disallow export_name starting with "llvm."

Author: moxian

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

@@ -258,6 +258,15 @@ 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.") {
+                        // 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: attr.value_span().expect("attibute has value but not a span"),
+                        });
+                    }
                     codegen_fn_attrs.export_name = Some(s);
                     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 {

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:17:1
+   |
+LL | #[export_name="ab\0cd"]
+   | ^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0648`.