Reject unsupported naked functions

Transition unsupported naked functions future incompatibility lint into
an error:

* Naked functions must contain a single inline assembly block.
  Introduced as future incompatibility lint in 1.50 rust-lang#79653.
  Change into an error fixes a soundness issue described in rust-lang#32489.

* Naked functions must not use any forms of inline attribute.
  Introduced as future incompatibility lint in 1.56 rust-lang#87652.

Author: tmiasko

compiler/rustc_error_codes/src/error_codes.rs

@@ -486,6 +486,7 @@ E0783: include_str!("./error_codes/E0783.md"),
 E0784: include_str!("./error_codes/E0784.md"),
 E0785: include_str!("./error_codes/E0785.md"),
 E0786: include_str!("./error_codes/E0786.md"),
+E0787: include_str!("./error_codes/E0787.md"),
 ;
 //  E0006, // merged with E0005
 //  E0008, // cannot bind by-move into a pattern guard

compiler/rustc_error_codes/src/error_codes/E0787.md

@@ -0,0 +1,28 @@
+An unsupported naked function definition.
+
+Erroneous code example:
+
+```compile_fail,E0787
+#![feature(naked_functions)]
+
+#[naked]
+pub extern "C" fn f() -> u32 {
+    42
+}
+```
+
+The naked functions must be defined using a single inline assembly
+block.
+
+The execution must never fall through past the end of the assembly
+code so the block must use `noreturn` option. The asm block can also
+use `att_syntax` and `raw` options, but others options are not allowed.
+
+The asm block must not contain any operands other than `const` and
+`sym`.
+
+### Additional information
+
+For more information, please see [RFC 2972].
+
+[RFC 2972]: https://github.com/rust-lang/rfcs/blob/master/text/2972-constrained-naked.md

compiler/rustc_lint/src/lib.rs

@@ -481,6 +481,11 @@ fn register_builtins(store: &mut LintStore, no_interleave_lints: bool) {
          <https://github.com/rust-lang/rust/issues/59014> for more information",
     );
     store.register_removed("plugin_as_library", "plugins have been deprecated and retired");
+    store.register_removed(
+        "unsupported_naked_functions",
+        "converted into hard error, see RFC 2972 \
+         <https://github.com/rust-lang/rfcs/blob/master/text/2972-constrained-naked.md> for more information",
+    );
 }
 
 fn register_internals(store: &mut LintStore) {

compiler/rustc_lint_defs/src/builtin.rs

@@ -2759,52 +2759,6 @@ declare_lint! {
     "undefined naked function ABI"
 }
 
-declare_lint! {
-    /// The `unsupported_naked_functions` lint detects naked function
-    /// definitions that are unsupported but were previously accepted.
-    ///
-    /// ### Example
-    ///
-    /// ```rust
-    /// #![feature(naked_functions)]
-    ///
-    /// #[naked]
-    /// pub extern "C" fn f() -> u32 {
-    ///     42
-    /// }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// The naked functions must be defined using a single inline assembly
-    /// block.
-    ///
-    /// The execution must never fall through past the end of the assembly
-    /// code so the block must use `noreturn` option. The asm block can also
-    /// use `att_syntax` option, but other options are not allowed.
-    ///
-    /// The asm block must not contain any operands other than `const` and
-    /// `sym`. Additionally, naked function should specify a non-Rust ABI.
-    ///
-    /// Naked functions cannot be inlined. All forms of the `inline` attribute
-    /// are prohibited.
-    ///
-    /// While other definitions of naked functions were previously accepted,
-    /// they are unsupported and might not work reliably. This is a
-    /// [future-incompatible] lint that will transition into hard error in
-    /// the future.
-    ///
-    /// [future-incompatible]: ../index.md#future-incompatible-lints
-    pub UNSUPPORTED_NAKED_FUNCTIONS,
-    Warn,
-    "unsupported naked function definitions",
-    @future_incompatible = FutureIncompatibleInfo {
-        reference: "issue #32408 <https://github.com/rust-lang/rust/issues/32408>",
-    };
-}
-
 declare_lint! {
     /// The `ineffective_unstable_trait_impl` lint detects `#[unstable]` attributes which are not used.
     ///
@@ -3070,7 +3024,6 @@ declare_lint_pass! {
         UNINHABITED_STATIC,
         FUNCTION_ITEM_REFERENCES,
         USELESS_DEPRECATED,
-        UNSUPPORTED_NAKED_FUNCTIONS,
         MISSING_ABI,
         INVALID_DOC_ATTRIBUTES,
         SEMICOLON_IN_EXPRESSIONS_FROM_MACROS,

compiler/rustc_passes/src/naked_functions.rs

@@ -1,14 +1,14 @@
 //! Checks validity of naked functions.
 
