Add rustc_panic_entrypoint

Author: saethlin

compiler/rustc_attr_parsing/src/attributes/rustc_internal.rs

@@ -1246,6 +1246,15 @@ impl<S: Stage> NoArgsAttributeParser<S> for RustcIntrinsicConstStableIndirectPar
     const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcIntrinsicConstStableIndirect;
 }
 
+pub(crate) struct RustcPanicEntrypointParser;
+
+impl<S: Stage> NoArgsAttributeParser<S> for RustcPanicEntrypointParser {
+    const PATH: &[Symbol] = &[sym::rustc_panic_entrypoint];
+    const ON_DUPLICATE: OnDuplicate<S> = OnDuplicate::Error;
+    const ALLOWED_TARGETS: AllowedTargets = AllowedTargets::AllowList(&[Allow(Target::Fn)]);
+    const CREATE: fn(Span) -> AttributeKind = |_| AttributeKind::RustcPanicEntrypoint;
+}
+
 pub(crate) struct RustcStrictCoherenceParser;
 
 impl<S: Stage> NoArgsAttributeParser<S> for RustcStrictCoherenceParser {

compiler/rustc_attr_parsing/src/context.rs

@@ -299,6 +299,7 @@ attribute_parsers!(
         Single<WithoutArgs<RustcObjectLifetimeDefaultParser>>,
         Single<WithoutArgs<RustcOffloadKernelParser>>,
         Single<WithoutArgs<RustcOutlivesParser>>,
+        Single<WithoutArgs<RustcPanicEntrypointParser>>,
         Single<WithoutArgs<RustcPassIndirectlyInNonRusticAbisParser>>,
         Single<WithoutArgs<RustcPreserveUbChecksParser>>,
         Single<WithoutArgs<RustcProcMacroDeclsParser>>,

compiler/rustc_codegen_cranelift/src/base.rs

@@ -14,6 +14,7 @@ use rustc_middle::ty::layout::FnAbiOf;
 use rustc_middle::ty::print::with_no_trimmed_paths;
 use rustc_session::config::OutputFilenames;
 use rustc_span::Symbol;
+use rustc_target::spec::PanicStrategy;
 
 use crate::constant::ConstantCx;
 use crate::debuginfo::{FunctionDebugContext, TypeDebugContext};
@@ -384,6 +385,11 @@ fn codegen_fn_body(fx: &mut FunctionCx<'_, '_, '_>, start_block: Block) {
                 fx.bcx.switch_to_block(failure);
                 fx.bcx.ins().nop();
 
+                if fx.tcx.sess.panic_strategy() == PanicStrategy::ImmediateAbort {
+                    fx.bcx.ins().trap(TrapCode::user(1 /* unreachable */).unwrap());
+                    continue;
+                }
+
                 match &**msg {
                     AssertKind::BoundsCheck { len, index } => {
                         let len = codegen_operand(fx, len).load_scalar(fx);
@@ -1052,6 +1058,10 @@ pub(crate) fn codegen_panic_nounwind<'tcx>(
     msg_str: &str,
     span: Span,
 ) {
+    if fx.tcx.sess.panic_strategy() == PanicStrategy::ImmediateAbort {
+        fx.bcx.ins().trap(TrapCode::user(1 /* unreachable */).unwrap());
+    }
+
     let msg_ptr = crate::constant::pointer_for_anonymous_str(fx, msg_str);
     let msg_len = fx.bcx.ins().iconst(fx.pointer_type, i64::try_from(msg_str.len()).unwrap());
     let args = [msg_ptr, msg_len];

compiler/rustc_codegen_ssa/src/codegen_attrs.rs

@@ -4,7 +4,7 @@ use rustc_abi::{Align, ExternAbi};
 use rustc_ast::expand::autodiff_attrs::{AutoDiffAttrs, DiffActivity, DiffMode};
 use rustc_ast::{LitKind, MetaItem, MetaItemInner};
 use rustc_hir::attrs::{
-    AttributeKind, EiiImplResolution, InlineAttr, Linkage, RtsanSetting, UsedBy,
+    AttributeKind, EiiImplResolution, InlineAttr, Linkage, OptimizeAttr, RtsanSetting, UsedBy,
 };
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, LOCAL_CRATE, LocalDefId};
@@ -19,7 +19,7 @@ use rustc_middle::ty::{self as ty, TyCtxt};
 use rustc_session::lint;
 use rustc_session::parse::feature_err;
 use rustc_span::{Span, sym};
-use rustc_target::spec::Os;
+use rustc_target::spec::{Os, PanicStrategy};
 
