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Align pointers to DST fields properly
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DST fields, being of an unknown type, are not automatically aligned
properly, so a pointer to the field needs to be aligned using the
information in the vtable.

Fixes #26403 and a number of other DST-related bugs discovered while
implementing this.
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@Aatch
Aatch committed Dec 7, 2015
1 parent 7b77f67 commit a2557d4
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Showing 11 changed files with 337 additions and 61 deletions.
72 changes: 57 additions & 15 deletions src/librustc_trans/trans/_match.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -709,8 +709,10 @@ fn extract_variant_args<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
val: MatchInput)
-> ExtractedBlock<'blk, 'tcx> {
let _icx = push_ctxt("match::extract_variant_args");
// Assume enums are always sized for now.
let val = adt::MaybeSizedValue::sized(val.val);
let args = (0..adt::num_args(repr, disr_val)).map(|i| {
adt::trans_field_ptr(bcx, repr, val.val, disr_val, i)
adt::trans_field_ptr(bcx, repr, val, disr_val, i)
}).collect();

ExtractedBlock { vals: args, bcx: bcx }
Expand Down Expand Up @@ -1199,7 +1201,8 @@ fn compile_submatch_continue<'a, 'p, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
(arg_count - 1, Load(bcx, expr::get_dataptr(bcx, val.val)))
};
let mut field_vals: Vec<ValueRef> = (0..arg_count).map(|ix|
adt::trans_field_ptr(bcx, &*repr, struct_val, 0, ix)
// By definition, these are all sized
adt::trans_field_ptr(bcx, &*repr, adt::MaybeSizedValue::sized(struct_val), 0, ix)
).collect();

match left_ty.sty {
Expand All @@ -1211,10 +1214,13 @@ fn compile_submatch_continue<'a, 'p, 'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
monomorphize::field_ty(bcx.tcx(), substs, field)
}).unwrap();
let scratch = alloc_ty(bcx, unsized_ty, "__struct_field_fat_ptr");

let meta = Load(bcx, expr::get_meta(bcx, val.val));
let struct_val = adt::MaybeSizedValue::unsized_(struct_val, meta);

let data = adt::trans_field_ptr(bcx, &*repr, struct_val, 0, arg_count);
let len = Load(bcx, expr::get_meta(bcx, val.val));
Store(bcx, data, expr::get_dataptr(bcx, scratch));
Store(bcx, len, expr::get_meta(bcx, scratch));
Store(bcx, meta, expr::get_meta(bcx, scratch));
field_vals.push(scratch);
}
_ => {}
Expand Down Expand Up @@ -1785,9 +1791,10 @@ pub fn bind_irrefutable_pat<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
val: MatchInput,
cleanup_scope: cleanup::ScopeId)
-> Block<'blk, 'tcx> {
debug!("bind_irrefutable_pat(bcx={}, pat={:?})",
debug!("bind_irrefutable_pat(bcx={}, pat={:?}, val={})",
bcx.to_str(),
pat);
pat,
bcx.val_to_string(val.val));

if bcx.sess().asm_comments() {
add_comment(bcx, &format!("bind_irrefutable_pat(pat={:?})",
Expand Down Expand Up @@ -1866,9 +1873,10 @@ pub fn bind_irrefutable_pat<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
Some(ref elems) => {
// This is the tuple struct case.
let repr = adt::represent_node(bcx, pat.id);
let val = adt::MaybeSizedValue::sized(val.val);
for (i, elem) in elems.iter().enumerate() {
let fldptr = adt::trans_field_ptr(bcx, &*repr,
val.val, 0, i);
val, 0, i);
bcx = bind_irrefutable_pat(
bcx,
&**elem,
Expand All @@ -1888,14 +1896,35 @@ pub fn bind_irrefutable_pat<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
let pat_ty = node_id_type(bcx, pat.id);
let pat_repr = adt::represent_type(bcx.ccx(), pat_ty);
let pat_v = VariantInfo::of_node(tcx, pat_ty, pat.id);

let val = if type_is_sized(tcx, pat_ty) {
adt::MaybeSizedValue::sized(val.val)
} else {
let data = Load(bcx, expr::get_dataptr(bcx, val.val));
let meta = Load(bcx, expr::get_meta(bcx, val.val));
adt::MaybeSizedValue::unsized_(data, meta)
};

for f in fields {
let name = f.node.name;
let fldptr = adt::trans_field_ptr(
let field_idx = pat_v.field_index(name);
let mut fldptr = adt::trans_field_ptr(
bcx,
&*pat_repr,
val.val,
val,
pat_v.discr,
pat_v.field_index(name));
field_idx);

