::opts();
base.cpu = "generic".into();
base.features = "+v8a,+crc,+aes,+sha2,+neon,+fix-cortex-a53-835769".into();
base.features = "+v8a,+crc,+aes,+sha2,+neon".into();
base.max_atomic_width = Some(128);
base.stack_probes = StackProbeType::Inline;
base.supported_sanitizers = SanitizerSet::ADDRESS
Expand Down
13 changes: 12 additions & 1 deletion tests/codegen-llvm/aarch64-fuchsia-target-features.rs
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Original file line number Diff line number Diff line change
@@ -1,8 +1,19 @@
//@ add-minicore
//@ revisions: DEFAULT GENERIC A53 A73 A73_ENABLE DEFAULT_DISABLE
//@ compile-flags: --crate-type=rlib --target=aarch64-unknown-fuchsia
//@ needs-llvm-components: aarch64
//@ [GENERIC] compile-flags: -C target-cpu=generic
//@ [A53] compile-flags: -C target-cpu=cortex-a53
//@ [A73] compile-flags: -C target-cpu=cortex-a73
//@ [A73_ENABLE] compile-flags: -C target-cpu=cortex-a73 -C target-feature=+fix-cortex-a53-835769
//@ [DEFAULT_DISABLE] compile-flags: -C target-feature=-fix-cortex-a53-835769

// CHECK: attributes #0 = { {{.*}}"target-features"="{{.*}}+fix-cortex-a53-835769{{.*}}" }
// DEFAULT: attributes #0 = { {{.*}}"target-features"="{{.*}}+fix-cortex-a53-835769{{.*}}" }
// GENERIC: attributes #0 = { {{.*}}"target-features"="{{.*}}+fix-cortex-a53-835769{{.*}}" }
// A53: attributes #0 = { {{.*}}"target-features"="{{.*}}+fix-cortex-a53-835769{{.*}}" }
// A73-NOT: fix-cortex-a53-835769
// A73_ENABLE: attributes #0 = { {{.*}}"target-features"="{{.*}}+fix-cortex-a53-835769{{.*}}" }
// DEFAULT_DISABLE: attributes #0 = { {{.*}}"target-features"="{{.*}}-fix-cortex-a53-835769" }

#![feature(no_core, lang_items)]
#![no_core]
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