arm: use target.abi over soft-float target feature

Author: RalfJung

compiler/rustc_target/src/spec/mod.rs

@@ -3168,14 +3168,22 @@ impl Target {
                     self.llvm_abiname,
                 );
             }
-            "aarch64" => {
+            "aarch64" | "arm64ec" => {
                 check_matches!(
                     &*self.abi,
                     "softfloat" | "uwp" | "llvm" | "macabi" | "sim" | "ilp32" | "",
                     "invalid aarch64 ABI name: {}",
                     self.abi,
                 )
             }
+            "arm" => {
+                check_matches!(
+                    &*self.abi,
+                    "eabi" | "eabihf" | "uwp" | "macabi" | "sim" | "",
+                    "invalid aarch64 ABI name: {}",
+                    self.abi,
+                )
+            }
             _ => {}
         }
 

compiler/rustc_target/src/target_features.rs

@@ -759,6 +759,7 @@ impl Target {
         match &*self.arch {
             "x86" => {
                 // We support 2 ABIs, hardfloat (default) and softfloat.
+                // x86 has no sane ABI indicator so we have to use the target feature.
                 if self.has_feature("soft-float") {
                     NOTHING
                 } else {
@@ -768,6 +769,7 @@ impl Target {
             }
             "x86_64" => {
                 // We support 2 ABIs, hardfloat (default) and softfloat.
+                // x86 has no sane ABI indicator so we have to use the target feature.
                 if self.has_feature("soft-float") {
                     NOTHING
                 } else {
@@ -776,20 +778,20 @@ impl Target {
                 }
             }
             "arm" => {
-                // We support 2 ABIs, hardfloat (default) and softfloat.
-                if self.has_feature("soft-float") {
-                    NOTHING
-                } else {
-                    // Hardfloat ABI. x87 must be enabled.
-                    (&["fpregs"], &[])
+                // It's unclear how the `abi` and the `soft-float` target feature interact.
+                // We use the `abi` as our primary signal, and force `soft-float` to match.
+                match &*self.abi {
+                    "eabi" => (&["soft-float"], &[]),
+                    "eabihf" | "uwp" | "macabi" | "sim" | "" => (&["fpregs"], &["soft-float"]),
+                    _ => unreachable!(),
                 }
             }
             "aarch64" | "arm64ec" => {
                 match &*self.abi {
                     "softfloat" => {
                         // This is not fully correct, LLVM actually doesn't let us enforce the softfloat
                         // ABI properly... see <https://github.com/rust-lang/rust/issues/134375>.
-                        // FIXME: should be forbid "neon" here? But that would be a breaking change.
+                        // FIXME: should we forbid "neon" here? But that would be a breaking change.
                         NOTHING
                     }
                     "uwp" | "llvm" | "macabi" | "sim" | "ilp32" | "" => {