let fty = pat_v.fields[field_idx].1;
// If it's not sized, then construct a fat pointer instead of
// a regular one
if !type_is_sized(tcx, fty) {
let scratch = alloc_ty(bcx, fty, "__struct_field_fat_ptr");
debug!("Creating fat pointer {}", bcx.val_to_string(scratch));
Store(bcx, fldptr, expr::get_dataptr(bcx, scratch));
Store(bcx, val.meta, expr::get_meta(bcx, scratch));
fldptr = scratch;
}
bcx = bind_irrefutable_pat(bcx,
&*f.node.pat,
MatchInput::from_val(fldptr),
Expand All @@ -1904,8 +1933,9 @@ pub fn bind_irrefutable_pat<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
}
hir::PatTup(ref elems) => {
let repr = adt::represent_node(bcx, pat.id);
let val = adt::MaybeSizedValue::sized(val.val);
for (i, elem) in elems.iter().enumerate() {
let fldptr = adt::trans_field_ptr(bcx, &*repr, val.val, 0, i);
let fldptr = adt::trans_field_ptr(bcx, &*repr, val, 0, i);
bcx = bind_irrefutable_pat(
bcx,
&**elem,
Expand All @@ -1914,16 +1944,28 @@ pub fn bind_irrefutable_pat<'blk, 'tcx>(bcx: Block<'blk, 'tcx>,
}
}
hir::PatBox(ref inner) => {
let llbox = Load(bcx, val.val);
let pat_ty = node_id_type(bcx, inner.id);
// Don't load DSTs, instead pass along a fat ptr
let val = if type_is_sized(tcx, pat_ty) {
Load(bcx, val.val)
} else {
val.val
};
bcx = bind_irrefutable_pat(
bcx, &**inner, MatchInput::from_val(llbox), cleanup_scope);
bcx, &**inner, MatchInput::from_val(val), cleanup_scope);
}
hir::PatRegion(ref inner, _) => {
let loaded_val = Load(bcx, val.val);
let pat_ty = node_id_type(bcx, inner.id);
// Don't load DSTs, instead pass along a fat ptr
let val = if type_is_sized(tcx, pat_ty) {
Load(bcx, val.val)
} else {
val.val
};
bcx = bind_irrefutable_pat(
bcx,
&**inner,
MatchInput::from_val(loaded_val),
MatchInput::from_val(val),
cleanup_scope);
}
hir::PatVec(ref before, ref slice, ref after) => {
Expand Down
127 changes: 116 additions & 11 deletions src/librustc_trans/trans/adt.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -43,6 +43,7 @@

pub use self::Repr::*;

use std;
use std::rc::Rc;

use llvm::{ValueRef, True, IntEQ, IntNE};
Expand All @@ -60,6 +61,7 @@ use trans::cleanup::CleanupMethods;
use trans::common::*;
use trans::datum;
use trans::debuginfo::DebugLoc;
use trans::glue;
use trans::machine;
use trans::monomorphize;
use trans::type_::Type;
Expand Down Expand Up @@ -153,6 +155,32 @@ pub struct Struct<'tcx> {
pub fields: Vec<Ty<'tcx>>,
}

#[derive(Copy, Clone)]
pub struct MaybeSizedValue {
pub value: ValueRef,
pub meta: ValueRef,
}

impl MaybeSizedValue {
pub fn sized(value: ValueRef) -> MaybeSizedValue {
MaybeSizedValue {
value: value,
meta: std::ptr::null_mut()
}
}

pub fn unsized_(value: ValueRef, meta: ValueRef) -> MaybeSizedValue {
MaybeSizedValue {
value: value,
meta: meta
}
}

pub fn has_meta(&self) -> bool {
!self.meta.is_null()
}
}

/// Convenience for `represent_type`. There should probably be more or
/// these, for places in trans where the `Ty` isn't directly
/// available.
Expand Down Expand Up @@ -976,7 +1004,7 @@ pub fn trans_set_discr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr<'tcx>,
}
General(ity, ref cases, dtor) => {
if dtor_active(dtor) {
let ptr = trans_field_ptr(bcx, r, val, discr,
let ptr = trans_field_ptr(bcx, r, MaybeSizedValue::sized(val), discr,
cases[discr as usize].fields.len() - 2);
Store(bcx, C_u8(bcx.ccx(), DTOR_NEEDED), ptr);
}
Expand Down Expand Up @@ -1037,7 +1065,7 @@ pub fn num_args(r: &Repr, discr: Disr) -> usize {

/// Access a field, at a point when the value's case is known.
pub fn trans_field_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr<'tcx>,
val: ValueRef, discr: Disr, ix: usize) -> ValueRef {
val: MaybeSizedValue, discr: Disr, ix: usize) -> ValueRef {
// Note: if this ever needs to generate conditionals (e.g., if we
// decide to do some kind of cdr-coding-like non-unique repr
// someday), it will need to return a possibly-new bcx as well.
Expand All @@ -1060,13 +1088,13 @@ pub fn trans_field_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr<'tcx>,
assert_eq!(machine::llsize_of_alloc(bcx.ccx(), ty), 0);
// The contents of memory at this pointer can't matter, but use
// the value that's "reasonable" in case of pointer comparison.
PointerCast(bcx, val, ty.ptr_to())
PointerCast(bcx, val.value, ty.ptr_to())
}
RawNullablePointer { nndiscr, nnty, .. } => {
assert_eq!(ix, 0);
assert_eq!(discr, nndiscr);
let ty = type_of::type_of(bcx.ccx(), nnty);
PointerCast(bcx, val, ty.ptr_to())
PointerCast(bcx, val.value, ty.ptr_to())
}
StructWrappedNullablePointer { ref nonnull, nndiscr, .. } => {
assert_eq!(discr, nndiscr);
Expand All @@ -1075,18 +1103,94 @@ pub fn trans_field_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, r: &Repr<'tcx>,
}
}

