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Rollup merge of #63448 - RalfJung:miri-discriminant, r=eddyb
fix Miri discriminant handling This can be reviewed commit-by-commit fairly well. The Miri side is at rust-lang/miri#903. Fixes #62138 r? @eddyb @oli-obk
2 parents 9b9d2af + 1de533a commit bda52e5

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5 files changed

+253
-27
lines changed

5 files changed

+253
-27
lines changed

‎src/librustc/ty/layout.rs

+11
Original file line numberDiff line numberDiff line change
@@ -127,6 +127,7 @@ impl IntegerExt for Integer {
127127

128128
pub trait PrimitiveExt {
129129
fn to_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
130+
fn to_int_ty<'tcx>(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx>;
130131
}
131132

132133
impl PrimitiveExt for Primitive {
@@ -138,6 +139,16 @@ impl PrimitiveExt for Primitive {
138139
Pointer => tcx.mk_mut_ptr(tcx.mk_unit()),
139140
}
140141
}
142+
143+
/// Return an *integer* type matching this primitive.
144+
/// Useful in particular when dealing with enum discriminants.
145+
fn to_int_ty(&self, tcx: TyCtxt<'tcx>) -> Ty<'tcx> {
146+
match *self {
147+
Int(i, signed) => i.to_ty(tcx, signed),
148+
Pointer => tcx.types.usize,
149+
Float(..) => bug!("floats do not have an int type"),
150+
}
151+
}
141152
}
142153

143154
/// The first half of a fat pointer.

‎src/librustc_mir/interpret/operand.rs

+37-16
Original file line numberDiff line numberDiff line change
@@ -1,11 +1,11 @@
11
//! Functions concerning immediate values and operands, and reading from operands.
22
//! All high-level functions to read from memory work on operands as sources.
33
4-
use std::convert::TryInto;
4+
use std::convert::{TryInto, TryFrom};
55

66
use rustc::{mir, ty};
77
use rustc::ty::layout::{
8-
self, Size, LayoutOf, TyLayout, HasDataLayout, IntegerExt, VariantIdx,
8+
self, Size, LayoutOf, TyLayout, HasDataLayout, IntegerExt, PrimitiveExt, VariantIdx,
99
};
1010

1111
use rustc::mir::interpret::{
@@ -609,15 +609,20 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
609609
) -> InterpResult<'tcx, (u128, VariantIdx)> {
610610
trace!("read_discriminant_value {:#?}", rval.layout);
611611

612-
let (discr_kind, discr_index) = match rval.layout.variants {
612+
let (discr_layout, discr_kind, discr_index) = match rval.layout.variants {
613613
layout::Variants::Single { index } => {
614614
let discr_val = rval.layout.ty.discriminant_for_variant(*self.tcx, index).map_or(
615615
index.as_u32() as u128,
616616
|discr| discr.val);
617617
return Ok((discr_val, index));
618618
}
619-
layout::Variants::Multiple { ref discr_kind, discr_index, .. } =>
620-
(discr_kind, discr_index),
619+
layout::Variants::Multiple {
620+
discr: ref discr_layout,
621+
ref discr_kind,
622+
discr_index,
623+
..
624+
} =>
625+
(discr_layout, discr_kind, discr_index),
621626
};
622627

