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

Rollup merge of #125046 - bjorn3:no_mutable_static_linkage, r=cjgillot · rust-lang/rust@5860d43

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Original file line number	Diff line number	Diff line change
`@@ -327,6 +327,18 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {`
`327`	`327`	`} else {`
`328`	`328`	`codegen_fn_attrs.linkage = linkage;`
`329`	`329`	`}`
	`330`	`+if tcx.is_mutable_static(did.into()) {`
	`331`	`+let mut diag = tcx.dcx().struct_span_err(`
	`332`	`+ attr.span,`
	`333`	+"mutable statics are not allowed with `#[linkage]`",
	`334`	`+);`
	`335`	`+ diag.note(`
	`336`	`+"making the static mutable would allow changing which symbol the \`
	`337`	`+ static references rather than make the target of the symbol \`
	`338`	`+ mutable",`
	`339`	`+);`
	`340`	`+ diag.emit();`
	`341`	`+}`
`330`	`342`	`}`
`331`	`343`	`}`
`332`	`344`	`sym::link_section => {`

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,15 @@`
	`1`	`+//! The symbols are resolved by the linker. It doesn't make sense to change`
	`2`	`+//! them at runtime, so deny mutable statics with #[linkage].`
	`3`	`+`
	`4`	`+#![feature(linkage)]`
	`5`	`+`
	`6`	`+fn main() {`
	`7`	`+extern "C" {`
	`8`	+#[linkage = "weak"] //~ ERROR mutable statics are not allowed with `#[linkage]`
	`9`	`+static mut ABC: *const u8;`
	`10`	`+}`
	`11`	`+`
	`12`	`+unsafe {`
	`13`	`+assert_eq!(ABC as usize, 0);`
	`14`	`+}`
	`15`	`+}`

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,10 @@`
	`1`	+error: mutable statics are not allowed with `#[linkage]`
	`2`	`+ --> $DIR/linkage-attr-mutable-static.rs:8:9`
	`3`	`+ \|`
	`4`	`+LL \| #[linkage = "weak"]`
	`5`	`+ \| ^^^^^^^^^^^^^^^^^^^`
	`6`	`+ \|`
	`7`	`+ = note: making the static mutable would allow changing which symbol the static references rather than make the target of the symbol mutable`
	`8`	`+`
	`9`	`+error: aborting due to 1 previous error`
	`10`	`+`