Segfault when using llvm_asm memory constraint

[tuomas56]

I tried this code:

#![feature(llvm_asm)]
#![crate_type="staticlib"]

// using no_mangle to force codegen, otherwise nothing is emitted
#[no_mangle]
pub unsafe fn test() -> u32 {
    let test: u32;
    llvm_asm!("mov $$32, $0" : "=m"(test));
    test
}

I expected to see this happen:

> rustc test.rs
<no output>

Instead, this happened:

> rustc test.rs 
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x4fdb63)[0x7f6a182c2b63]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x153c0)[0x7f6a17a1f3c0]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm19SelectionDAGBuilder14visitInlineAsmERKNS_8CallBaseE+0x1621)[0x7f6a14f71c31]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm19SelectionDAGBuilder5visitERKNS_11InstructionE+0x67)[0x7f6a14f4ff07]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm16SelectionDAGISel16SelectBasicBlockENS_14ilist_iteratorINS_12ilist_detail12node_optionsINS_11InstructionELb0ELb0EvEELb0ELb1EEES6_Rb+0x12e)[0x7f6a1500f3be]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm16SelectionDAGISel20SelectAllBasicBlocksERKNS_8FunctionE+0x1a3b)[0x7f6a1500e49b]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm16SelectionDAGISel20runOnMachineFunctionERNS_15MachineFunctionE+0xb1d)[0x7f6a1500ba9d]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(+0x48c1177)[0x7f6a16f13177]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm19MachineFunctionPass13runOnFunctionERNS_8FunctionE+0xee)[0x7f6a14b3496e]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm13FPPassManager13runOnFunctionERNS_8FunctionE+0x639)[0x7f6a148f7869]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm13FPPassManager11runOnModuleERNS_6ModuleE+0x33)[0x7f6a148fe703]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm6legacy15PassManagerImpl3runERNS_6ModuleE+0x470)[0x7f6a148f80d0]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x20c41e8)[0x7f6a19e891e8]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x2050c3f)[0x7f6a19e15c3f]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x2053afc)[0x7f6a19e18afc]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x204f29b)[0x7f6a19e1429b]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x2048ada)[0x7f6a19e0dada]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x20940bc)[0x7f6a19e590bc]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x20b267c)[0x7f6a19e7767c]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/libstd-9c44f1fe63de3edb.so(rust_metadata_std_ed022288c3a1d27e+0xa8a97)[0x7f6a17aeda97]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x9609)[0x7f6a17a13609]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x43)[0x7f6a17927293]
Segmentation fault

Meta

rustc --version --verbose:

rustc 1.56.0-nightly (492723897 2021-07-29)
binary: rustc
commit-hash: 492723897e9b4db6701b3a75b72618d08a7d5319
commit-date: 2021-07-29
host: x86_64-unknown-linux-gnu
release: 1.56.0-nightly
LLVM version: 12.0.1

Backtrace

> BACKTRACE=1 rustc test.rs
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x4fdb63)[0x7f6d10697b63]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x153c0)[0x7f6d0fdf43c0]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm19SelectionDAGBuilder14visitInlineAsmERKNS_8CallBaseE+0x1621)[0x7f6d0d346c31]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm19SelectionDAGBuilder5visitERKNS_11InstructionE+0x67)[0x7f6d0d324f07]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm16SelectionDAGISel16SelectBasicBlockENS_14ilist_iteratorINS_12ilist_detail12node_optionsINS_11InstructionELb0ELb0EvEELb0ELb1EEES6_Rb+0x12e)[0x7f6d0d3e43be]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm16SelectionDAGISel20SelectAllBasicBlocksERKNS_8FunctionE+0x1a3b)[0x7f6d0d3e349b]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm16SelectionDAGISel20runOnMachineFunctionERNS_15MachineFunctionE+0xb1d)[0x7f6d0d3e0a9d]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(+0x48c1177)[0x7f6d0f2e8177]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm19MachineFunctionPass13runOnFunctionERNS_8FunctionE+0xee)[0x7f6d0cf0996e]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm13FPPassManager13runOnFunctionERNS_8FunctionE+0x639)[0x7f6d0cccc869]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm13FPPassManager11runOnModuleERNS_6ModuleE+0x33)[0x7f6d0ccd3703]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so(_ZN4llvm6legacy15PassManagerImpl3runERNS_6ModuleE+0x470)[0x7f6d0cccd0d0]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x20c41e8)[0x7f6d1225e1e8]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x2050c3f)[0x7f6d121eac3f]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x2053afc)[0x7f6d121edafc]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x204f29b)[0x7f6d121e929b]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x2048ada)[0x7f6d121e2ada]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x20940bc)[0x7f6d1222e0bc]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so(+0x20b267c)[0x7f6d1224c67c]
/home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/libstd-9c44f1fe63de3edb.so(rust_metadata_std_ed022288c3a1d27e+0xa8a97)[0x7f6d0fec2a97]
/lib/x86_64-linux-gnu/libpthread.so.0(+0x9609)[0x7f6d0fde8609]
/lib/x86_64-linux-gnu/libc.so.6(clone+0x43)[0x7f6d0fcfc293]
Segmentation fault

