rustc segfault when using a function as input to asm!

[stevecheckoway]

Using rustc nightly

rustc 1.42.0-nightly (fc5deca21 2019-12-21)

the following two code samples cause rustc to crash.

#![feature(asm)]

extern "C" fn foo() { }

fn main() {
    unsafe {
        asm!("callq $0" :: "s"(foo) :: "volatile");
    }
}

#![feature(asm)]

extern "C" fn foo() { }

fn main() {
    let x: usize;
    unsafe {
        asm!("movq $1, $0" : "=r"(x) : "r"(foo));
    }
    assert!(x != 0);
}

Here's a rustc backtrace for the first.

(lldb) bt
* thread #3, stop reason = EXC_BAD_ACCESS (code=1, address=0x18)
  * frame #0: 0x000000010153c761 librustc_driver-0c56519087c8b41a.dylib`llvm::TargetLowering::LowerAsmOperandForConstraint(llvm::SDValue, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::vector<llvm::SDValue, std::__1::allocator<llvm::SDValue> >&, llvm::SelectionDAG&) const + 129
    frame #1: 0x0000000100807d54 librustc_driver-0c56519087c8b41a.dylib`llvm::X86TargetLowering::LowerAsmOperandForConstraint(llvm::SDValue, std::__1::basic_string<char, std::__1::char_traits<char>, std::__1::allocator<char> >&, std::__1::vector<llvm::SDValue, std::__1::allocator<llvm::SDValue> >&, llvm::SelectionDAG&) const + 1636
    frame #2: 0x000000010149f2fa librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGBuilder::visitInlineAsm(llvm::ImmutableCallSite) + 8874
    frame #3: 0x0000000101480ee9 librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) + 105
    frame #4: 0x000000010150ecb0 librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator<llvm::ilist_detail::node_options<llvm::Instruction, false, false, void>, false, true>, llvm::ilist_iterator<llvm::ilist_detail::node_options<llvm::Instruction, false, false, void>, false, true>, bool&) + 128
    frame #5: 0x000000010150e55b librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) + 5243
    frame #6: 0x000000010150c344 librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 1748
    frame #7: 0x000000010073274d librustc_driver-0c56519087c8b41a.dylib`(anonymous namespace)::X86DAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 141
    frame #8: 0x00000001016de44d librustc_driver-0c56519087c8b41a.dylib`llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 285
    frame #9: 0x0000000101f6fab1 librustc_driver-0c56519087c8b41a.dylib`llvm::FPPassManager::runOnFunction(llvm::Function&) + 1057
    frame #10: 0x0000000101f6fdb3 librustc_driver-0c56519087c8b41a.dylib`llvm::FPPassManager::runOnModule(llvm::Module&) + 131
    frame #11: 0x0000000101f70289 librustc_driver-0c56519087c8b41a.dylib`llvm::legacy::PassManagerImpl::run(llvm::Module&) + 969
    frame #12: 0x00000001006924d3 librustc_driver-0c56519087c8b41a.dylib`LLVMRustWriteOutputFile + 563
    frame #13: 0x00000001006112e6 librustc_driver-0c56519087c8b41a.dylib`rustc_codegen_llvm::back::write::write_output_file::h76d2b2ebfb7a8eed (.llvm.10576665092353784990) + 86
    frame #14: 0x00000001006662f8 librustc_driver-0c56519087c8b41a.dylib`rustc_codegen_llvm::back::write::codegen::_$u7b$$u7b$closure$u7d$$u7d$::h66912a0fe09f03df (.llvm.3263083813660944518) + 1560
    frame #15: 0x00000001006643b3 librustc_driver-0c56519087c8b41a.dylib`rustc::util::common::time_ext::haeef6b0b58ed606e + 163
    frame #16: 0x000000010061669b librustc_driver-0c56519087c8b41a.dylib`_$LT$rustc_codegen_llvm..LlvmCodegenBackend$u20$as$u20$rustc_codegen_ssa..traits..write..WriteBackendMethods$GT$::codegen::h0f4f9d6743018805 + 3723
    frame #17: 0x000000010053e7e7 librustc_driver-0c56519087c8b41a.dylib`rustc_codegen_ssa::back::write::execute_work_item::ha12f01ddc6c02062 + 4167
    frame #18: 0x000000010065d1cf librustc_driver-0c56519087c8b41a.dylib`std::sys_common::backtrace::__rust_begin_short_backtrace::hc4efc99b4fa2ef62 + 239
    frame #19: 0x000000010060cd0b librustc_driver-0c56519087c8b41a.dylib`std::panicking::try::do_call::h223b883ec45a8b2d (.llvm.10576665092353784990) + 43
    frame #20: 0x000000010615526f libstd-fb8a2cba31c5c8b1.dylib`__rust_maybe_catch_panic + 31
    frame #21: 0x000000010051ba96 librustc_driver-0c56519087c8b41a.dylib`core::ops::function::FnOnce::call_once$u7b$$u7b$vtable.shim$u7d$$u7d$::h27c4ab159ffa15f6 + 134
    frame #22: 0x00000001061267fe libstd-fb8a2cba31c5c8b1.dylib`_$LT$alloc..boxed..Box$LT$F$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$::call_once::ha165f2d8179450a9 + 62
    frame #23: 0x0000000106153fae libstd-fb8a2cba31c5c8b1.dylib`std::sys::unix::thread::Thread::new::thread_start::h6d30401d88e22320 + 142
    frame #24: 0x00007fff62cde2eb libsystem_pthread.dylib`_pthread_body + 126
    frame #25: 0x00007fff62ce1249 libsystem_pthread.dylib`_pthread_start + 66
    frame #26: 0x00007fff62cdd40d libsystem_pthread.dylib`thread_start + 13

Here's the backtrace for the second.

