Disallow export_name starting with "llvm."

compiler/rustc_codegen_ssa/messages.ftl

@@ -52,6 +52,9 @@ codegen_ssa_expected_one_argument = expected one argument
 
 codegen_ssa_expected_used_symbol = expected `used`, `used(compiler)` or `used(linker)`
 
+codegen_ssa_export_name_llvm_intrinsic = exported symbol name must not start with "llvm."
+    .note = symbols starting with "llvm." are reserved for LLVM intrinsics and cannot be defined in user code
+
 codegen_ssa_extern_funcs_not_found = some `extern` functions couldn't be found; some native libraries may need to be installed or have their path specified
 
 codegen_ssa_extract_bundled_libs_archive_member = failed to get data from archive member '{$rlib}': {$error}

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -252,13 +252,21 @@ fn codegen_fn_attrs(tcx: TyCtxt<'_>, did: LocalDefId) -> CodegenFnAttrs {
                 codegen_fn_attrs.flags |= CodegenFnAttrFlags::TRACK_CALLER
             }
             sym::export_name => {
-                if let Some(s) = attr.value_str() {
-                    if s.as_str().contains('\0') {
+                if let Some(exported_name) = attr.value_str() {
+                    let value_span = attr.value_span().expect("attibute has value but not a span");
+                    if exported_name.as_str().contains('\0') {
                         // `#[export_name = ...]` will be converted to a null-terminated string,
                         // so it may not contain any null characters.
-                        tcx.dcx().emit_err(errors::NullOnExport { span: attr.span() });
+                        tcx.dcx().emit_err(errors::NullOnExport { span: value_span });
                     }
-                    codegen_fn_attrs.export_name = Some(s);
+                    if exported_name.as_str().starts_with("llvm.") {
+                        // Symbols starting with "llvm." are reserved by LLVM
+                        // trying to define those would produce invalid IR.
+                        // LLVM complain about those *if* we enable LLVM verification checks
+                        // but we often don't enable them by default due to perf reasons.
+                        tcx.dcx().emit_err(errors::ExportNameLLVMIntrinsic { span: value_span });
+                    }
+                    codegen_fn_attrs.export_name = Some(exported_name);
                     mixed_export_name_no_mangle_lint_state.track_export_name(attr.span());
                 }
             }

compiler/rustc_codegen_ssa/src/errors.rs

@@ -147,6 +147,14 @@ pub(crate) struct NullOnExport {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(codegen_ssa_export_name_llvm_intrinsic)]
+#[note]
+pub(crate) struct ExportNameLLVMIntrinsic {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(codegen_ssa_unsupported_instruction_set, code = E0779)]
 pub(crate) struct UnsuportedInstructionSet {

compiler/rustc_errors/src/lib.rs

@@ -1304,7 +1304,6 @@ impl<'a> DiagCtxtHandle<'a> {
         self.create_almost_fatal(fatal).emit()
     }
 
-    // FIXME: This method should be removed (every error should have an associated error code).
     #[rustc_lint_diagnostics]
     #[track_caller]
     pub fn struct_err(self, msg: impl Into<DiagMessage>) -> Diag<'a> {

tests/ui/attributes/export_name-checks.rs

@@ -0,0 +1,18 @@
+#![crate_type = "lib"]
+
+// rdtsc is an existing LLVM intrinsic
+#[export_name = "llvm.x86.rdtsc"]
+//~^ ERROR: exported symbol 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 symbol name must not start with "llvm."
+pub unsafe fn bar(a: u8) -> u8 {
+    2 * a
+}
+
+#[export_name="ab\0cd"] //~ ERROR `export_name` may not contain null characters
+pub fn qux() {}

tests/ui/attributes/export_name-checks.stderr

@@ -0,0 +1,25 @@
+error: exported symbol name must not start with "llvm."
+  --> $DIR/export_name-checks.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 symbol name must not start with "llvm."
+  --> $DIR/export_name-checks.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[E0648]: `export_name` may not contain null characters
+  --> $DIR/export_name-checks.rs:17:15
+   |
+LL | #[export_name="ab\0cd"]
+   |               ^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0648`.

tests/ui/error-codes/E0648.stderr

@@ -1,8 +1,8 @@
 error[E0648]: `export_name` may not contain null characters
-  --> $DIR/E0648.rs:1:1
+  --> $DIR/E0648.rs:1:15
    |
 LL | #[export_name="\0foo"]
-   | ^^^^^^^^^^^^^^^^^^^^^^
+   |               ^^^^^^^
 
 error: aborting due to 1 previous error