 use crate::errors;
 use crate::target_features::{
@@ -391,6 +391,28 @@ fn apply_overrides(tcx: TyCtxt<'_>, did: LocalDefId, codegen_fn_attrs: &mut Code
             codegen_fn_attrs.flags |= CodegenFnAttrFlags::NO_MANGLE;
         }
     }
+
+    if tcx.is_panic_entrypoint(did) {
+        // Panic entrypoints are always cold.
+        //
+        // If we have immediate-abort enabled, we want panic entrypoints to be inlined. We have a
+        // MIR transform that tries to patch out immediate-abort panic entrypoint calls, but it can
+        // miss indirect calls. In such cases, this should encourage the optimizer to clean up the
+        // mess that we missed.
+        //
+        // When the panic strategies that support panic messages are enabled, we want panic
+        // entrypoints outlined and optimized for size.
+        // Most panic entrypoints want #[track_caller] but not all, so we do not add it.
+        // FIXME: It seems unlikely that all choices of #[track_caller] were deliberate, but it can
+        // have a code size impact, so it makes sense to apply judiciously.
+        codegen_fn_attrs.flags |= CodegenFnAttrFlags::COLD;
+        if tcx.sess.panic_strategy() == PanicStrategy::ImmediateAbort {
+            codegen_fn_attrs.inline = InlineAttr::Always;
+        } else {
+            codegen_fn_attrs.inline = InlineAttr::Never;
+            codegen_fn_attrs.optimize = OptimizeAttr::Size;
+        }
+    }
 }
 
 fn check_result(

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -15,6 +15,7 @@ use rustc_session::config::OptLevel;
 use rustc_span::Span;
 use rustc_span::source_map::Spanned;
 use rustc_target::callconv::{ArgAbi, ArgAttributes, CastTarget, FnAbi, PassMode};
+use rustc_target::spec::PanicStrategy;
 use tracing::{debug, info};
 
 use super::operand::OperandRef;
@@ -176,22 +177,22 @@ impl<'a, 'tcx> TerminatorCodegenHelper<'tcx> {
         if let Some(instance) = instance
             && is_call_from_compiler_builtins_to_upstream_monomorphization(tcx, instance)
         {
-            if destination.is_some() {
+            if tcx.is_panic_entrypoint(instance.def_id()) {
+                info!(
+                    "compiler_builtins call to panic entrypoint {:?} replaced with abort",
+                    instance.def_id()
+                );
+                bx.abort();
+                bx.unreachable();
+                return MergingSucc::False;
+            } else {
                 let caller_def = fx.instance.def_id();
                 let e = CompilerBuiltinsCannotCall {
                     span: tcx.def_span(caller_def),
                     caller: with_no_trimmed_paths!(tcx.def_path_str(caller_def)),
                     callee: with_no_trimmed_paths!(tcx.def_path_str(instance.def_id())),
                 };
                 tcx.dcx().emit_err(e);
-            } else {
-                info!(
-                    "compiler_builtins call to diverging function {:?} replaced with abort",
-                    instance.def_id()
-                );
-                bx.abort();
-                bx.unreachable();
-                return MergingSucc::False;
             }
         }
 
@@ -737,6 +738,12 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
         bx.switch_to_block(panic_block);
         self.set_debug_loc(bx, terminator.source_info);
 
+        if bx.tcx().sess.panic_strategy() == PanicStrategy::ImmediateAbort {
+            bx.abort();
+            bx.unreachable();
+            return MergingSucc::False;
+        }
+
         // Get the location information.
         let location = self.get_caller_location(bx, terminator.source_info).immediate();
 

compiler/rustc_feature/src/builtin_attrs.rs

@@ -1321,6 +1321,11 @@ pub static BUILTIN_ATTRIBUTES: &[BuiltinAttribute] = &[
         "`#[rustc_non_const_trait_method]` should only used by the standard library to mark trait methods \
         as non-const to allow large traits an easier transition to const"
     ),
+    rustc_attr!(
+        rustc_panic_entrypoint, AttributeType::Normal, template!(Word),
+        WarnFollowing, EncodeCrossCrate::Yes,
+        "`#[rustc_panic_entrypoint]` makes this function patchable by panic=immediate-abort",
+    ),
 
     BuiltinAttribute {
         name: sym::rustc_diagnostic_item,

compiler/rustc_hir/src/attrs/data_structures.rs

@@ -1283,6 +1283,9 @@ pub enum AttributeKind {
     /// Represents `#[rustc_outlives]`
     RustcOutlives,
 