(lldb) bt
* thread #2, stop reason = EXC_BAD_ACCESS (code=1, address=0x28)
  * frame #0: 0x00000001007b5374 librustc_driver-0c56519087c8b41a.dylib`llvm::X86TargetLowering::isZExtFree(llvm::SDValue, llvm::EVT) const + 4
    frame #1: 0x000000010147e086 librustc_driver-0c56519087c8b41a.dylib`llvm::RegsForValue::getCopyToRegs(llvm::SDValue, llvm::SelectionDAG&, llvm::SDLoc const&, llvm::SDValue&, llvm::SDValue*, llvm::Value const*, llvm::ISD::NodeType) const + 566
    frame #2: 0x000000010149fe6d librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGBuilder::visitInlineAsm(llvm::ImmutableCallSite) + 11805
    frame #3: 0x0000000101480ee9 librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) + 105
    frame #4: 0x000000010150ecb0 librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGISel::SelectBasicBlock(llvm::ilist_iterator<llvm::ilist_detail::node_options<llvm::Instruction, false, false, void>, false, true>, llvm::ilist_iterator<llvm::ilist_detail::node_options<llvm::Instruction, false, false, void>, false, true>, bool&) + 128
    frame #5: 0x000000010150e55b librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) + 5243
    frame #6: 0x000000010150c344 librustc_driver-0c56519087c8b41a.dylib`llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 1748
    frame #7: 0x000000010073274d librustc_driver-0c56519087c8b41a.dylib`(anonymous namespace)::X86DAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) + 141
    frame #8: 0x00000001016de44d librustc_driver-0c56519087c8b41a.dylib`llvm::MachineFunctionPass::runOnFunction(llvm::Function&) + 285
    frame #9: 0x0000000101f6fab1 librustc_driver-0c56519087c8b41a.dylib`llvm::FPPassManager::runOnFunction(llvm::Function&) + 1057
    frame #10: 0x0000000101f6fdb3 librustc_driver-0c56519087c8b41a.dylib`llvm::FPPassManager::runOnModule(llvm::Module&) + 131
    frame #11: 0x0000000101f70289 librustc_driver-0c56519087c8b41a.dylib`llvm::legacy::PassManagerImpl::run(llvm::Module&) + 969
    frame #12: 0x00000001006924d3 librustc_driver-0c56519087c8b41a.dylib`LLVMRustWriteOutputFile + 563
    frame #13: 0x00000001006112e6 librustc_driver-0c56519087c8b41a.dylib`rustc_codegen_llvm::back::write::write_output_file::h76d2b2ebfb7a8eed (.llvm.10576665092353784990) + 86
    frame #14: 0x00000001006662f8 librustc_driver-0c56519087c8b41a.dylib`rustc_codegen_llvm::back::write::codegen::_$u7b$$u7b$closure$u7d$$u7d$::h66912a0fe09f03df (.llvm.3263083813660944518) + 1560
    frame #15: 0x00000001006643b3 librustc_driver-0c56519087c8b41a.dylib`rustc::util::common::time_ext::haeef6b0b58ed606e + 163
    frame #16: 0x000000010061669b librustc_driver-0c56519087c8b41a.dylib`_$LT$rustc_codegen_llvm..LlvmCodegenBackend$u20$as$u20$rustc_codegen_ssa..traits..write..WriteBackendMethods$GT$::codegen::h0f4f9d6743018805 + 3723
    frame #17: 0x000000010053e7e7 librustc_driver-0c56519087c8b41a.dylib`rustc_codegen_ssa::back::write::execute_work_item::ha12f01ddc6c02062 + 4167
    frame #18: 0x000000010065d1cf librustc_driver-0c56519087c8b41a.dylib`std::sys_common::backtrace::__rust_begin_short_backtrace::hc4efc99b4fa2ef62 + 239
    frame #19: 0x000000010060cd0b librustc_driver-0c56519087c8b41a.dylib`std::panicking::try::do_call::h223b883ec45a8b2d (.llvm.10576665092353784990) + 43
    frame #20: 0x000000010615526f libstd-fb8a2cba31c5c8b1.dylib`__rust_maybe_catch_panic + 31
    frame #21: 0x000000010051ba96 librustc_driver-0c56519087c8b41a.dylib`core::ops::function::FnOnce::call_once$u7b$$u7b$vtable.shim$u7d$$u7d$::h27c4ab159ffa15f6 + 134
    frame #22: 0x00000001061267fe libstd-fb8a2cba31c5c8b1.dylib`_$LT$alloc..boxed..Box$LT$F$GT$$u20$as$u20$core..ops..function..FnOnce$LT$A$GT$$GT$::call_once::ha165f2d8179450a9 + 62
    frame #23: 0x0000000106153fae libstd-fb8a2cba31c5c8b1.dylib`std::sys::unix::thread::Thread::new::thread_start::h6d30401d88e22320 + 142
    frame #24: 0x00007fff62cde2eb libsystem_pthread.dylib`_pthread_body + 126
    frame #25: 0x00007fff62ce1249 libsystem_pthread.dylib`_pthread_start + 66
    frame #26: 0x00007fff62cdd40d libsystem_pthread.dylib`thread_start + 13

[Amanieu]

As a workaround you can use foo as usize.

[Amanieu]

This issue does not apply to the new asm! (RFC 2850) which automatically coerces ZST fn types to function pointers.

The legacy llvm_asm! is deprecated and is no longer maintained.