 use rustc_ast::{Attribute, InlineAsmOptions};
+use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def_id::LocalDefId;
 use rustc_hir::intravisit::{FnKind, Visitor};
 use rustc_hir::{ExprKind, HirId, InlineAsmOperand, StmtKind};
 use rustc_middle::ty::query::Providers;
 use rustc_middle::ty::TyCtxt;
 use rustc_session::lint::builtin::UNDEFINED_NAKED_FUNCTION_ABI;
-use rustc_session::lint::builtin::UNSUPPORTED_NAKED_FUNCTIONS;
 use rustc_span::symbol::sym;
 use rustc_span::Span;
 use rustc_target::spec::abi::Abi;
@@ -64,18 +64,16 @@ impl<'tcx> Visitor<'tcx> for CheckNakedFunctions<'tcx> {
             check_abi(self.tcx, hir_id, fn_header.abi, ident_span);
             check_no_patterns(self.tcx, body.params);
             check_no_parameters_use(self.tcx, body);
-            check_asm(self.tcx, hir_id, body, span);
-            check_inline(self.tcx, hir_id, attrs);
+            check_asm(self.tcx, body, span);
+            check_inline(self.tcx, attrs);
         }
     }
 }
 
 /// Check that the function isn't inlined.
-fn check_inline(tcx: TyCtxt<'_>, hir_id: HirId, attrs: &[Attribute]) {
+fn check_inline(tcx: TyCtxt<'_>, attrs: &[Attribute]) {
     for attr in attrs.iter().filter(|attr| attr.has_name(sym::inline)) {
-        tcx.struct_span_lint_hir(UNSUPPORTED_NAKED_FUNCTIONS, hir_id, attr.span, |lint| {
-            lint.build("naked functions cannot be inlined").emit();
-        });
+        tcx.sess.struct_span_err(attr.span, "naked functions cannot be inlined").emit();
     }
 }
 
@@ -146,31 +144,31 @@ impl<'tcx> Visitor<'tcx> for CheckParameters<'tcx> {
 }
 
 /// Checks that function body contains a single inline assembly block.
-fn check_asm<'tcx>(tcx: TyCtxt<'tcx>, hir_id: HirId, body: &'tcx hir::Body<'tcx>, fn_span: Span) {
+fn check_asm<'tcx>(tcx: TyCtxt<'tcx>, body: &'tcx hir::Body<'tcx>, fn_span: Span) {
     let mut this = CheckInlineAssembly { tcx, items: Vec::new() };
     this.visit_body(body);
     if let [(ItemKind::Asm, _)] = this.items[..] {
         // Ok.
     } else {
-        tcx.struct_span_lint_hir(UNSUPPORTED_NAKED_FUNCTIONS, hir_id, fn_span, |lint| {
-            let mut diag = lint.build("naked functions must contain a single asm block");
-            let mut has_asm = false;
-            for &(kind, span) in &this.items {
-                match kind {
-                    ItemKind::Asm if has_asm => {
-                        diag.span_label(
-                            span,
-                            "multiple asm blocks are unsupported in naked functions",
-                        );
-                    }
-                    ItemKind::Asm => has_asm = true,
-                    ItemKind::NonAsm => {
-                        diag.span_label(span, "non-asm is unsupported in naked functions");
-                    }
+        let mut diag = struct_span_err!(
+            tcx.sess,
+            fn_span,
+            E0787,
+            "naked functions must contain a single asm block"
+        );
+        let mut has_asm = false;
+        for &(kind, span) in &this.items {
+            match kind {
+                ItemKind::Asm if has_asm => {
+                    diag.span_label(span, "multiple asm blocks are unsupported in naked functions");
+                }
+                ItemKind::Asm => has_asm = true,
+                ItemKind::NonAsm => {
+                    diag.span_label(span, "non-asm is unsupported in naked functions");
                 }
             }
-            diag.emit();
-        });
+        }
+        diag.emit();
     }
 }
 
@@ -221,7 +219,7 @@ impl<'tcx> CheckInlineAssembly<'tcx> {
 
             ExprKind::InlineAsm(ref asm) => {
                 self.items.push((ItemKind::Asm, span));
-                self.check_inline_asm(expr.hir_id, asm, span);
+                self.check_inline_asm(asm, span);
             }
 
             ExprKind::DropTemps(..) | ExprKind::Block(..) | ExprKind::Err => {
@@ -230,7 +228,7 @@ impl<'tcx> CheckInlineAssembly<'tcx> {
         }
     }
 