+    /// Represents `#[rustc_panic_entrypoint]`
+    RustcPanicEntrypoint,
+
     /// Represents `#[rustc_paren_sugar]`.
     RustcParenSugar(Span),
 

compiler/rustc_hir/src/attrs/encode_cross_crate.rs

@@ -154,6 +154,7 @@ impl AttributeKind {
             RustcObjectLifetimeDefault => No,
             RustcOffloadKernel => Yes,
             RustcOutlives => No,
+            RustcPanicEntrypoint => Yes,
             RustcParenSugar(..) => No,
             RustcPassByValue(..) => Yes,
             RustcPassIndirectlyInNonRusticAbis(..) => No,

compiler/rustc_hir/src/lang_items.rs

@@ -235,6 +235,7 @@ language_item_table! {
     FnMut,                   sym::fn_mut,              fn_mut_trait,               Target::Trait,          GenericRequirement::Exact(1);
     FnOnce,                  sym::fn_once,             fn_once_trait,              Target::Trait,          GenericRequirement::Exact(1);
 
+    AbortIntrinsic,          sym::abort_intrinsic,     abort_intrinsic,            Target::Fn,             GenericRequirement::Exact(0);
     AsyncFn,                 sym::async_fn,            async_fn_trait,             Target::Trait,          GenericRequirement::Exact(1);
     AsyncFnMut,              sym::async_fn_mut,        async_fn_mut_trait,         Target::Trait,          GenericRequirement::Exact(1);
     AsyncFnOnce,             sym::async_fn_once,       async_fn_once_trait,        Target::Trait,          GenericRequirement::Exact(1);

compiler/rustc_lint/src/builtin.rs

@@ -25,7 +25,7 @@ use rustc_attr_parsing::AttributeParser;
 use rustc_errors::{Applicability, LintDiagnostic, msg};
 use rustc_feature::GateIssue;
 use rustc_hir as hir;
-use rustc_hir::attrs::{AttributeKind, DocAttribute};
+use rustc_hir::attrs::{AttributeKind, DocAttribute, InlineAttr};
 use rustc_hir::def::{DefKind, Res};
 use rustc_hir::def_id::{CRATE_DEF_ID, DefId, LocalDefId};
 use rustc_hir::intravisit::FnKind as HirFnKind;
@@ -3188,3 +3188,65 @@ impl EarlyLintPass for SpecialModuleName {
         }
     }
 }
+
+declare_lint! {
+    /// The `missing_panic_entrypoint` lint detects forgotten use of #[rustc_panic_entrypoint].
+    ///
+    /// This lint is intended to ensure that panic=immediate-abort can function as designed,
+    /// because it uses #[rustc_panic_entrypoint] to locate functions that should be outlined
+    /// for other panic modes, and be deleted entirely when immediate-abort is enabled.
+    pub MISSING_PANIC_ENTRYPOINT,
+    Allow,
+    "detects missing #[rustc_panic_entrypoint]"
+}
+
+declare_lint_pass!(MissingPanicEntrypoint => [MISSING_PANIC_ENTRYPOINT]);
+
+fn has_panic_entrypoint(attrs: &[hir::Attribute]) -> bool {
+    attrs
+        .iter()
+        .any(|attr| matches!(attr, hir::Attribute::Parsed(AttributeKind::RustcPanicEntrypoint)))
+}
+
+fn has_inline_encouragement(attrs: &[hir::Attribute]) -> bool {
+    attrs.iter().any(|attr| {
+        matches!(
+            attr,
+            hir::Attribute::Parsed(hir::attrs::AttributeKind::Inline(
+                InlineAttr::Hint | InlineAttr::Always | InlineAttr::Force { .. },
+                _
+            ))
+        )
+    })
+}
+
+fn has_rustc_intrinsic(attrs: &[hir::Attribute]) -> bool {
+    attrs.iter().any(|attr| matches!(attr, hir::Attribute::Parsed(AttributeKind::RustcIntrinsic)))
+}
+
+impl<'tcx> LateLintPass<'tcx> for MissingPanicEntrypoint {
+    fn check_fn(
+        &mut self,
+        cx: &LateContext<'tcx>,
+        _: HirFnKind<'tcx>,
+        fn_decl: &'tcx FnDecl<'tcx>,
+        _: &'tcx Body<'tcx>,
+        span: Span,
+        def_id: LocalDefId,
+    ) {
+        if matches!(fn_decl.output, hir::FnRetTy::Return(hir::Ty { kind: hir::TyKind::Never, .. }))
+        {
+            let attrs = cx.tcx.hir_attrs(cx.tcx.local_def_id_to_hir_id(def_id));
+            if has_rustc_intrinsic(attrs) {
+                return;
+            }
+            if !has_inline_encouragement(attrs) && !has_panic_entrypoint(attrs) {
+                cx.emit_span_lint(
+                    MISSING_PANIC_ENTRYPOINT,
+                    span,
+                    crate::lints::MissingPanicEntrypoint,
+                );
+            }
+        }
+    }
+}