From 531dae1cdfaea537f7f1d5ff7db6bd2adb4d414a Mon Sep 17 00:00:00 2001
From: bjorn3 <17426603+bjorn3@users.noreply.github.com>
Date: Sun, 12 May 2024 14:22:12 +0000
Subject: [PATCH] Only allow immutable statics with #[linkage]

---
 compiler/rustc_codegen_ssa/src/codegen_attrs.rs   | 12 ++++++++++++
 tests/ui/issues/issue-33992.rs                    |  3 ---
 .../linkage-attr/linkage-attr-mutable-static.rs   | 15 +++++++++++++++
 .../linkage-attr-mutable-static.stderr            | 10 ++++++++++
 4 files changed, 37 insertions(+), 3 deletions(-)
 create mode 100644 tests/ui/linkage-attr/linkage-attr-mutable-static.rs
 create mode 100644 tests/ui/linkage-attr/linkage-attr-mutable-static.stderr

diff --git a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs b/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
index c28b0d644e675..b479b0376684b 100644
--- a/compiler/rustc_codegen_ssa/src/codegen_attrs.rs
+++ b/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 => {
diff --git a/tests/ui/issues/issue-33992.rs b/tests/ui/issues/issue-33992.rs
index 177ff234bb291..495751436e127 100644
--- a/tests/ui/issues/issue-33992.rs
+++ b/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;
 
diff --git a/tests/ui/linkage-attr/linkage-attr-mutable-static.rs b/tests/ui/linkage-attr/linkage-attr-mutable-static.rs
new file mode 100644
index 0000000000000..a7109c6d930bc
--- /dev/null
+++ b/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);
+    }
+}
diff --git a/tests/ui/linkage-attr/linkage-attr-mutable-static.stderr b/tests/ui/linkage-attr/linkage-attr-mutable-static.stderr
new file mode 100644
index 0000000000000..4db41b6239382
--- /dev/null
+++ b/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
+