2 use rustc_hir::def::DefKind;
3 use rustc_middle::middle::codegen_fn_attrs::CodegenFnAttrFlags;
4 use rustc_middle::mir::*;
5 use rustc_middle::ty::layout;
6 use rustc_middle::ty::{self, TyCtxt};
7 use rustc_target::spec::abi::Abi;
9 /// A pass that runs which is targeted at ensuring that codegen guarantees about
10 /// unwinding are upheld for compilations of panic=abort programs.
12 /// When compiling with panic=abort codegen backends generally want to assume
13 /// that all Rust-defined functions do not unwind, and it's UB if they actually
14 /// do unwind. Foreign functions, however, can be declared as "may unwind" via
15 /// their ABI (e.g. `extern "C-unwind"`). To uphold the guarantees that
16 /// Rust-defined functions never unwind a well-behaved Rust program needs to
17 /// catch unwinding from foreign functions and force them to abort.
19 /// This pass walks over all functions calls which may possibly unwind,
20 /// and if any are found sets their cleanup to a block that aborts the process.
21 /// This forces all unwinds, in panic=abort mode happening in foreign code, to
22 /// trigger a process abort.
24 pub struct AbortUnwindingCalls;
26 impl<'tcx> MirPass<'tcx> for AbortUnwindingCalls {
27 fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
28 let def_id = body.source.def_id();
29 let kind = tcx.def_kind(def_id);
31 // We don't simplify the MIR of constants at this time because that
32 // namely results in a cyclic query when we call `tcx.type_of` below.
33 let is_function = match kind {
34 DefKind::Fn | DefKind::AssocFn | DefKind::Ctor(..) => true,
35 _ => tcx.is_closure(def_id),
41 // This pass only runs on functions which themselves cannot unwind,
42 // forcibly changing the body of the function to structurally provide
43 // this guarantee by aborting on an unwind. If this function can unwind,
44 // then there's nothing to do because it already should work correctly.
46 // Here we test for this function itself whether its ABI allows
48 let body_flags = tcx.codegen_fn_attrs(def_id).flags;
49 let body_ty = tcx.type_of(def_id);
50 let body_abi = match body_ty.kind() {
51 ty::FnDef(..) => body_ty.fn_sig(tcx).abi(),
52 ty::Closure(..) => Abi::RustCall,
53 ty::Generator(..) => Abi::Rust,
54 _ => span_bug!(body.span, "unexpected body ty: {:?}", body_ty),
56 let body_can_unwind = layout::fn_can_unwind(tcx, body_flags, body_abi);
58 // Look in this function body for any basic blocks which are terminated
59 // with a function call, and whose function we're calling may unwind.
60 // This will filter to functions with `extern "C-unwind"` ABIs, for
62 let mut calls_to_terminate = Vec::new();
63 let mut cleanups_to_remove = Vec::new();
64 for (id, block) in body.basic_blocks().iter_enumerated() {
68 let terminator = match &block.terminator {
69 Some(terminator) => terminator,
72 let span = terminator.source_info.span;
74 let call_can_unwind = match &terminator.kind {
75 TerminatorKind::Call { func, .. } => {
76 let ty = func.ty(body, tcx);
77 let sig = ty.fn_sig(tcx);
78 let flags = match ty.kind() {
79 ty::FnPtr(_) => CodegenFnAttrFlags::empty(),
80 ty::FnDef(def_id, _) => tcx.codegen_fn_attrs(*def_id).flags,
81 _ => span_bug!(span, "invalid callee of type {:?}", ty),
83 layout::fn_can_unwind(tcx, flags, sig.abi())
85 TerminatorKind::Drop { .. }
86 | TerminatorKind::DropAndReplace { .. }
87 | TerminatorKind::Assert { .. }
88 | TerminatorKind::FalseUnwind { .. } => {
89 layout::fn_can_unwind(tcx, CodegenFnAttrFlags::empty(), Abi::Rust)
94 // If this function call can't unwind, then there's no need for it
95 // to have a landing pad. This means that we can remove any cleanup
98 cleanups_to_remove.push(id);
102 // Otherwise if this function can unwind, then if the outer function
103 // can also unwind there's nothing to do. If the outer function
104 // can't unwind, however, we need to change the landing pad for this
105 // function call to one that aborts.
106 if !body_can_unwind {
107 calls_to_terminate.push(id);
111 // For call instructions which need to be terminated, we insert a
112 // singular basic block which simply terminates, and then configure the
113 // `cleanup` attribute for all calls we found to this basic block we
114 // insert which means that any unwinding that happens in the functions
115 // will force an abort of the process.
116 if !calls_to_terminate.is_empty() {
117 let bb = BasicBlockData {
118 statements: Vec::new(),
120 terminator: Some(Terminator {
121 source_info: SourceInfo::outermost(body.span),
122 kind: TerminatorKind::Abort,
125 let abort_bb = body.basic_blocks_mut().push(bb);
127 for bb in calls_to_terminate {
128 let cleanup = body.basic_blocks_mut()[bb].terminator_mut().unwind_mut().unwrap();
129 *cleanup = Some(abort_bb);
133 for id in cleanups_to_remove {
134 let cleanup = body.basic_blocks_mut()[id].terminator_mut().unwind_mut().unwrap();
138 // We may have invalidated some `cleanup` blocks so clean those up now.
139 super::simplify::remove_dead_blocks(tcx, body);