disallow export_name starting with "llvm."

Author: moxian

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -258,6 +258,17 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                         // so it may not contain any null characters.
                         tcx.dcx().emit_err(errors::NullOnExport { span: attr.span() });
                     }
+                    if s.as_str().starts_with("llvm."){
+                        let mut diag = tcx.dcx().struct_span_err(
+                            attr.value_span().expect("attibute has value but not a span"),
+                            "exported name must not start with \"llvm.\"",
+                        );
+                        diag.note(
+                            "symbols starting with \"llvm.\" are reserved for LLVM intrinsics \
+                            and cannot be defined in user code",
+                        );
+                        diag.emit();
+                    }
                     codegen_fn_attrs.export_name = Some(s);
                     mixed_export_name_no_mangle_lint_state.track_export_name(attr.span());
                 }

tests/ui/attributes/export_name-prefix.rs

@@ -0,0 +1,15 @@
+#![crate_type = "lib"]
+
+// rdtsc is an existing LLVM intrinsic
+#[export_name = "llvm.x86.rdtsc"]
+//~^ ERROR: exported name must not start with "llvm."
+pub unsafe fn foo(a: u8) -> u8 {
+    2 * a
+}
+
+// qwerty is not a real llvm intrinsic
+#[export_name = "llvm.x86.qwerty"]
+//~^ ERROR: exported name must not start with "llvm."
+pub unsafe fn bar(a: u8) -> u8 {
+    2 * a
+}

tests/ui/attributes/export_name-prefix.stderr

@@ -0,0 +1,18 @@
+error: exported name must not start with "llvm."
+  --> $DIR/export_name-prefix.rs:4:17
+   |
+LL | #[export_name = "llvm.x86.rdtsc"]
+   |                 ^^^^^^^^^^^^^^^^
+   |
+   = note: symbols starting with "llvm." are reserved for LLVM intrinsics and cannot be defined in user code
+
+error: exported name must not start with "llvm."
+  --> $DIR/export_name-prefix.rs:11:17
+   |
+LL | #[export_name = "llvm.x86.qwerty"]
+   |                 ^^^^^^^^^^^^^^^^^
+   |
+   = note: symbols starting with "llvm." are reserved for LLVM intrinsics and cannot be defined in user code
+
+error: aborting due to 2 previous errors
+