2 use rustc_ast::InlineAsmOptions;
3 use rustc_middle::mir::*;
4 use rustc_middle::ty::layout;
5 use rustc_middle::ty::{self, TyCtxt};
6 use rustc_target::spec::abi::Abi;
7 use rustc_target::spec::PanicStrategy;
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 if !kind.is_fn_like() {
37 // This pass only runs on functions which themselves cannot unwind,
38 // forcibly changing the body of the function to structurally provide
39 // this guarantee by aborting on an unwind. If this function can unwind,
40 // then there's nothing to do because it already should work correctly.
42 // Here we test for this function itself whether its ABI allows
44 let body_ty = tcx.type_of(def_id);
45 let body_abi = match body_ty.kind() {
46 ty::FnDef(..) => body_ty.fn_sig(tcx).abi(),
47 ty::Closure(..) => Abi::RustCall,
48 ty::Generator(..) => Abi::Rust,
49 _ => span_bug!(body.span, "unexpected body ty: {:?}", body_ty),
51 let body_can_unwind = layout::fn_can_unwind(tcx, Some(def_id), body_abi);
53 // Look in this function body for any basic blocks which are terminated
54 // with a function call, and whose function we're calling may unwind.
55 // This will filter to functions with `extern "C-unwind"` ABIs, for
57 let mut calls_to_terminate = Vec::new();
58 let mut cleanups_to_remove = Vec::new();
59 for (id, block) in body.basic_blocks.iter_enumerated() {
63 let Some(terminator) = &block.terminator else { continue };
64 let span = terminator.source_info.span;
66 let call_can_unwind = match &terminator.kind {
67 TerminatorKind::Call { func, .. } => {
68 let ty = func.ty(body, tcx);
69 let sig = ty.fn_sig(tcx);
70 let fn_def_id = match ty.kind() {
72 &ty::FnDef(def_id, _) => Some(def_id),
73 _ => span_bug!(span, "invalid callee of type {:?}", ty),
75 layout::fn_can_unwind(tcx, fn_def_id, sig.abi())
77 TerminatorKind::Drop { .. } | TerminatorKind::DropAndReplace { .. } => {
78 tcx.sess.opts.unstable_opts.panic_in_drop == PanicStrategy::Unwind
79 && layout::fn_can_unwind(tcx, None, Abi::Rust)
81 TerminatorKind::Assert { .. } | TerminatorKind::FalseUnwind { .. } => {
82 layout::fn_can_unwind(tcx, None, Abi::Rust)
84 TerminatorKind::InlineAsm { options, .. } => {
85 options.contains(InlineAsmOptions::MAY_UNWIND)
87 _ if terminator.unwind().is_some() => {
88 span_bug!(span, "unexpected terminator that may unwind {:?}", terminator)
93 // If this function call can't unwind, then there's no need for it
94 // to have a landing pad. This means that we can remove any cleanup
97 cleanups_to_remove.push(id);
101 // Otherwise if this function can unwind, then if the outer function
102 // can also unwind there's nothing to do. If the outer function
103 // can't unwind, however, we need to change the landing pad for this
104 // function call to one that aborts.
105 if !body_can_unwind {
106 calls_to_terminate.push(id);
110 // For call instructions which need to be terminated, we insert a
111 // singular basic block which simply terminates, and then configure the
112 // `cleanup` attribute for all calls we found to this basic block we
113 // insert which means that any unwinding that happens in the functions
114 // will force an abort of the process.
115 if !calls_to_terminate.is_empty() {
116 let bb = BasicBlockData {
117 statements: Vec::new(),
119 terminator: Some(Terminator {
120 source_info: SourceInfo::outermost(body.span),
121 kind: TerminatorKind::Abort,
124 let abort_bb = body.basic_blocks_mut().push(bb);
126 for bb in calls_to_terminate {
127 let cleanup = body.basic_blocks_mut()[bb].terminator_mut().unwind_mut().unwrap();
128 *cleanup = Some(abort_bb);
132 for id in cleanups_to_remove {
133 let cleanup = body.basic_blocks_mut()[id].terminator_mut().unwind_mut().unwrap();
137 // We may have invalidated some `cleanup` blocks so clean those up now.
138 super::simplify::remove_dead_blocks(tcx, body);