x86: rust: set rustc-abi=x86-softfloat on rustc>=1.86.0

commit 6273a05 upstream.

When using Rust on the x86 architecture, we are currently using the
unstable target.json feature to specify the compilation target. Rustc is
going to change how softfloat is specified in the target.json file on
x86, thus update generate_rust_target.rs to specify softfloat using the
new option.

Note that if you enable this parameter with a compiler that does not
recognize it, then that triggers a warning but it does not break the
build.

[ For future reference, this solves the following error:

        RUSTC L rust/core.o
      error: Error loading target specification: target feature
      `soft-float` is incompatible with the ABI but gets enabled in
      target spec. Run `rustc --print target-list` for a list of
      built-in targets

  - Miguel ]

Cc: <[email protected]> # Needed in 6.12.y and 6.13.y only (Rust is pinned in older LTSs).
Link: rust-lang/rust#136146
Signed-off-by: Alice Ryhl <[email protected]>
Acked-by: Dave Hansen <[email protected]> # for x86
Link: https://lore.kernel.org/r/[email protected]
[ Added 6.13.y too to Cc: stable tag and added reasoning to avoid
  over-backporting. - Miguel ]
Signed-off-by: Miguel Ojeda <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>

scripts/generate_rust_target.rs

@@ -165,6 +165,18 @@ impl KernelConfig {
         let option = "CONFIG_".to_owned() + option;
         self.0.contains_key(&option)
     }
+
+    /// Is the rustc version at least `major.minor.patch`?
+    fn rustc_version_atleast(&self, major: u32, minor: u32, patch: u32) -> bool {
+        let check_version = 100000 * major + 100 * minor + patch;
+        let actual_version = self
+            .0
+            .get("CONFIG_RUSTC_VERSION")
+            .unwrap()
+            .parse::<u32>()
+            .unwrap();
+        check_version <= actual_version
+    }
 }
 
 fn main() {
@@ -182,6 +194,9 @@ fn main() {
         }
     } else if cfg.has("X86_64") {
         ts.push("arch", "x86_64");
+        if cfg.rustc_version_atleast(1, 86, 0) {
+            ts.push("rustc-abi", "x86-softfloat");
+        }
         ts.push(
             "data-layout",
             "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128",
@@ -215,6 +230,9 @@ fn main() {
             panic!("32-bit x86 only works under UML");
         }
         ts.push("arch", "x86");
+        if cfg.rustc_version_atleast(1, 86, 0) {
+            ts.push("rustc-abi", "x86-softfloat");
+        }
         ts.push(
             "data-layout",
             "e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-i128:128-f64:32:64-f80:32-n8:16:32-S128",