Auto merge of rust-lang#129949 - tgross35:rollup-352zljc, r=tgross35

Rollup of 8 pull requests

Successful merges:

 - rust-lang#101339 (enable -Zrandomize-layout in debug CI builds )
 - rust-lang#127021 (Add target support for RTEMS Arm)
 - rust-lang#128871 (bypass linker configuration and cross target check for specific commands)
 - rust-lang#129471 ([rustdoc] Sort impl associated items by kinds and then by appearance)
 - rust-lang#129529 (Add test to build crates used by r-a on stable)
 - rust-lang#129624 (Adjust `memchr` pinning and run `cargo update`)
 - rust-lang#129796 (Unify scraped examples with other code examples)
 - rust-lang#129939 (explain why Rvalue::Len still exists)

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

Author: bors

Cargo.lock

@@ -30,5 +30,6 @@ features = ['unprefixed_malloc_on_supported_platforms']
 jemalloc = ['dep:jemalloc-sys']
 llvm = ['rustc_driver_impl/llvm']
 max_level_info = ['rustc_driver_impl/max_level_info']
+rustc_randomized_layouts = ['rustc_driver_impl/rustc_randomized_layouts']
 rustc_use_parallel_compiler = ['rustc_driver_impl/rustc_use_parallel_compiler']
 # tidy-alphabetical-end

compiler/rustc/Cargo.toml

@@ -968,8 +968,8 @@ fn univariant<
     let mut align = if pack.is_some() { dl.i8_align } else { dl.aggregate_align };
     let mut max_repr_align = repr.align;
     let mut inverse_memory_index: IndexVec<u32, FieldIdx> = fields.indices().collect();
-    let optimize = !repr.inhibit_struct_field_reordering();
-    if optimize && fields.len() > 1 {
+    let optimize_field_order = !repr.inhibit_struct_field_reordering();
+    if optimize_field_order && fields.len() > 1 {
         let end = if let StructKind::MaybeUnsized = kind { fields.len() - 1 } else { fields.len() };
         let optimizing = &mut inverse_memory_index.raw[..end];
         let fields_excluding_tail = &fields.raw[..end];
@@ -1176,7 +1176,7 @@ fn univariant<
     // If field 5 has offset 0, offsets[0] is 5, and memory_index[5] should be 0.
     // Field 5 would be the first element, so memory_index is i:
     // Note: if we didn't optimize, it's already right.
-    let memory_index = if optimize {
+    let memory_index = if optimize_field_order {
         inverse_memory_index.invert_bijective_mapping()
     } else {
         debug_assert!(inverse_memory_index.iter().copied().eq(fields.indices()));
@@ -1189,6 +1189,9 @@ fn univariant<
     }
     let mut layout_of_single_non_zst_field = None;
     let mut abi = Abi::Aggregate { sized };
+
+    let optimize_abi = !repr.inhibit_newtype_abi_optimization();
+
     // Try to make this a Scalar/ScalarPair.
     if sized && size.bytes() > 0 {
         // We skip *all* ZST here and later check if we are good in terms of alignment.
@@ -1205,7 +1208,7 @@ fn univariant<
                     match field.abi {
                         // For plain scalars, or vectors of them, we can't unpack
                         // newtypes for `#[repr(C)]`, as that affects C ABIs.
-                        Abi::Scalar(_) | Abi::Vector { .. } if optimize => {
+                        Abi::Scalar(_) | Abi::Vector { .. } if optimize_abi => {
                             abi = field.abi;
                         }
                         // But scalar pairs are Rust-specific and get

compiler/rustc_abi/src/layout.rs

@@ -43,14 +43,17 @@ bitflags! {
         const IS_SIMD            = 1 << 1;
         const IS_TRANSPARENT     = 1 << 2;
         // Internal only for now. If true, don't reorder fields.
+        // On its own it does not prevent ABI optimizations.
         const IS_LINEAR          = 1 << 3;
-        // If true, the type's layout can be randomized using
-        // the seed stored in `ReprOptions.field_shuffle_seed`
+        // If true, the type's crate has opted into layout randomization.
+        // Other flags can still inhibit reordering and thus randomization.
+        // The seed stored in `ReprOptions.field_shuffle_seed`.
         const RANDOMIZE_LAYOUT   = 1 << 4;
         // Any of these flags being set prevent field reordering optimisation.
-        const IS_UNOPTIMISABLE   = ReprFlags::IS_C.bits()
+        const FIELD_ORDER_UNOPTIMIZABLE   = ReprFlags::IS_C.bits()
                                  | ReprFlags::IS_SIMD.bits()
                                  | ReprFlags::IS_LINEAR.bits();
+        const ABI_UNOPTIMIZABLE = ReprFlags::IS_C.bits() | ReprFlags::IS_SIMD.bits();
     }
 }
 
