3 files changed, 22 insertions, 1 deletions
diff --git a/compiler/rustc_session/src/errors.rs b/compiler/rustc_session/src/errors.rs
index 15bbd4ff7bf..8f671183fac 100644
--- a/compiler/rustc_session/src/errors.rs
+++ b/compiler/rustc_session/src/errors.rs
@@ -484,3 +484,14 @@ pub(crate) struct FunctionReturnThunkExternRequiresNonLargeCodeModel;
 pub(crate) struct FailedToCreateProfiler {
     pub(crate) err: String,
 }
+
+#[derive(Diagnostic)]
+#[diag(session_soft_float_ignored)]
+#[note]
+pub(crate) struct SoftFloatIgnored;
+
+#[derive(Diagnostic)]
+#[diag(session_soft_float_deprecated)]
+#[note]
+#[note(session_soft_float_deprecated_issue)]
+pub(crate) struct SoftFloatDeprecated;
diff --git a/compiler/rustc_session/src/options.rs b/compiler/rustc_session/src/options.rs
index 37077901e0c..4427cf346bb 100644
--- a/compiler/rustc_session/src/options.rs
+++ b/compiler/rustc_session/src/options.rs
@@ -1615,7 +1615,7 @@ options! {
     save_temps: bool = (false, parse_bool, [UNTRACKED],
         "save all temporary output files during compilation (default: no)"),
     soft_float: bool = (false, parse_bool, [TRACKED],
-        "use soft float ABI (*eabihf targets only) (default: no)"),
+        "deprecated option: use soft float ABI (*eabihf targets only) (default: no)"),
     #[rustc_lint_opt_deny_field_access("use `Session::split_debuginfo` instead of this field")]
     split_debuginfo: Option<SplitDebuginfo> = (None, parse_split_debuginfo, [TRACKED],
         "how to handle split-debuginfo, a platform-specific option"),
diff --git a/compiler/rustc_session/src/session.rs b/compiler/rustc_session/src/session.rs
index 70430d82ab5..9b3348c3969 100644
--- a/compiler/rustc_session/src/session.rs
+++ b/compiler/rustc_session/src/session.rs
@@ -1340,6 +1340,16 @@ fn validate_commandline_args_with_session_available(sess: &Session) {
             }
         }
     }
+
+    if sess.opts.cg.soft_float {
+        if sess.target.arch == "arm" && sess.target.abi == "eabihf" {
+            sess.dcx().emit_warn(errors::SoftFloatDeprecated);
+        } else {
+            // All `use_softfp` does is the equivalent of `-mfloat-abi` in GCC/clang, which only exists on ARM targets.
+            // We document this flag to only affect `*eabihf` targets, so let's show a warning for all other targets.
+            sess.dcx().emit_warn(errors::SoftFloatIgnored);
+        }
+    }
 }
 
 /// Holds data on the current incremental compilation session, if there is one.