add repr to the allowlist for naked functions

compiler/rustc_passes/src/check_attr.rs

@@ -516,6 +516,7 @@ impl<'tcx> CheckAttrVisitor<'tcx> {
             sym::no_mangle,
             sym::naked,
             sym::instruction_set,
+            sym::repr,
             // code generation
             sym::cold,
             sym::target_feature,

tests/codegen/naked-fn/aligned.rs

@@ -0,0 +1,20 @@
+//@ compile-flags: -C no-prepopulate-passes -Copt-level=0
+//@ needs-asm-support
+//@ ignore-arm no "ret" mnemonic
+
+#![crate_type = "lib"]
+#![feature(naked_functions, fn_align)]
+use std::arch::asm;
+
+// CHECK: Function Attrs: naked
+// CHECK-NEXT: define{{.*}}void @naked_empty()
+// CHECK: align 16
+#[repr(align(16))]
+#[no_mangle]
+#[naked]
+pub unsafe extern "C" fn naked_empty() {
+    // CHECK-NEXT: start:
+    // CHECK-NEXT: call void asm
+    // CHECK-NEXT: unreachable
+    asm!("ret", options(noreturn));
+}

tests/ui/asm/naked-with-invalid-repr-attr.rs

@@ -0,0 +1,48 @@
+//@ needs-asm-support
+#![feature(naked_functions)]
+#![feature(fn_align)]
+#![crate_type = "lib"]
+use std::arch::asm;
+
+#[repr(C)]
+//~^ ERROR attribute should be applied to a struct, enum, or union [E0517]
+#[naked]
+extern "C" fn example1() {
+    //~^ NOTE not a struct, enum, or union
+    unsafe { asm!("", options(noreturn)) }
+}
+
+#[repr(transparent)]
+//~^ ERROR attribute should be applied to a struct, enum, or union [E0517]
+#[naked]
+extern "C" fn example2() {
+    //~^ NOTE not a struct, enum, or union
+    unsafe { asm!("", options(noreturn)) }
+}
+
+#[repr(align(16), C)]
+//~^ ERROR attribute should be applied to a struct, enum, or union [E0517]
+#[naked]
+extern "C" fn example3() {
+    //~^ NOTE not a struct, enum, or union
+    unsafe { asm!("", options(noreturn)) }
+}
+
+// note: two errors because of packed and C
+#[repr(C, packed)]
+//~^ ERROR attribute should be applied to a struct or union [E0517]
+//~| ERROR attribute should be applied to a struct, enum, or union [E0517]
+#[naked]
+extern "C" fn example4() {
+    //~^ NOTE not a struct, enum, or union
+    //~| NOTE not a struct or union
+    unsafe { asm!("", options(noreturn)) }
+}
+
+#[repr(u8)]
+//~^ ERROR attribute should be applied to an enum [E0517]
+#[naked]
+extern "C" fn example5() {
+    //~^ NOTE not an enum
+    unsafe { asm!("", options(noreturn)) }
+}

tests/ui/asm/naked-with-invalid-repr-attr.stderr

@@ -0,0 +1,77 @@
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/naked-with-invalid-repr-attr.rs:7:8
+   |
+LL |   #[repr(C)]
+   |          ^
+...
+LL | / extern "C" fn example1() {
+LL | |
+LL | |     unsafe { asm!("", options(noreturn)) }
+LL | | }
+   | |_- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/naked-with-invalid-repr-attr.rs:15:8
+   |
+LL |   #[repr(transparent)]
+   |          ^^^^^^^^^^^
+...
+LL | / extern "C" fn example2() {
+LL | |
+LL | |     unsafe { asm!("", options(noreturn)) }
+LL | | }
+   | |_- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/naked-with-invalid-repr-attr.rs:23:19
+   |
+LL |   #[repr(align(16), C)]
+   |                     ^
+...
+LL | / extern "C" fn example3() {
+LL | |
+LL | |     unsafe { asm!("", options(noreturn)) }
+LL | | }
+   | |_- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct, enum, or union
+  --> $DIR/naked-with-invalid-repr-attr.rs:32:8
+   |
+LL |   #[repr(C, packed)]
+   |          ^
+...
+LL | / extern "C" fn example4() {
+LL | |
+LL | |
+LL | |     unsafe { asm!("", options(noreturn)) }
+LL | | }
+   | |_- not a struct, enum, or union
+
+error[E0517]: attribute should be applied to a struct or union
+  --> $DIR/naked-with-invalid-repr-attr.rs:32:11
+   |
+LL |   #[repr(C, packed)]
+   |             ^^^^^^
+...
+LL | / extern "C" fn example4() {
+LL | |
+LL | |
+LL | |     unsafe { asm!("", options(noreturn)) }
+LL | | }
+   | |_- not a struct or union
+
+error[E0517]: attribute should be applied to an enum
+  --> $DIR/naked-with-invalid-repr-attr.rs:42:8
+   |
+LL |   #[repr(u8)]
+   |          ^^
+...
+LL | / extern "C" fn example5() {
+LL | |
+LL | |     unsafe { asm!("", options(noreturn)) }
+LL | | }
+   | |_- not an enum
+
+error: aborting due to 6 previous errors
+
+For more information about this error, try `rustc --explain E0517`.