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Implemented -Z randomize-layout

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Chase Wilson 2021-08-29 08:55:29 -07:00
parent 6dc08b909b
commit 09f1542418
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GPG key ID: 65D05E5367092801
6 changed files with 93 additions and 19 deletions
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48
compiler/rustc_middle/src/ty/layout.rs
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@ -24,6 +24,9 @@ use std::iter;
use std::num::NonZeroUsize;
use std::ops::Bound;
use rand::{seq::SliceRandom, SeedableRng};
use rand_xoshiro::Xoshiro128StarStar;
pub fn provide(providers: &mut ty::query::Providers) {
*providers =
ty::query::Providers { layout_of, fn_abi_of_fn_ptr, fn_abi_of_instance, ..*providers };
@ -324,6 +327,10 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let mut inverse_memory_index: Vec<u32> = (0..fields.len() as u32).collect();
// `ReprOptions.layout_seed` is a deterministic seed that we can use to
// randomize field ordering with
let mut rng = Xoshiro128StarStar::seed_from_u64(repr.field_shuffle_seed);
let optimize = !repr.inhibit_struct_field_reordering_opt();
if optimize {
let end =
@ -332,20 +339,35 @@ impl<'tcx> LayoutCx<'tcx, TyCtxt<'tcx>> {
let field_align = |f: &TyAndLayout<'_>| {
if let Some(pack) = pack { f.align.abi.min(pack) } else { f.align.abi }
};
match kind {
StructKind::AlwaysSized | StructKind::MaybeUnsized => {
optimizing.sort_by_key(|&x| {
// Place ZSTs first to avoid "interesting offsets",
// especially with only one or two non-ZST fields.
let f = &fields[x as usize];
(!f.is_zst(), cmp::Reverse(field_align(f)))
});
}
StructKind::Prefixed(..) => {
// Sort in ascending alignment so that the layout stay optimal
// regardless of the prefix
optimizing.sort_by_key(|&x| field_align(&fields[x as usize]));
// If `-Z randomize-layout` was enabled for the type definition we can shuffle
// the field ordering to try and catch some code making assumptions about layouts
// we don't guarantee
if repr.can_randomize_type_layout() {
// Shuffle the ordering of the fields
optimizing.shuffle(&mut rng);
// Otherwise we just leave things alone and actually optimize the type's fields
} else {
match kind {
StructKind::AlwaysSized | StructKind::MaybeUnsized => {
optimizing.sort_by_key(|&x| {
// Place ZSTs first to avoid "interesting offsets",
// especially with only one or two non-ZST fields.
let f = &fields[x as usize];
(!f.is_zst(), cmp::Reverse(field_align(f)))
});
}
StructKind::Prefixed(..) => {
// Sort in ascending alignment so that the layout stays optimal
// regardless of the prefix
optimizing.sort_by_key(|&x| field_align(&fields[x as usize]));
}
}
// FIXME(Kixiron): We can always shuffle fields within a given alignment class
// regardless of the status of `-Z randomize-layout`
}
}