623628
// read raw discriminant value
@@ -634,7 +639,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
634639
.map_err(|_| err_unsup!(InvalidDiscriminant(raw_discr.erase_tag())))?;
635640
let real_discr = if discr_val.layout.ty.is_signed() {
636641
// going from layout tag type to typeck discriminant type
637-
// requires first sign extending with the layout discriminant
642+
// requires first sign extending with the discriminant layout
638643
let sexted = sign_extend(bits_discr, discr_val.layout.size) as i128;
639644
// and then zeroing with the typeck discriminant type
640645
let discr_ty = rval.layout.ty
@@ -666,8 +671,8 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
666671
ref niche_variants,
667672
niche_start,
668673
} => {
669-
let variants_start = niche_variants.start().as_u32() as u128;
670-
let variants_end = niche_variants.end().as_u32() as u128;
674+
let variants_start = niche_variants.start().as_u32();
675+
let variants_end = niche_variants.end().as_u32();
671676
let raw_discr = raw_discr.not_undef().map_err(|_| {
672677
err_unsup!(InvalidDiscriminant(ScalarMaybeUndef::Undef))
673678
})?;
@@ -682,18 +687,34 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
682687
(dataful_variant.as_u32() as u128, dataful_variant)
683688
},
684689
Ok(raw_discr) => {
685-
let adjusted_discr = raw_discr.wrapping_sub(niche_start)
686-
.wrapping_add(variants_start);
687-
if variants_start <= adjusted_discr && adjusted_discr <= variants_end {
688-
let index = adjusted_discr as usize;
689-
assert_eq!(index as u128, adjusted_discr);
690-
assert!(index < rval.layout.ty
690+
// We need to use machine arithmetic to get the relative variant idx:
691+
// variant_index_relative = discr_val - niche_start_val
692+
let discr_layout = self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
693+
let discr_val = ImmTy::from_uint(raw_discr, discr_layout);
694+
let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
695+
let variant_index_relative_val = self.binary_op(
696+
mir::BinOp::Sub,
697+
discr_val,
698+
niche_start_val,
699+
)?;
700+
let variant_index_relative = variant_index_relative_val
701+
.to_scalar()?
702+
.assert_bits(discr_val.layout.size);
703+
// Check if this is in the range that indicates an actual discriminant.
704+
if variant_index_relative <= u128::from(variants_end - variants_start) {
705+
let variant_index_relative = u32::try_from(variant_index_relative)
706+
.expect("we checked that this fits into a u32");
707+
// Then computing the absolute variant idx should not overflow any more.
708+
let variant_index = variants_start
709+
.checked_add(variant_index_relative)
710+
.expect("oveflow computing absolute variant idx");
711+
assert!((variant_index as usize) < rval.layout.ty
691712
.ty_adt_def()
692713
.expect("tagged layout for non adt")
693714
.variants.len());
694-
(adjusted_discr, VariantIdx::from_usize(index))
715+
(u128::from(variant_index), VariantIdx::from_u32(variant_index))
695716
} else {
696-
(dataful_variant.as_u32() as u128, dataful_variant)
717+
(u128::from(dataful_variant.as_u32()), dataful_variant)
697718
}
698719
},
699720
}

‎src/librustc_mir/interpret/place.rs

+23-11
Original file line numberDiff line numberDiff line change
@@ -8,7 +8,9 @@ use std::hash::Hash;
88
use rustc::mir;
99
use rustc::mir::interpret::truncate;
1010
use rustc::ty::{self, Ty};
11-
use rustc::ty::layout::{self, Size, Align, LayoutOf, TyLayout, HasDataLayout, VariantIdx};
11+
use rustc::ty::layout::{
12+
self, Size, Align, LayoutOf, TyLayout, HasDataLayout, VariantIdx, PrimitiveExt
13+
};
1214
use rustc::ty::TypeFoldable;
1315

1416
use super::{
@@ -1027,7 +1029,7 @@ where
10271029
}
10281030
layout::Variants::Multiple {
10291031
discr_kind: layout::DiscriminantKind::Tag,
1030-
ref discr,
1032+
discr: ref discr_layout,
10311033
discr_index,
10321034
..
10331035
} => {
@@ -1038,7 +1040,7 @@ where
10381040
// raw discriminants for enums are isize or bigger during
10391041
// their computation, but the in-memory tag is the smallest possible
10401042
// representation
1041-
let size = discr.value.size(self);
1043+
let size = discr_layout.value.size(self);
10421044
let discr_val = truncate(discr_val, size);
10431045

10441046
let discr_dest = self.place_field(dest, discr_index as u64)?;
@@ -1050,22 +1052,32 @@ where
10501052
ref niche_variants,
10511053
niche_start,
10521054
},
1055+
discr: ref discr_layout,
10531056
discr_index,
10541057
..
10551058
} => {
10561059
assert!(
10571060
variant_index.as_usize() < dest.layout.ty.ty_adt_def().unwrap().variants.len(),
10581061
);
10591062
if variant_index != dataful_variant {
1060-
let niche_dest =
1061-
self.place_field(dest, discr_index as u64)?;
1062-
let niche_value = variant_index.as_u32() - niche_variants.start().as_u32();
1063-
let niche_value = (niche_value as u128)
1064-
.wrapping_add(niche_start);
1065-
self.write_scalar(
1066-
Scalar::from_uint(niche_value, niche_dest.layout.size),
1067-
niche_dest
1063+
let variants_start = niche_variants.start().as_u32();
1064+
let variant_index_relative = variant_index.as_u32()
1065+
.checked_sub(variants_start)
1066+
.expect("overflow computing relative variant idx");
1067+
// We need to use machine arithmetic when taking into account `niche_start`:
1068+
// discr_val = variant_index_relative + niche_start_val
1069+
let discr_layout = self.layout_of(discr_layout.value.to_int_ty(*self.tcx))?;
1070+
let niche_start_val = ImmTy::from_uint(niche_start, discr_layout);
1071+
let variant_index_relative_val =
1072+
ImmTy::from_uint(variant_index_relative, discr_layout);
1073+
let discr_val = self.binary_op(
1074+
mir::BinOp::Add,
1075+
variant_index_relative_val,
1076+
niche_start_val,
10681077
)?;
1078+
// Write result.
1079+
let niche_dest = self.place_field(dest, discr_index as u64)?;
1080+
self.write_immediate(*discr_val, niche_dest)?;
10691081
}
10701082
}
10711083
}

