diff options
| -rw-r--r-- | compiler/rustc_codegen_ssa/src/size_of_val.rs | 62 | ||||
| -rw-r--r-- | compiler/rustc_const_eval/src/interpret/eval_context.rs | 43 | ||||
| -rw-r--r-- | src/tools/miri/tests/pass/packed-struct-dyn-trait.rs | 21 | ||||
| -rw-r--r-- | tests/ui/packed/dyn-trait.rs | 21 |
4 files changed, 99 insertions, 48 deletions
diff --git a/compiler/rustc_codegen_ssa/src/size_of_val.rs b/compiler/rustc_codegen_ssa/src/size_of_val.rs index b8a4949d59f..087836ca37d 100644 --- a/compiler/rustc_codegen_ssa/src/size_of_val.rs +++ b/compiler/rustc_codegen_ssa/src/size_of_val.rs @@ -84,10 +84,13 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( debug!("DST {} layout: {:?}", t, layout); let i = layout.fields.count() - 1; - let sized_size = layout.fields.offset(i).bytes(); + let unsized_offset_unadjusted = layout.fields.offset(i).bytes(); let sized_align = layout.align.abi.bytes(); - debug!("DST {} statically sized prefix size: {} align: {}", t, sized_size, sized_align); - let sized_size = bx.const_usize(sized_size); + debug!( + "DST {} offset of dyn field: {}, statically sized align: {}", + t, unsized_offset_unadjusted, sized_align + ); + let unsized_offset_unadjusted = bx.const_usize(unsized_offset_unadjusted); let sized_align = bx.const_usize(sized_align); // Recurse to get the size of the dynamically sized field (must be @@ -95,26 +98,26 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( let field_ty = layout.field(bx, i).ty; let (unsized_size, mut unsized_align) = size_and_align_of_dst(bx, field_ty, info); - // FIXME (#26403, #27023): We should be adding padding - // to `sized_size` (to accommodate the `unsized_align` - // required of the unsized field that follows) before - // summing it with `sized_size`. (Note that since #26403 - // is unfixed, we do not yet add the necessary padding - // here. But this is where the add would go.) - - // Return the sum of sizes and max of aligns. - let size = bx.add(sized_size, unsized_size); - - // Packed types ignore the alignment of their fields. - if let ty::Adt(def, _) = t.kind() { - if def.repr().packed() { - unsized_align = sized_align; + // # First compute the dynamic alignment + + // For packed types, we need to cap the alignment. + if let ty::Adt(def, _) = t.kind() + && let Some(packed) = def.repr().pack + { + if packed.bytes() == 1 { + // We know this will be capped to 1. + unsized_align = bx.const_usize(1); + } else { + // We have to dynamically compute `min(unsized_align, packed)`. + let packed = bx.const_usize(packed.bytes()); + let cmp = bx.icmp(IntPredicate::IntULT, unsized_align, packed); + unsized_align = bx.select(cmp, unsized_align, packed); } } // Choose max of two known alignments (combined value must // be aligned according to more restrictive of the two). - let align = match ( + let full_align = match ( bx.const_to_opt_u128(sized_align, false), bx.const_to_opt_u128(unsized_align, false), ) { @@ -129,6 +132,19 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( } }; + // # Then compute the dynamic size + + // The full formula for the size would be: + // let unsized_offset_adjusted = unsized_offset_unadjusted.align_to(unsized_align); + // let full_size = (unsized_offset_adjusted + unsized_size).align_to(full_align); + // However, `unsized_size` is a multiple of `unsized_align`. + // Therefore, we can equivalently do the `align_to(unsized_align)` *after* adding `unsized_size`: + // let full_size = (unsized_offset_unadjusted + unsized_size).align_to(unsized_align).align_to(full_align); + // Furthermore, `align >= unsized_align`, and therefore we only need to do: + // let full_size = (unsized_offset_unadjusted + unsized_size).align_to(full_align); + + let full_size = bx.add(unsized_offset_unadjusted, unsized_size); + // Issue #27023: must add any necessary padding to `size` // (to make it a multiple of `align`) before returning it. // @@ -140,12 +156,12 @@ pub fn size_and_align_of_dst<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>( // // `(size + (align-1)) & -align` let one = bx.const_usize(1); - let addend = bx.sub(align, one); - let add = bx.add(size, addend); - let neg = bx.neg(align); - let size = bx.and(add, neg); + let addend = bx.sub(full_align, one); + let add = bx.add(full_size, addend); + let neg = bx.neg(full_align); + let full_size = bx.and(add, neg); - (size, align) + (full_size, full_align) } _ => bug!("size_and_align_of_dst: {t} not supported"), } diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs index bbebf329d26..847d6503f20 100644 --- a/compiler/rustc_const_eval/src/interpret/eval_context.rs +++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs @@ -686,14 +686,8 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { assert!(layout.fields.count() > 0); trace!("DST layout: {:?