pub fn struct_field_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, st: &Struct<'tcx>, val: ValueRef,
pub fn struct_field_ptr<'blk, 'tcx>(bcx: Block<'blk, 'tcx>, st: &Struct<'tcx>, val: MaybeSizedValue,
ix: usize, needs_cast: bool) -> ValueRef {
let val = if needs_cast {
let ptr_val = if needs_cast {
let ccx = bcx.ccx();
let fields = st.fields.iter().map(|&ty| type_of::type_of(ccx, ty)).collect::<Vec<_>>();
let fields = st.fields.iter().map(|&ty| {
type_of::in_memory_type_of(ccx, ty)
}).collect::<Vec<_>>();
let real_ty = Type::struct_(ccx, &fields[..], st.packed);
PointerCast(bcx, val, real_ty.ptr_to())
PointerCast(bcx, val.value, real_ty.ptr_to())
} else {
val
val.value
};

StructGEP(bcx, val, ix)
let fty = st.fields[ix];
// Simple case - we can just GEP the field
// * First field - Always aligned properly
// * Packed struct - There is no alignment padding
// * Field is sized - pointer is properly aligned already
if ix == 0 || st.packed || type_is_sized(bcx.tcx(), fty) {
return StructGEP(bcx, ptr_val, ix);
}

// If the type of the last field is [T] or str, then we don't need to do
// any adjusments
match fty.sty {
ty::TySlice(..) | ty::TyStr => {
return StructGEP(bcx, ptr_val, ix);
}
_ => ()
}

// There's no metadata available, log the case and just do the GEP.
if !val.has_meta() {
debug!("Unsized field `{}`, of `{}` has no metadata for adjustment",
ix,
bcx.val_to_string(ptr_val));
return StructGEP(bcx, ptr_val, ix);
}

let dbloc = DebugLoc::None;

// We need to get the pointer manually now.
// We do this by casting to a *i8, then offsetting it by the appropriate amount.
// We do this instead of, say, simply adjusting the pointer from the result of a GEP
// because the the field may have an arbitrary alignment in the LLVM representation
// anyway.
//
// To demonstrate:
// struct Foo<T: ?Sized> {
// x: u16,
// y: T
// }
//
// The type Foo<Foo<Trait>> is represented in LLVM as { u16, { u16, u8 }}, meaning that
// the `y` field has 16-bit alignment.

let meta = val.meta;

// st.size is the size of the sized portion of the struct. So the position
// exactly after it is the offset for unaligned data.
let unaligned_offset = C_uint(bcx.ccx(), st.size);

// Get the alignment of the field
let (_, align) = glue::size_and_align_of_dst(bcx, fty, meta);

// Bump the unaligned offset up to the appropriate alignment using the
// following expression:
//
// (unaligned offset + (align - 1)) & -align

// Calculate offset
let align_sub_1 = Sub(bcx, align, C_uint(bcx.ccx(), 1u64), dbloc);
let offset = And(bcx,
Add(bcx, unaligned_offset, align_sub_1, dbloc),
Neg(bcx, align, dbloc),
dbloc);

debug!("struct_field_ptr: DST field offset: {}",
bcx.val_to_string(offset));

// Cast and adjust pointer
let byte_ptr = PointerCast(bcx, ptr_val, Type::i8p(bcx.ccx()));
let byte_ptr = GEP(bcx, byte_ptr, &[offset]);

// Finally, cast back to the type expected
let ll_fty = type_of::in_memory_type_of(bcx.ccx(), fty);
debug!("struct_field_ptr: Field type is {}", ll_fty.to_string());
PointerCast(bcx, byte_ptr, ll_fty.ptr_to())
}

pub fn fold_variants<'blk, 'tcx, F>(bcx: Block<'blk, 'tcx>,
Expand Down Expand Up @@ -1168,7 +1272,8 @@ pub fn trans_drop_flag_ptr<'blk, 'tcx>(mut bcx: Block<'blk, 'tcx>,
cleanup::CustomScope(custom_cleanup_scope), (), |_, bcx, _| bcx
));
bcx = fold_variants(bcx, r, val, |variant_cx, st, value| {
let ptr = struct_field_ptr(variant_cx, st, value, (st.fields.len() - 1), false);
let ptr = struct_field_ptr(variant_cx, st, MaybeSizedValue::sized(value),
(st.fields.len() - 1), false);
datum::Datum::new(ptr, ptr_ty, datum::Lvalue::new("adt::trans_drop_flag_ptr"))
.store_to(variant_cx, scratch.val)
});
Expand Down
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