-    fn check_inline_asm(&self, hir_id: HirId, asm: &'tcx hir::InlineAsm<'tcx>, span: Span) {
+    fn check_inline_asm(&self, asm: &'tcx hir::InlineAsm<'tcx>, span: Span) {
         let unsupported_operands: Vec<Span> = asm
             .operands
             .iter()
@@ -243,15 +241,13 @@ impl<'tcx> CheckInlineAssembly<'tcx> {
             })
             .collect();
         if !unsupported_operands.is_empty() {
-            self.tcx.struct_span_lint_hir(
-                UNSUPPORTED_NAKED_FUNCTIONS,
-                hir_id,
+            struct_span_err!(
+                self.tcx.sess,
                 unsupported_operands,
-                |lint| {
-                    lint.build("only `const` and `sym` operands are supported in naked functions")
-                        .emit();
-                },
-            );
+                E0787,
+                "only `const` and `sym` operands are supported in naked functions",
+            )
+            .emit();
         }
 
         let unsupported_options: Vec<&'static str> = [
@@ -266,19 +262,24 @@ impl<'tcx> CheckInlineAssembly<'tcx> {
         .collect();
 
         if !unsupported_options.is_empty() {
-            self.tcx.struct_span_lint_hir(UNSUPPORTED_NAKED_FUNCTIONS, hir_id, span, |lint| {
-                lint.build(&format!(
-                    "asm options unsupported in naked functions: {}",
-                    unsupported_options.join(", ")
-                ))
-                .emit();
-            });
+            struct_span_err!(
+                self.tcx.sess,
+                span,
+                E0787,
+                "asm options unsupported in naked functions: {}",
+                unsupported_options.join(", ")
+            )
+            .emit();
         }
 
         if !asm.options.contains(InlineAsmOptions::NORETURN) {
-            self.tcx.struct_span_lint_hir(UNSUPPORTED_NAKED_FUNCTIONS, hir_id, span, |lint| {
-                lint.build("asm in naked functions must use `noreturn` option").emit();
-            });
+            struct_span_err!(
+                self.tcx.sess,
+                span,
+                E0787,
+                "asm in naked functions must use `noreturn` option"
+            )
+            .emit();
         }
     }
 }

src/test/codegen/naked-functions.rs

@@ -1,42 +1,32 @@
 // compile-flags: -C no-prepopulate-passes
+// needs-asm-support
+// only-x86_64
 
 #![crate_type = "lib"]
 #![feature(naked_functions)]
+use std::arch::asm;
 
 // CHECK: Function Attrs: naked
 // CHECK-NEXT: define{{.*}}void @naked_empty()
 #[no_mangle]
 #[naked]
-pub fn naked_empty() {
+pub unsafe extern "C" fn naked_empty() {
     // CHECK-NEXT: {{.+}}:
-    // CHECK-NEXT: ret void
+    // CHECK-NEXT: call void asm
+    // CHECK-NEXT: unreachable
+    asm!("ret",
+         options(noreturn));
 }
 
 // CHECK: Function Attrs: naked
+// CHECK-NEXT: define{{.*}}i{{[0-9]+}} @naked_with_args_and_return(i64 %a, i64 %b)
 #[no_mangle]
 #[naked]
-// CHECK-NEXT: define{{.*}}void @naked_with_args(i{{[0-9]+( %a)?}})
-pub fn naked_with_args(a: isize) {
+pub unsafe extern "C" fn naked_with_args_and_return(a: isize, b: isize) -> isize {
     // CHECK-NEXT: {{.+}}:
-    // CHECK: ret void
-}
-
-// CHECK: Function Attrs: naked
-// CHECK-NEXT: define{{.*}}i{{[0-9]+}} @naked_with_return()
-#[no_mangle]
-#[naked]
-pub fn naked_with_return() -> isize {
-    // CHECK-NEXT: {{.+}}:
-    // CHECK-NEXT: ret i{{[0-9]+}} 0
-    0
-}
-
-// CHECK: Function Attrs: naked
-// CHECK-NEXT: define{{.*}}i{{[0-9]+}} @naked_with_args_and_return(i{{[0-9]+( %a)?}})
-#[no_mangle]
-#[naked]
-pub fn naked_with_args_and_return(a: isize) -> isize {
-    // CHECK-NEXT: {{.+}}:
-    // CHECK: ret i{{[0-9]+}} 0
-    0
+    // CHECK-NEXT: call void asm
+    // CHECK-NEXT: unreachable
+    asm!("lea rax, [rdi + rsi]",
+         "ret",
+         options(noreturn));
 }

src/test/codegen/naked-noinline.rs

@@ -7,7 +7,6 @@
 
 use std::arch::asm;
 
-#[inline(always)]
 #[naked]
 #[no_mangle]
 pub unsafe extern "C" fn f() {