@@ -139,10 +142,14 @@ impl ReprOptions {
         self.c() || self.int.is_some()
     }
 
+    pub fn inhibit_newtype_abi_optimization(&self) -> bool {
+        self.flags.intersects(ReprFlags::ABI_UNOPTIMIZABLE)
+    }
+
     /// Returns `true` if this `#[repr()]` guarantees a fixed field order,
     /// e.g. `repr(C)` or `repr(<int>)`.
     pub fn inhibit_struct_field_reordering(&self) -> bool {
-        self.flags.intersects(ReprFlags::IS_UNOPTIMISABLE) || self.int.is_some()
+        self.flags.intersects(ReprFlags::FIELD_ORDER_UNOPTIMIZABLE) || self.int.is_some()
     }
 
     /// Returns `true` if this type is valid for reordering and `-Z randomize-layout`

compiler/rustc_abi/src/lib.rs

@@ -4,10 +4,9 @@ version = "0.0.0"
 edition = "2021"
 
 [dependencies]
-# FIXME: bumping memchr to 2.7.1 causes linker errors in MSVC thin-lto
 # tidy-alphabetical-start
 bitflags = "2.4.1"
-memchr = "=2.5.0"
+memchr = "2.7.4"
 rustc_ast_ir = { path = "../rustc_ast_ir" }
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_index = { path = "../rustc_index" }

compiler/rustc_ast/Cargo.toml

@@ -23,6 +23,7 @@ rustc_hir_analysis = { path = "../rustc_hir_analysis" }
 rustc_hir_pretty = { path = "../rustc_hir_pretty" }
 rustc_hir_typeck = { path = "../rustc_hir_typeck" }
 rustc_incremental = { path = "../rustc_incremental" }
+rustc_index = { path = "../rustc_index" }
 rustc_infer = { path = "../rustc_infer" }
 rustc_interface = { path = "../rustc_interface" }
 rustc_lint = { path = "../rustc_lint" }
@@ -72,6 +73,10 @@ ctrlc = "3.4.4"
 # tidy-alphabetical-start
 llvm = ['rustc_interface/llvm']
 max_level_info = ['rustc_log/max_level_info']
+rustc_randomized_layouts = [
+    'rustc_index/rustc_randomized_layouts',
+    'rustc_middle/rustc_randomized_layouts'
+]
 rustc_use_parallel_compiler = [
     'rustc_data_structures/rustc_use_parallel_compiler',
     'rustc_interface/rustc_use_parallel_compiler',

compiler/rustc_driver_impl/Cargo.toml

@@ -20,4 +20,5 @@ nightly = [
     "dep:rustc_macros",
     "rustc_index_macros/nightly",
 ]
+rustc_randomized_layouts = []
 # tidy-alphabetical-end

compiler/rustc_index/Cargo.toml

@@ -33,8 +33,19 @@ pub use vec::IndexVec;
 ///
 /// </div>
 #[macro_export]
+#[cfg(not(feature = "rustc_randomized_layouts"))]
 macro_rules! static_assert_size {
     ($ty:ty, $size:expr) => {
         const _: [(); $size] = [(); ::std::mem::size_of::<$ty>()];
     };
 }
+
+#[macro_export]
+#[cfg(feature = "rustc_randomized_layouts")]
+macro_rules! static_assert_size {
+    ($ty:ty, $size:expr) => {
+        // no effect other than using the statements.
+        // struct sizes are not deterministic under randomized layouts
+        const _: (usize, usize) = ($size, ::std::mem::size_of::<$ty>());
+    };
+}

compiler/rustc_index/src/lib.rs

@@ -40,5 +40,6 @@ tracing = "0.1"
 
 [features]
 # tidy-alphabetical-start
+rustc_randomized_layouts = []
 rustc_use_parallel_compiler = ["dep:rustc-rayon-core"]
 # tidy-alphabetical-end

compiler/rustc_middle/Cargo.toml

@@ -1307,6 +1307,9 @@ pub enum Rvalue<'tcx> {
     /// If the type of the place is an array, this is the array length. For slices (`[T]`, not
     /// `&[T]`) this accesses the place's metadata to determine the length. This rvalue is
     /// ill-formed for places of other types.
+    ///
+    /// This cannot be a `UnOp(PtrMetadata, _)` because that expects a value, and we only
+    /// have a place, and `UnOp(PtrMetadata, RawPtr(place))` is not a thing.
     Len(Place<'tcx>),
 
     /// Performs essentially all of the casts that can be performed via `as`.