‎src/test/ui/consts/miri_unleashed/enum_discriminants.rs

+110
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,110 @@
1+
// compile-flags: -Zunleash-the-miri-inside-of-you
2+
// run-pass
3+
4+
//! Make sure that we read and write enum discriminants correctly for corner cases caused
5+
//! by layout optimizations.
6+
7+
const OVERFLOW: usize = {
8+
// Tests for https://github.com/rust-lang/rust/issues/62138.
9+
#[repr(u8)]
10+
#[allow(dead_code)]
11+
enum WithWraparoundInvalidValues {
12+
X = 1,
13+
Y = 254,
14+
}
15+
16+
#[allow(dead_code)]
17+
enum Foo {
18+
A,
19+
B,
20+
C(WithWraparoundInvalidValues),
21+
}
22+
23+
let x = Foo::B;
24+
match x {
25+
Foo::B => 0,
26+
_ => panic!(),
27+
}
28+
};
29+
30+
const MORE_OVERFLOW: usize = {
31+
pub enum Infallible {}
32+
33+
// The check that the `bool` field of `V1` is encoding a "niche variant"
34+
// (i.e. not `V1`, so `V3` or `V4`) used to be mathematically incorrect,
35+
// causing valid `V1` values to be interpreted as other variants.
36+
#[allow(dead_code)]
37+
pub enum E1 {
38+
V1 { f: bool },
39+
V2 { f: Infallible },
40+
V3,
41+
V4,
42+
}
43+
44+
// Computing the discriminant used to be done using the niche type (here `u8`,
45+
// from the `bool` field of `V1`), overflowing for variants with large enough
46+
// indices (`V3` and `V4`), causing them to be interpreted as other variants.
47+
#[allow(dead_code)]
48+
pub enum E2<X> {
49+
V1 { f: bool },
50+
51+
/*_00*/ _01(X), _02(X), _03(X), _04(X), _05(X), _06(X), _07(X),
52+
_08(X), _09(X), _0A(X), _0B(X), _0C(X), _0D(X), _0E(X), _0F(X),
53+
_10(X), _11(X), _12(X), _13(X), _14(X), _15(X), _16(X), _17(X),
54+
_18(X), _19(X), _1A(X), _1B(X), _1C(X), _1D(X), _1E(X), _1F(X),
55+
_20(X), _21(X), _22(X), _23(X), _24(X), _25(X), _26(X), _27(X),
56+
_28(X), _29(X), _2A(X), _2B(X), _2C(X), _2D(X), _2E(X), _2F(X),
57+
_30(X), _31(X), _32(X), _33(X), _34(X), _35(X), _36(X), _37(X),
58+
_38(X), _39(X), _3A(X), _3B(X), _3C(X), _3D(X), _3E(X), _3F(X),
59+
_40(X), _41(X), _42(X), _43(X), _44(X), _45(X), _46(X), _47(X),
60+
_48(X), _49(X), _4A(X), _4B(X), _4C(X), _4D(X), _4E(X), _4F(X),
61+
_50(X), _51(X), _52(X), _53(X), _54(X), _55(X), _56(X), _57(X),
62+
_58(X), _59(X), _5A(X), _5B(X), _5C(X), _5D(X), _5E(X), _5F(X),
63+
_60(X), _61(X), _62(X), _63(X), _64(X), _65(X), _66(X), _67(X),
64+
_68(X), _69(X), _6A(X), _6B(X), _6C(X), _6D(X), _6E(X), _6F(X),
65+
_70(X), _71(X), _72(X), _73(X), _74(X), _75(X), _76(X), _77(X),
66+
_78(X), _79(X), _7A(X), _7B(X), _7C(X), _7D(X), _7E(X), _7F(X),
67+
_80(X), _81(X), _82(X), _83(X), _84(X), _85(X), _86(X), _87(X),
68+
_88(X), _89(X), _8A(X), _8B(X), _8C(X), _8D(X), _8E(X), _8F(X),
69+
_90(X), _91(X), _92(X), _93(X), _94(X), _95(X), _96(X), _97(X),
70+
_98(X), _99(X), _9A(X), _9B(X), _9C(X), _9D(X), _9E(X), _9F(X),
71+
_A0(X), _A1(X), _A2(X), _A3(X), _A4(X), _A5(X), _A6(X), _A7(X),
72+
_A8(X), _A9(X), _AA(X), _AB(X), _AC(X), _AD(X), _AE(X), _AF(X),
73+
_B0(X), _B1(X), _B2(X), _B3(X), _B4(X), _B5(X), _B6(X), _B7(X),
74+
_B8(X), _B9(X), _BA(X), _BB(X), _BC(X), _BD(X), _BE(X), _BF(X),
75+
_C0(X), _C1(X), _C2(X), _C3(X), _C4(X), _C5(X), _C6(X), _C7(X),
76+
_C8(X), _C9(X), _CA(X), _CB(X), _CC(X), _CD(X), _CE(X), _CF(X),
77+
_D0(X), _D1(X), _D2(X), _D3(X), _D4(X), _D5(X), _D6(X), _D7(X),
78+
_D8(X), _D9(X), _DA(X), _DB(X), _DC(X), _DD(X), _DE(X), _DF(X),
79+
_E0(X), _E1(X), _E2(X), _E3(X), _E4(X), _E5(X), _E6(X), _E7(X),
80+
_E8(X), _E9(X), _EA(X), _EB(X), _EC(X), _ED(X), _EE(X), _EF(X),
81+
_F0(X), _F1(X), _F2(X), _F3(X), _F4(X), _F5(X), _F6(X), _F7(X),
82+
_F8(X), _F9(X), _FA(X), _FB(X), _FC(X), _FD(X), _FE(X), _FF(X),
83+
84+
V3,
85+
V4,
86+
}
87+
88+
if let E1::V2 { .. } = (E1::V1 { f: true }) {
89+
unreachable!()
90+
}
91+
if let E1::V1 { .. } = (E1::V1 { f: true }) {
92+
} else {
93+
unreachable!()
94+
}
95+
96+
if let E2::V1 { .. } = E2::V3::<Infallible> {
97+
unreachable!()
98+
}
99+
if let E2::V3 { .. } = E2::V3::<Infallible> {
100+
} else {
101+
unreachable!()
102+
}
103+
104+
0
105+
};
106+
107+
fn main() {
108+
assert_eq!(OVERFLOW, 0);
109+
assert_eq!(MORE_OVERFLOW, 0);
110+
}

