Auto merge of #142443 - matthiaskrgr:rollup-l1l6d0v, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - rust-lang/rust#128425 (Make `missing_fragment_specifier` an unconditional error)
 - rust-lang/rust#135927 (retpoline and retpoline-external-thunk flags (target modifiers) to enable retpoline-related target features)
 - rust-lang/rust#140770 (add `extern "custom"` functions)
 - rust-lang/rust#142176 (tests: Split dont-shuffle-bswaps along opt-levels and arches)
 - rust-lang/rust#142248 (Add supported asm types for LoongArch32)
 - rust-lang/rust#142267 (assert more in release in `rustc_ast_lowering`)
 - rust-lang/rust#142274 (Update the stdarch submodule)
 - rust-lang/rust#142276 (Update dependencies in `library/Cargo.lock`)
 - rust-lang/rust#142308 (Upgrade `object`, `addr2line`, and `unwinding` in the standard library)

Failed merges:

 - rust-lang/rust#140920 (Extract some shared code from codegen backend target feature handling)

r? `@ghost`
`@rustbot` modify labels: rollup

try-job: aarch64-apple
try-job: x86_64-msvc-1
try-job: x86_64-gnu
try-job: dist-i586-gnu-i586-i686-musl
try-job: test-various

4 files changed, 32 insertions, 2 deletions

diff --git a/compiler/rustc_hir_analysis/messages.ftl b/compiler/rustc_hir_analysis/messages.ftl
index 4fcd9f8a646..3e98bd213d3 100644
--- a/compiler/rustc_hir_analysis/messages.ftl
+++ b/compiler/rustc_hir_analysis/messages.ftl
@@ -1,3 +1,7 @@
+hir_analysis_abi_custom_clothed_function =
+    items with the `"custom"` ABI can only be declared externally or defined via naked functions
+    .suggestion = convert this to an `#[unsafe(naked)]` function
+
 hir_analysis_ambiguous_assoc_item = ambiguous associated {$assoc_kind} `{$assoc_ident}` in bounds of `{$qself}`
     .label = ambiguous associated {$assoc_kind} `{$assoc_ident}`
 
diff --git a/compiler/rustc_hir_analysis/src/check/check.rs b/compiler/rustc_hir_analysis/src/check/check.rs
index 60ca0155bdd..32fec0604c0 100644
--- a/compiler/rustc_hir_analysis/src/check/check.rs
+++ b/compiler/rustc_hir_analysis/src/check/check.rs
@@ -21,7 +21,7 @@ use rustc_middle::ty::error::TypeErrorToStringExt;
 use rustc_middle::ty::layout::{LayoutError, MAX_SIMD_LANES};
 use rustc_middle::ty::util::Discr;
 use rustc_middle::ty::{
-    AdtDef, BottomUpFolder, GenericArgKind, RegionKind, TypeFoldable, TypeSuperVisitable,
+    AdtDef, BottomUpFolder, FnSig, GenericArgKind, RegionKind, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitableExt, fold_regions,
 };
 use rustc_session::lint::builtin::UNINHABITED_STATIC;
@@ -100,6 +100,18 @@ pub fn check_abi_fn_ptr(tcx: TyCtxt<'_>, hir_id: hir::HirId, span: Span, abi: Ex
     }
 }
 
+pub fn check_custom_abi(tcx: TyCtxt<'_>, def_id: LocalDefId, fn_sig: FnSig<'_>, fn_sig_span: Span) {
+    if fn_sig.abi == ExternAbi::Custom {
+        // Function definitions that use `extern "custom"` must be naked functions.
+        if !tcx.has_attr(def_id, sym::naked) {
+            tcx.dcx().emit_err(crate::errors::AbiCustomClothedFunction {
+                span: fn_sig_span,
+                naked_span: tcx.def_span(def_id).shrink_to_lo(),
+            });
+        }
+    }
+}
+
 fn check_struct(tcx: TyCtxt<'_>, def_id: LocalDefId) {
     let def = tcx.adt_def(def_id);
     let span = tcx.def_span(def_id);
diff --git a/compiler/rustc_hir_analysis/src/check/mod.rs b/compiler/rustc_hir_analysis/src/check/mod.rs
index fad8abf5fae..c5c7e6b2aa7 100644
--- a/compiler/rustc_hir_analysis/src/check/mod.rs
+++ b/compiler/rustc_hir_analysis/src/check/mod.rs
@@ -72,7 +72,7 @@ pub mod wfcheck;
 
 use std::num::NonZero;
 
-pub use check::{check_abi, check_abi_fn_ptr};
+pub use check::{check_abi, check_abi_fn_ptr, check_custom_abi};
 use rustc_abi::{ExternAbi, VariantIdx};
 use rustc_data_structures::fx::{FxHashSet, FxIndexMap};
 use rustc_errors::{Diag, ErrorGuaranteed, pluralize, struct_span_code_err};
diff --git a/compiler/rustc_hir_analysis/src/errors.rs b/compiler/rustc_hir_analysis/src/errors.rs
index a27d1ed6c53..809cb311c1f 100644
--- a/compiler/rustc_hir_analysis/src/errors.rs
+++ b/compiler/rustc_hir_analysis/src/errors.rs
@@ -1698,3 +1698,17 @@ pub(crate) struct SelfInTypeAlias {
     #[label]
     pub span: Span,
 }
+
+#[derive(Diagnostic)]
+#[diag(hir_analysis_abi_custom_clothed_function)]
+pub(crate) struct AbiCustomClothedFunction {
+    #[primary_span]
+    pub span: Span,
+    #[suggestion(
+        hir_analysis_suggestion,
+        applicability = "maybe-incorrect",
+        code = "#[unsafe(naked)]\n",
+        style = "short"
+    )]
+    pub naked_span: Span,
+}