compiler/rustc_middle/src/mir/syntax.rs

@@ -337,6 +337,7 @@ macro_rules! define_callbacks {
                 // Ensure that values grow no larger than 64 bytes by accident.
                 // Increase this limit if necessary, but do try to keep the size low if possible
                 #[cfg(target_pointer_width = "64")]
+                #[cfg(not(feature = "rustc_randomized_layouts"))]
                 const _: () = {
                     if mem::size_of::<Value<'static>>() > 64 {
                         panic!("{}", concat!(

compiler/rustc_middle/src/query/plumbing.rs

@@ -35,6 +35,7 @@ use rustc_data_structures::tagged_ptr::CopyTaggedPtr;
 use rustc_errors::{Diag, ErrorGuaranteed, StashKey};
 use rustc_hir::def::{CtorKind, CtorOf, DefKind, DocLinkResMap, LifetimeRes, Res};
 use rustc_hir::def_id::{CrateNum, DefId, DefIdMap, LocalDefId, LocalDefIdMap};
+use rustc_hir::LangItem;
 use rustc_index::IndexVec;
 use rustc_macros::{
     extension, Decodable, Encodable, HashStable, TyDecodable, TyEncodable, TypeFoldable,
@@ -1570,8 +1571,15 @@ impl<'tcx> TyCtxt<'tcx> {
             flags.insert(ReprFlags::RANDOMIZE_LAYOUT);
         }
 
+        // box is special, on the one hand the compiler assumes an ordered layout, with the pointer
+        // always at offset zero. On the other hand we want scalar abi optimizations.
+        let is_box = self.is_lang_item(did.to_def_id(), LangItem::OwnedBox);
+
         // This is here instead of layout because the choice must make it into metadata.
-        if !self.consider_optimizing(|| format!("Reorder fields of {:?}", self.def_path_str(did))) {
+        if is_box
+            || !self
+                .consider_optimizing(|| format!("Reorder fields of {:?}", self.def_path_str(did)))
+        {
             flags.insert(ReprFlags::IS_LINEAR);
         }
 

compiler/rustc_middle/src/ty/mod.rs

@@ -1695,6 +1695,8 @@ supported_targets! {
     ("armv7r-none-eabihf", armv7r_none_eabihf),
     ("armv8r-none-eabihf", armv8r_none_eabihf),
 
+    ("armv7-rtems-eabihf", armv7_rtems_eabihf),
+
     ("x86_64-pc-solaris", x86_64_pc_solaris),
     ("sparcv9-sun-solaris", sparcv9_sun_solaris),
 

compiler/rustc_target/src/spec/mod.rs

@@ -0,0 +1,35 @@
+use crate::spec::{cvs, Cc, LinkerFlavor, Lld, PanicStrategy, RelocModel, Target, TargetOptions};
+
+pub(crate) fn target() -> Target {
+    Target {
+        llvm_target: "armv7-unknown-none-eabihf".into(),
+        metadata: crate::spec::TargetMetadata {
+            description: Some("Armv7 RTEMS (Requires RTEMS toolchain and kernel".into()),
+            tier: Some(3),
+            host_tools: Some(false),
+            std: Some(true),
+        },
+        pointer_width: 32,
+        data_layout: "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64".into(),
+        arch: "arm".into(),
+
+        options: TargetOptions {
+            os: "rtems".into(),
+            families: cvs!["unix"],
+            abi: "eabihf".into(),
+            linker_flavor: LinkerFlavor::Gnu(Cc::Yes, Lld::No),
+            linker: None,
+            relocation_model: RelocModel::Static,
+            panic_strategy: PanicStrategy::Abort,
+            features: "+thumb2,+neon,+vfp3".into(),
+            max_atomic_width: Some(64),
+            emit_debug_gdb_scripts: false,
+            // GCC defaults to 8 for arm-none here.
+            c_enum_min_bits: Some(8),
+            eh_frame_header: false,
+            no_default_libraries: false,
+            env: "newlib".into(),
+            ..Default::default()
+        },
+    }
+}

compiler/rustc_target/src/spec/targets/armv7_rtems_eabihf.rs

@@ -237,7 +237,7 @@ pub fn supertrait_def_ids<I: Interner>(
     cx: I,
     trait_def_id: I::DefId,
 ) -> impl Iterator<Item = I::DefId> {
-    let mut set: HashSet<I::DefId> = HashSet::default();
+    let mut set = HashSet::default();
     let mut stack = vec![trait_def_id];
 
     set.insert(trait_def_id);

compiler/rustc_type_ir/src/elaborate.rs

@@ -519,6 +519,9 @@
 # are disabled statically" because `max_level_info` is enabled, set this value to `true`.
 #debug-logging = rust.debug-assertions (boolean)
 
+# Whether or not to build rustc, tools and the libraries with randomized type layout
+#randomize-layout = false
+
 # Whether or not overflow checks are enabled for the compiler and standard
 # library.
 #