4 files changed, 26 insertions, 11 deletions
diff --git a/compiler/rustc_target/src/asm/aarch64.rs b/compiler/rustc_target/src/asm/aarch64.rs
index b82d327a409..cdccb3e5d72 100644
--- a/compiler/rustc_target/src/asm/aarch64.rs
+++ b/compiler/rustc_target/src/asm/aarch64.rs
@@ -1,7 +1,7 @@
 use std::fmt;
 
 use rustc_data_structures::fx::FxIndexSet;
-use rustc_span::Symbol;
+use rustc_span::{Symbol, sym};
 
 use super::{InlineAsmArch, InlineAsmType, ModifierInfo};
 use crate::spec::{RelocModel, Target};
@@ -71,18 +71,26 @@ impl AArch64InlineAsmRegClass {
     }
 }
 
-pub(crate) fn target_reserves_x18(target: &Target) -> bool {
-    target.os == "android" || target.os == "fuchsia" || target.is_like_osx || target.is_like_windows
+pub(crate) fn target_reserves_x18(target: &Target, target_features: &FxIndexSet<Symbol>) -> bool {
+    // See isX18ReservedByDefault in LLVM for targets reserve x18 by default:
+    // https://github.com/llvm/llvm-project/blob/llvmorg-19.1.0/llvm/lib/TargetParser/AArch64TargetParser.cpp#L102-L105
+    // Note that +reserve-x18 is currently not set for the above targets.
+    target.os == "android"
+        || target.os == "fuchsia"
+        || target.env == "ohos"
+        || target.is_like_osx
+        || target.is_like_windows
+        || target_features.contains(&sym::reserve_x18)
 }
 
 fn reserved_x18(
     _arch: InlineAsmArch,
     _reloc_model: RelocModel,
-    _target_features: &FxIndexSet<Symbol>,
+    target_features: &FxIndexSet<Symbol>,
     target: &Target,
     _is_clobber: bool,
 ) -> Result<(), &'static str> {
-    if target_reserves_x18(target) {
+    if target_reserves_x18(target, target_features) {
         Err("x18 is a reserved register on this target")
     } else {
         Ok(())
diff --git a/compiler/rustc_target/src/asm/mod.rs b/compiler/rustc_target/src/asm/mod.rs
index c6ab5bed6d3..9fe733e063c 100644
--- a/compiler/rustc_target/src/asm/mod.rs
+++ b/compiler/rustc_target/src/asm/mod.rs
@@ -965,11 +965,13 @@ impl InlineAsmClobberAbi {
                 _ => Err(&["C", "system", "efiapi", "aapcs"]),
             },
             InlineAsmArch::AArch64 => match name {
-                "C" | "system" | "efiapi" => Ok(if aarch64::target_reserves_x18(target) {
-                    InlineAsmClobberAbi::AArch64NoX18
-                } else {
-                    InlineAsmClobberAbi::AArch64
-                }),
+                "C" | "system" | "efiapi" => {
+                    Ok(if aarch64::target_reserves_x18(target, target_features) {
+                        InlineAsmClobberAbi::AArch64NoX18
+                    } else {
+                        InlineAsmClobberAbi::AArch64
+                    })
+                }
                 _ => Err(&["C", "system", "efiapi"]),
             },
             InlineAsmArch::Arm64EC => match name {
diff --git a/compiler/rustc_target/src/spec/targets/aarch64_unknown_linux_ohos.rs b/compiler/rustc_target/src/spec/targets/aarch64_unknown_linux_ohos.rs
index 22b3a5f8842..14a22988a09 100644
--- a/compiler/rustc_target/src/spec/targets/aarch64_unknown_linux_ohos.rs
+++ b/compiler/rustc_target/src/spec/targets/aarch64_unknown_linux_ohos.rs
@@ -16,7 +16,6 @@ pub(crate) fn target() -> Target {
         data_layout: "e-m:e-p270:32:32-p271:32:32-p272:64:64-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128-Fn32".into(),
         arch: "aarch64".into(),
         options: TargetOptions {
-            features: "+reserve-x18".into(),
             mcount: "\u{1}_mcount".into(),
             stack_probes: StackProbeType::Inline,
             supported_sanitizers: SanitizerSet::ADDRESS
diff --git a/compiler/rustc_target/src/target_features.rs b/compiler/rustc_target/src/target_features.rs
index 112eb862663..67c047dddfc 100644
--- a/compiler/rustc_target/src/target_features.rs
+++ b/compiler/rustc_target/src/target_features.rs
@@ -228,6 +228,12 @@ const AARCH64_FEATURES: &[(&str, Stability, ImpliedFeatures)] = &[
     ("rcpc3", Unstable(sym::aarch64_unstable_target_feature), &["rcpc2"]),
     // FEAT_RDM
     ("rdm", Stable, &["neon"]),
+    // This is needed for inline assembly, but shouldn't be stabilized as-is
+    // since it should be enabled globally using -Zfixed-x18, not
+    // #[target_feature].
+    // Note that cfg(target_feature = "reserve-x18") is currently not set for
+    // targets that reserve x18 by default.
+    ("reserve-x18", Unstable(sym::aarch64_unstable_target_feature), &[]),
     // FEAT_SB
     ("sb", Stable, &[]),
     // FEAT_SHA1 & FEAT_SHA256