From ee1caae33c9082c44387b2dc9b939db9f764a8f3 Mon Sep 17 00:00:00 2001 From: Ralf Jung Date: Sun, 28 Mar 2021 12:50:20 +0200 Subject: [PATCH] unaligned_references: align(N) fields in packed(N) structs are fine --- compiler/rustc_mir/src/util/alignment.rs | 35 ++++++++++++++------ src/test/ui/lint/unaligned_references.rs | 15 +++++++++ src/test/ui/lint/unaligned_references.stderr | 24 ++++++++++---- 3 files changed, 56 insertions(+), 18 deletions(-) diff --git a/compiler/rustc_mir/src/util/alignment.rs b/compiler/rustc_mir/src/util/alignment.rs index f567c9cfaab..5d4ca871faa 100644 --- a/compiler/rustc_mir/src/util/alignment.rs +++ b/compiler/rustc_mir/src/util/alignment.rs @@ -1,5 +1,6 @@ use rustc_middle::mir::*; use rustc_middle::ty::{self, TyCtxt}; +use rustc_target::abi::Align; /// Returns `true` if this place is allowed to be less aligned /// than its containing struct (because it is within a packed @@ -14,17 +15,25 @@ where L: HasLocalDecls<'tcx>, { debug!("is_disaligned({:?})", place); - if !is_within_packed(tcx, local_decls, place) { - debug!("is_disaligned({:?}) - not within packed", place); - return false; - } + let pack = match is_within_packed(tcx, local_decls, place) { + None => { + debug!("is_disaligned({:?}) - not within packed", place); + return false; + } + Some(pack) => pack, + }; let ty = place.ty(local_decls, tcx).ty; match tcx.layout_raw(param_env.and(ty)) { - Ok(layout) if layout.align.abi.bytes() == 1 => { - // if the alignment is 1, the type can't be further - // disaligned. - debug!("is_disaligned({:?}) - align = 1", place); + Ok(layout) if layout.align.abi <= pack => { + // If the packed alignment is greater or equal to the field alignment, the type won't be + // further disaligned. + debug!( + "is_disaligned({:?}) - align = {}, packed = {}; not disaligned", + place, + layout.align.abi.bytes(), + pack.bytes() + ); false } _ => { @@ -34,7 +43,11 @@ where } } -fn is_within_packed<'tcx, L>(tcx: TyCtxt<'tcx>, local_decls: &L, place: Place<'tcx>) -> bool +fn is_within_packed<'tcx, L>( + tcx: TyCtxt<'tcx>, + local_decls: &L, + place: Place<'tcx>, +) -> Option where L: HasLocalDecls<'tcx>, { @@ -45,7 +58,7 @@ where ProjectionElem::Field(..) => { let ty = place_base.ty(local_decls, tcx).ty; match ty.kind() { - ty::Adt(def, _) if def.repr.packed() => return true, + ty::Adt(def, _) => return def.repr.pack, _ => {} } } @@ -53,5 +66,5 @@ where } } - false + None } diff --git a/src/test/ui/lint/unaligned_references.rs b/src/test/ui/lint/unaligned_references.rs index ad38c21d96c..d06b06b504f 100644 --- a/src/test/ui/lint/unaligned_references.rs +++ b/src/test/ui/lint/unaligned_references.rs @@ -8,6 +8,13 @@ pub struct Good { aligned: [u8; 32], } +#[repr(packed(2))] +pub struct Packed2 { + x: u32, + y: u16, + z: u8, +} + fn main() { unsafe { let good = Good { data: 0, ptr: &0, data2: [0, 0], aligned: [0; 32] }; @@ -32,4 +39,12 @@ fn main() { let _ = &good.aligned; // ok, has align 1 let _ = &good.aligned[2]; // ok, has align 1 } + + unsafe { + let packed2 = Packed2 { x: 0, y: 0, z: 0 }; + let _ = &packed2.x; //~ ERROR reference to packed field + //~^ previously accepted + let _ = &packed2.y; // ok, has align 2 in packed(2) struct + let _ = &packed2.z; // ok, has align 1 + } } diff --git a/src/test/ui/lint/unaligned_references.stderr b/src/test/ui/lint/unaligned_references.stderr index 9ae25f5b59e..b4cce3cfea2 100644 --- a/src/test/ui/lint/unaligned_references.stderr +++ b/src/test/ui/lint/unaligned_references.stderr @@ -1,5 +1,5 @@ error: reference to packed field is unaligned - --> $DIR/unaligned_references.rs:15:17 + --> $DIR/unaligned_references.rs:22:17 | LL | let _ = &good.ptr; | ^^^^^^^^^ @@ -14,7 +14,7 @@ LL | #![deny(unaligned_references)] = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) error: reference to packed field is unaligned - --> $DIR/unaligned_references.rs:17:17 + --> $DIR/unaligned_references.rs:24:17 | LL | let _ = &good.data; | ^^^^^^^^^^ @@ -24,7 +24,7 @@ LL | let _ = &good.data; = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) error: reference to packed field is unaligned - --> $DIR/unaligned_references.rs:20:17 + --> $DIR/unaligned_references.rs:27:17 | LL | let _ = &good.data as *const _; | ^^^^^^^^^^ @@ -34,7 +34,7 @@ LL | let _ = &good.data as *const _; = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) error: reference to packed field is unaligned - --> $DIR/unaligned_references.rs:22:27 + --> $DIR/unaligned_references.rs:29:27 | LL | let _: *const _ = &good.data; | ^^^^^^^^^^ @@ -44,7 +44,7 @@ LL | let _: *const _ = &good.data; = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) error: reference to packed field is unaligned - --> $DIR/unaligned_references.rs:25:17 + --> $DIR/unaligned_references.rs:32:17 | LL | let _ = good.data.clone(); | ^^^^^^^^^ @@ -54,7 +54,7 @@ LL | let _ = good.data.clone(); = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) error: reference to packed field is unaligned - --> $DIR/unaligned_references.rs:28:17 + --> $DIR/unaligned_references.rs:35:17 | LL | let _ = &good.data2[0]; | ^^^^^^^^^^^^^^ @@ -63,5 +63,15 @@ LL | let _ = &good.data2[0]; = note: for more information, see issue #82523 = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) -error: aborting due to 6 previous errors +error: reference to packed field is unaligned + --> $DIR/unaligned_references.rs:45:17 + | +LL | let _ = &packed2.x; + | ^^^^^^^^^^ + | + = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release! + = note: for more information, see issue #82523 + = note: fields of packed structs are not properly aligned, and creating a misaligned reference is undefined behavior (even if that reference is never dereferenced) + +error: aborting due to 7 previous errors