use rustc_hir::lang_items::LangItem;
use rustc_index::IndexVec;
use rustc_middle::mir::interpret::Scalar;
use rustc_middle::mir::visit::{MutatingUseContext, NonMutatingUseContext, PlaceContext, Visitor};
use rustc_middle::mir::*;
use rustc_middle::ty::{self, ParamEnv, Ty, TyCtxt};
use rustc_session::Session;
use tracing::{debug, trace};
pub struct CheckAlignment;
impl<'tcx> MirPass<'tcx> for CheckAlignment {
fn is_enabled(&self, sess: &Session) -> bool {
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>) {
if tcx.lang_items().get(LangItem::PanicImpl).is_none() {
return;
}
let basic_blocks = body.basic_blocks.as_mut();
let local_decls = &mut body.local_decls;
let param_env = tcx.param_env_reveal_all_normalized(body.source.def_id());
for block in (0..basic_blocks.len()).rev() {
let block = block.into();
for statement_index in (0..basic_blocks[block].statements.len()).rev() {
let location = Location { block, statement_index };
let statement = &basic_blocks[block].statements[statement_index];
let source_info = statement.source_info;
let mut finder =
PointerFinder { tcx, local_decls, param_env, pointers: Vec::new() };
finder.visit_statement(statement, location);
for (local, ty) in finder.pointers {
debug!("Inserting alignment check for {:?}", ty);
let new_block = split_block(basic_blocks, location);
insert_alignment_check(
tcx,
local_decls,
&mut basic_blocks[block],
local,
ty,
source_info,
new_block,
);
}
}
}
}
}
struct PointerFinder<'tcx, 'a> {
tcx: TyCtxt<'tcx>,
local_decls: &'a mut LocalDecls<'tcx>,
param_env: ParamEnv<'tcx>,
pointers: Vec<(Place<'tcx>, Ty<'tcx>)>,
}
impl<'tcx, 'a> Visitor<'tcx> for PointerFinder<'tcx, 'a> {
fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
match context {
PlaceContext::MutatingUse(
MutatingUseContext::Store
| MutatingUseContext::AsmOutput
| MutatingUseContext::Call
| MutatingUseContext::Yield
| MutatingUseContext::Drop,
) => {}
PlaceContext::NonMutatingUse(
NonMutatingUseContext::Copy | NonMutatingUseContext::Move,
) => {}
_ => {
return;
}
}
if !place.is_indirect() {
return;
}
let pointer = Place::from(place.local);
let pointer_ty = self.local_decls[place.local].ty;
if !pointer_ty.is_unsafe_ptr() {
trace!("Indirect, but not based on an unsafe ptr, not checking {:?}", place);
return;
}
let pointee_ty =
pointer_ty.builtin_deref(true).expect("no builtin_deref for an unsafe pointer");
if !pointee_ty.is_sized(self.tcx, self.param_env) {
debug!("Unsafe pointer, but pointee is not known to be sized: {:?}", pointer_ty);
return;
}
let element_ty = match pointee_ty.kind() {
ty::Array(ty, _) => *ty,
_ => pointee_ty,
};
if [self.tcx.types.bool, self.tcx.types.i8, self.tcx.types.u8].contains(&element_ty) {
debug!("Trivially aligned place type: {:?}", pointee_ty);
return;
}
self.pointers.push((pointer, pointee_ty));
self.super_place(place, context, location);
}
}
fn split_block(
basic_blocks: &mut IndexVec<BasicBlock, BasicBlockData<'_>>,
location: Location,
) -> BasicBlock {
let block_data = &mut basic_blocks[location.block];
let new_block = BasicBlockData {
statements: block_data.statements.split_off(location.statement_index),
terminator: block_data.terminator.take(),
is_cleanup: block_data.is_cleanup,
};
basic_blocks.push(new_block)
}
fn insert_alignment_check<'tcx>(
tcx: TyCtxt<'tcx>,
local_decls: &mut IndexVec<Local, LocalDecl<'tcx>>,
block_data: &mut BasicBlockData<'tcx>,
pointer: Place<'tcx>,
pointee_ty: Ty<'tcx>,
source_info: SourceInfo,
new_block: BasicBlock,
) {
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();
block_data
.statements
.push(Statement { source_info, kind: StatementKind::Assign(Box::new((thin_ptr, rvalue))) });
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();
block_data
.statements
.push(Statement { source_info, kind: StatementKind::Assign(Box::new((addr, rvalue))) });
let alignment =
local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
let rvalue = Rvalue::NullaryOp(NullOp::AlignOf, pointee_ty);
block_data.statements.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((alignment, rvalue))),
});
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),
}));
block_data.statements.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((
alignment_mask,
Rvalue::BinaryOp(BinOp::Sub, Box::new((Operand::Copy(alignment), one))),
))),
});
let alignment_bits =
local_decls.push(LocalDecl::with_source_info(tcx.types.usize, source_info)).into();
block_data.statements.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((
alignment_bits,
Rvalue::BinaryOp(
BinOp::BitAnd,
Box::new((Operand::Copy(addr), Operand::Copy(alignment_mask))),
),
))),
});
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),
}));
block_data.statements.push(Statement {
source_info,
kind: StatementKind::Assign(Box::new((
is_ok,
Rvalue::BinaryOp(BinOp::Eq, Box::new((Operand::Copy(alignment_bits), zero.clone()))),
))),
});
block_data.terminator = Some(Terminator {
source_info,
kind: TerminatorKind::Assert {
cond: Operand::Copy(is_ok),
expected: true,
target: new_block,
msg: Box::new(AssertKind::MisalignedPointerDereference {
required: Operand::Copy(alignment),
found: Operand::Copy(addr),
}),
unwind: UnwindAction::Unreachable,
},
});
}