}", layout); - let sized_size = layout.fields.offset(layout.fields.count() - 1); + let unsized_offset_unadjusted = layout.fields.offset(layout.fields.count() - 1); let sized_align = layout.align.abi; - trace!( - "DST {} statically sized prefix size: {:?} align: {:?}", - layout.ty, - sized_size, - sized_align - ); // Recurse to get the size of the dynamically sized field (must be // the last field). Can't have foreign types here, how would we @@ -707,36 +701,35 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> { return Ok(None); }; - // FIXME (#26403, #27023): We should be adding padding - // to `sized_size` (to accommodate the `unsized_align` - // required of the unsized field that follows) before - // summing it with `sized_size`. (Note that since #26403 - // is unfixed, we do not yet add the necessary padding - // here. But this is where the add would go.) - - // Return the sum of sizes and max of aligns. - let size = sized_size + unsized_size; // `Size` addition + // # First compute the dynamic alignment - // Packed types ignore the alignment of their fields. + // Packed type alignment needs to be capped. if let ty::Adt(def, _) = layout.ty.kind() { - if def.repr().packed() { - unsized_align = sized_align; + if let Some(packed) = def.repr().pack { + unsized_align = unsized_align.min(packed); } } // Choose max of two known alignments (combined value must // be aligned according to more restrictive of the two). - let align = sized_align.max(unsized_align); + let full_align = sized_align.max(unsized_align); + + // # Then compute the dynamic size - // Issue #27023: must add any necessary padding to `size` - // (to make it a multiple of `align`) before returning it. - let size = size.align_to(align); + let unsized_offset_adjusted = unsized_offset_unadjusted.align_to(unsized_align); + let full_size = (unsized_offset_adjusted + unsized_size).align_to(full_align); + + // Just for our sanitiy's sake, assert that this is equal to what codegen would compute. + assert_eq!( + full_size, + (unsized_offset_unadjusted + unsized_size).align_to(full_align) + ); // Check if this brought us over the size limit. - if size > self.max_size_of_val() { + if full_size > self.max_size_of_val() { throw_ub!(InvalidMeta(InvalidMetaKind::TooBig)); } - Ok(Some((size, align))) + Ok(Some((full_size, full_align))) } ty::Dynamic(_, _, ty::Dyn) => { let vtable = metadata.unwrap_meta().to_pointer(self)?; diff --git a/src/tools/miri/tests/pass/packed-struct-dyn-trait.rs b/src/tools/miri/tests/pass/packed-struct-dyn-trait.rs new file mode 100644 index 00000000000..bb73c26c18a --- /dev/null +++ b/src/tools/miri/tests/pass/packed-struct-dyn-trait.rs @@ -0,0 +1,21 @@ +// run-pass +use std::ptr::addr_of; + +// When the unsized tail is a `dyn Trait`, its alignments is only dynamically known. This means the +// packed(2) needs to be applied at runtime: the actual alignment of the field is `min(2, +// usual_alignment)`. Here we check that we do this right by comparing size, alignment, and field +// offset before and after unsizing. +fn main() { + #[repr(C, packed(2))] + struct Packed<T: ?Sized>(u8, core::mem::ManuallyDrop<T>); + + let p = Packed(0, core::mem::ManuallyDrop::new(1)); + let p: &Packed<usize> = &p; + let sized = (core::mem::size_of_val(p), core::mem::align_of_val(p)); + let sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) }; + let p: &Packed<dyn Send> = p; + let un_sized = (core::mem::size_of_val(p), core::mem::align_of_val(p)); + let un_sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) }; + assert_eq!(sized, un_sized); + assert_eq!(sized_offset, un_sized_offset); +} diff --git a/tests/ui/packed/dyn-trait.rs b/tests/ui/packed/dyn-trait.rs new file mode 100644 index 00000000000..bb73c26c18a --- /dev/null +++ b/tests/ui/packed/dyn-trait.rs @@ -0,0 +1,21 @@ +// run-pass +use std::ptr::addr_of; + +// When the unsized tail is a `dyn Trait`, its alignments is only dynamically known. This means the +// packed(2) needs to be applied at runtime: the actual alignment of the field is `min(2, +// usual_alignment)`. Here we check that we do this right by comparing size, alignment, and field +// offset before and after unsizing. +fn main() { + #[repr(C, packed(2))] + struct Packed<T: ?Sized>(u8, core::mem::ManuallyDrop<T>); + + let p = Packed(0, core::mem::ManuallyDrop::new(1)); + let p: &Packed<usize> = &p; + let sized = (core::mem::size_of_val(p), core::mem::align_of_val(p)); + let sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) }; + let p: &Packed<dyn Send> = p; + let un_sized = (core::mem::size_of_val(p), core::mem::align_of_val(p)); + let un_sized_offset = unsafe { addr_of!(p.1).cast::<u8>().offset_from(addr_of!(p.0)) }; + assert_eq!(sized, un_sized); + assert_eq!(sized_offset, un_sized_offset); +} |