Rollup merge of #125046 - bjorn3:no_mutable_static_linkage, r=cjgillot

Only allow immutable statics with #[linkage]

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -327,6 +327,18 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                     } else {
                         codegen_fn_attrs.linkage = linkage;
                     }
+                    if tcx.is_mutable_static(did.into()) {
+                        let mut diag = tcx.dcx().struct_span_err(
+                            attr.span,
+                            "mutable statics are not allowed with `#[linkage]`",
+                        );
+                        diag.note(
+                            "making the static mutable would allow changing which symbol the \
+                             static references rather than make the target of the symbol \
+                             mutable",
+                        );
+                        diag.emit();
+                    }
                 }
             }
             sym::link_section => {

tests/ui/issues/issue-33992.rs

@@ -5,9 +5,6 @@
 
 #![feature(linkage)]
 
-#[linkage = "common"]
-pub static mut TEST1: u32 = 0u32;
-
 #[linkage = "external"]
 pub static TEST2: bool = true;
 

tests/ui/linkage-attr/linkage-attr-mutable-static.rs

@@ -0,0 +1,15 @@
+//! The symbols are resolved by the linker. It doesn't make sense to change
+//! them at runtime, so deny mutable statics with #[linkage].
+
+#![feature(linkage)]
+
+fn main() {
+    extern "C" {
+        #[linkage = "weak"] //~ ERROR mutable statics are not allowed with `#[linkage]`
+        static mut ABC: *const u8;
+    }
+
+    unsafe {
+        assert_eq!(ABC as usize, 0);
+    }
+}

tests/ui/linkage-attr/linkage-attr-mutable-static.stderr

@@ -0,0 +1,10 @@
+error: mutable statics are not allowed with `#[linkage]`
+  --> $DIR/linkage-attr-mutable-static.rs:8:9
+   |
+LL |         #[linkage = "weak"]
+   |         ^^^^^^^^^^^^^^^^^^^
+   |
+   = note: making the static mutable would allow changing which symbol the static references rather than make the target of the symbol mutable
+
+error: aborting due to 1 previous error
+