GDB Backtrace

Reading symbols from rustc...
(gdb) run test.rs
Starting program: /home/tuomas/.cargo/bin/rustc test.rs
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
process 12241 is executing new program: /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/rustc
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".
[New Thread 0x7fffee3ff700 (LWP 12245)]
[New Thread 0x7fffe8387700 (LWP 12246)]
[New Thread 0x7fffe7dff700 (LWP 12247)]
[New Thread 0x7fffe73ff700 (LWP 12248)]
[New Thread 0x7fffe6dff700 (LWP 12249)]

Thread 6 "opt test.6a6880" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7fffe6dff700 (LWP 12249)]
0x00007ffff1809c31 in llvm::SelectionDAGBuilder::visitInlineAsm(llvm::CallBase const&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
(gdb) bt
#0  0x00007ffff1809c31 in llvm::SelectionDAGBuilder::visitInlineAsm(llvm::CallBase const&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#1  0x00007ffff17e7f07 in llvm::SelectionDAGBuilder::visit(llvm::Instruction const&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#2  0x00007ffff18a73be in 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&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#3  0x00007ffff18a649b in llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#4  0x00007ffff18a3a9d in llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#5  0x00007ffff37ab177 in (anonymous namespace)::X86DAGToDAGISel::runOnMachineFunction(llvm::MachineFunction&) [clone .llvm.6640036156556231831] ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#6  0x00007ffff13cc96e in llvm::MachineFunctionPass::runOnFunction(llvm::Function&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#7  0x00007ffff118f869 in llvm::FPPassManager::runOnFunction(llvm::Function&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#8  0x00007ffff1196703 in llvm::FPPassManager::runOnModule(llvm::Module&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightl--Type <RET> for more, q to quit, c to continue without paging--
y.so
#9  0x00007ffff11900d0 in llvm::legacy::PassManagerImpl::run(llvm::Module&) ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.56.0-nightly.so
#10 0x00007ffff67211e8 in LLVMRustWriteOutputFile ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so
#11 0x00007ffff66adc3f in rustc_codegen_llvm::back::write::write_output_file ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so
#12 0x00007ffff66b0afc in rustc_codegen_llvm::back::write::codegen ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so
#13 0x00007ffff66ac29b in rustc_codegen_ssa::back::write::finish_intra_module_work ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so
#14 0x00007ffff66a5ada in rustc_codegen_ssa::back::write::execute_work_item ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so
#15 0x00007ffff66f10bc in std::sys_common::backtrace::__rust_begin_short_backtrace ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so
#16 0x00007ffff670f67c in core::ops::function::FnOnce::call_once{{vtable-shim}} ()
   from /home/tuomas/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-41fdbb8b89e55544.so
#17 0x00007ffff4385a97 in <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once ()
    at /rustc/492723897e9b4db6701b3a75b72618d08a7d5319/library/alloc/src/boxed.rs:1572
#18 <alloc::boxed::Box<F,A> as core::ops::function::FnOnce<Args>>::call_once ()
    at /rustc/492723897e9b4db6701b3a75b72618d08a7d5319/library/alloc/src/boxed.rs:1572
#19 std::sys::unix::thread::Thread::new::thread_start () at library/std/src/sys/unix/thread.rs:91
#20 0x00007ffff42ab609 in start_thread (arg=<optimized out>) at pthread_create.c:477
#21 0x00007ffff41bf293 in clone () at ../sysdeps/unix/sysv/linux/x86_64/clone.S:95

[jackh726]

llvm_asm is soon to be deprecated in favor of asm.

I'm not sure if we're still tracking llvm_asm issues cc @Amanieu

[Amanieu]

I'm in favor of closing all llvm_asm issues once #87590 lands.

[Amanieu]

Practically speaking, nobody is working on improving/fixing llvm_asm, so I doubt any llvm_asm bugs will ever get fixed.