‎src/test/ui/consts/miri_unleashed/enum_discriminants.stderr

+72
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,72 @@
1+
warning: skipping const checks
2+
--> $DIR/enum_discriminants.rs:23:13
3+
|
4+
LL | let x = Foo::B;
5+
| ^^^^^^
6+
7+
warning: skipping const checks
8+
--> $DIR/enum_discriminants.rs:25:9
9+
|
10+
LL | Foo::B => 0,
11+
| ^^^^^^
12+
13+
warning: skipping const checks
14+
--> $DIR/enum_discriminants.rs:88:28
15+
|
16+
LL | if let E1::V2 { .. } = (E1::V1 { f: true }) {
17+
| ^^^^^^^^^^^^^^^^^^^^
18+
19+
warning: skipping const checks
20+
--> $DIR/enum_discriminants.rs:88:12
21+
|
22+
LL | if let E1::V2 { .. } = (E1::V1 { f: true }) {
23+
| ^^^^^^^^^^^^^
24+
25+
warning: skipping const checks
26+
--> $DIR/enum_discriminants.rs:108:5
27+
|
28+
LL | assert_eq!(OVERFLOW, 0);
29+
| ^^^^^^^^^^^^^^^^^^^^^^^^
30+
|
31+
= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
32+
33+
warning: skipping const checks
34+
--> $DIR/enum_discriminants.rs:108:5
35+
|
36+
LL | assert_eq!(OVERFLOW, 0);
37+
| ^^^^^^^^^^^^^^^^^^^^^^^^
38+
|
39+
= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
40+
41+
warning: skipping const checks
42+
--> $DIR/enum_discriminants.rs:108:5
43+
|
44+
LL | assert_eq!(OVERFLOW, 0);
45+
| ^^^^^^^^^^^^^^^^^^^^^^^^
46+
|
47+
= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
48+
49+
warning: skipping const checks
50+
--> $DIR/enum_discriminants.rs:109:5
51+
|
52+
LL | assert_eq!(MORE_OVERFLOW, 0);
53+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
54+
|
55+
= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
56+
57+
warning: skipping const checks
58+
--> $DIR/enum_discriminants.rs:109:5
59+
|
60+
LL | assert_eq!(MORE_OVERFLOW, 0);
61+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
62+
|
63+
= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
64+
65+
warning: skipping const checks
66+
--> $DIR/enum_discriminants.rs:109:5
67+
|
68+
LL | assert_eq!(MORE_OVERFLOW, 0);
69+
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
70+
|
71+
= note: this warning originates in a macro outside of the current crate (in Nightly builds, run with -Z external-macro-backtrace for more info)
72+

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