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|
use rustc_index::IndexVec;
use rustc_middle::mir::interpret::Scalar;
use rustc_middle::mir::visit::PlaceContext;
use rustc_middle::mir::*;
use rustc_middle::ty::{Ty, TyCtxt};
use rustc_session::Session;
use crate::check_pointers::{BorrowCheckMode, PointerCheck, check_pointers};
pub(super) struct CheckAlignment;
impl<'tcx> crate::MirPass<'tcx> for CheckAlignment {
fn is_enabled(&self, sess: &Session) -> bool {
// FIXME(#112480) MSVC and rustc disagree on minimum stack alignment on x86 Windows
if sess.target.llvm_target == "i686-pc-windows-msvc" {
return false;
}
sess.ub_checks()
}
fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
// Skip trivially aligned place types.
let excluded_pointees = [tcx.types.bool, tcx.types.i8, tcx.types.u8];
// We have to exclude borrows here: in `&x.field`, the exact
// requirement is that the final reference must be aligned, but
// `check_pointers` would check that `x` is aligned, which would be wrong.
check_pointers(
tcx,
body,
&excluded_pointees,
insert_alignment_check,
BorrowCheckMode::ExcludeBorrows,
);
}
fn is_required(&self) -> bool {
true
}
}
/// Inserts the actual alignment check's logic. Returns a
/// [AssertKind::MisalignedPointerDereference] on failure.
fn insert_alignment_check<'tcx>(
tcx: TyCtxt<'tcx>,
pointer: Place<'tcx>,
pointee_ty: Ty<'tcx>,
_context: PlaceContext,
local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>,
stmts: &mut Vec<Statement<'tcx>>,
source_info: SourceInfo,
) -> PointerCheck<'tcx> {
// Cast the pointer to a *const ().
let const_raw_ptr = Ty::new_imm_ptr(tcx, tcx.types.unit);
let rvalue = Rvalue::Cast(CastKind::PtrToPtr, Operand::Copy(pointer), const_raw_ptr);
let thin_ptr = local_decls.push(LocalDecl::with_source_info(const_raw_ptr, source_info)).into();
stmts
.push(Statement { source_info, kind: StatementKind::Assign(Box::new((thin_ptr, rvalue))) });
// Transmute the pointer to a usize (equivalent to `ptr.addr()`).
let rvalue = Rvalue::Cast(CastKind::Transmute, Operand::Copy(thin_ptr), tcx.types.usize);
let addr = local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
stmts.push(Statement { source_info, kind: StatementKind::Assign(Box::new((addr, rvalue))) });
// Get the alignment of the pointee
let alignment =
local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
let rvalue = Rvalue::NullaryOp(NullOp::AlignOf, pointee_ty);
stmts.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((alignment, rvalue))),
});
// Subtract 1 from the alignment to get the alignment mask
let alignment_mask =
local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
let one = Operand::Constant(Box::new(ConstOperand {
span: source_info.span,
user_ty: None,
const_: Const::Val(ConstValue::Scalar(Scalar::from_target_usize(1, &tcx)), tcx.types.usize),
}));
stmts.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((
alignment_mask,
Rvalue::BinaryOp(BinOp::Sub, Box::new((Operand::Copy(alignment), one))),
))),
});
// BitAnd the alignment mask with the pointer
let alignment_bits =
local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
stmts.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((
alignment_bits,
Rvalue::BinaryOp(
BinOp::BitAnd,
Box::new((Operand::Copy(addr), Operand::Copy(alignment_mask))),
),
))),
});
// Check if the alignment bits are all zero
let is_ok = local_decls.push(LocalDecl::with_source_info(tcx.types.bool, source_info)).into();
let zero = Operand::Constant(Box::new(ConstOperand {
span: source_info.span,
user_ty: None,
const_: Const::Val(ConstValue::Scalar(Scalar::from_target_usize(0, &tcx)), tcx.types.usize),
}));
stmts.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((
is_ok,
Rvalue::BinaryOp(BinOp::Eq, Box::new((Operand::Copy(alignment_bits), zero.clone()))),
))),
});
// Emit a check that asserts on the alignment and otherwise triggers a
// AssertKind::MisalignedPointerDereference.
PointerCheck {
cond: Operand::Copy(is_ok),
assert_kind: Box::new(AssertKind::MisalignedPointerDereference {
required: Operand::Copy(alignment),
found: Operand::Copy(addr),
}),
}
}
|
