Skip to content
New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Jump to bottom

Segfault in llvm codegen when compiling for target aarch64-unknown-none-softfloat #85629

Closed
nipzu opened this issue May 24, 2021 · 2 comments
Closed

Segfault in llvm codegen when compiling for target aarch64-unknown-none-softfloat #85629

nipzu opened this issue May 24, 2021 · 2 comments
Labels
C-bug Category: This is a bug.

Comments

@nipzu
Copy link
Contributor

nipzu commented May 24, 2021

Rustc triggers a segmentation fault when compiling the following code. I have tested this on both linux and windows with the latest nightly compiler. It is not possible to compile core in debug mode for aarch64-unknown-none-softfloat because of this bug. Luckily, release mode works for both core and the following example.

Code

#![feature(lang_items)]
#![feature(no_core)]
#![no_core]

#[lang = "sized"]
trait Sized {}

// #[no_mangle]
// #[allow(unconditional_recursion)]
pub fn foo() -> bool {
    foo()
}
Another offending example that doesn't use recursion:

#![feature(lang_items)]
#![feature(no_core)]
#![no_core]

#[lang = "sized"]
trait Sized {}

pub fn foo() -> bool {
    bar()
}

fn bar() -> bool {
    loop {}
}

Error output

~/D/P/segfault> rustc lib.rs --edition=2018 --crate-type lib --target aarch64-unknown-none-softfloat
fish: Job 1, 'rustc lib.rs --edition=2018 --c…' terminated by signal SIGSEGV (Address boundary error)
~/D/P/segfault [SIGSEGV]>

Critical features in target-spec

rustc --print target-spec-json -Z unstable-options --target aarch64-unknown-none-softfloat > aarch64-sf.json

aarch64-sf.json 

{
  "arch": "aarch64",
  "data-layout": "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128",
  "disable-redzone": true,
  "executables": true,
  "features": "+strict-align,-neon,-fp-armv8",
  "is-builtin": true,
  "linker": "rust-lld",
  "linker-flavor": "ld.lld",
  "llvm-target": "aarch64-unknown-none",
  "max-atomic-width": 128,
  "panic-strategy": "abort",
  "relocation-model": "static",
  "target-pointer-width": "64",
  "unsupported-abis": [
    "stdcall",
    "stdcall-unwind",
    "fastcall",
    "vectorcall",
    "thiscall",
    "thiscall-unwind",
    "win64",
    "sysv64"
  ]
}

I tried extracting the target spec and running with
rustc lib.rs --edition=2018 --crate-type lib --target aarch64-sf.json.

The critical line is "features": "+strict-align,-neon,-fp-armv8",. Setting both +neon and +fp-armv8 makes the segfault disappear. Those two features are the only difference between aarch64-unknown-none-softfloat and aarch64-unknown-none.

llvm-ir

With #[no_mange], the llvm-ir I get is
rustc lib.rs --edition=2018 --crate-type lib --target aarch64-unknown-none-softfloat --emit=llvm-ir :

; ModuleID = 'lib.3a1fbbbh-cgu.0'
source_filename = "lib.3a1fbbbh-cgu.0"
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64-unknown-none"

; Function Attrs: noredzone nounwind
define dso_local zeroext i1 @foo() unnamed_addr #0 {
start:
  %0 = call zeroext i1 @foo()
  br label %bb1

bb1:                                              ; preds = %start
  ret i1 %0
}

attributes #0 = { noredzone nounwind "target-cpu"="generic" }

Changing the return type of foo from bool to u8 makes the code compile fine. The only difference in llvm-ir is that the return type is changed from zeroext i1 to i8

llvm-ir with `u8` return type 
; ModuleID = 'lib.3a1fbbbh-cgu.0'
source_filename = "lib.3a1fbbbh-cgu.0"
target datalayout = "e-m:e-i8:8:32-i16:16:32-i64:64-i128:128-n32:64-S128"
target triple = "aarch64-unknown-none"

; Function Attrs: noredzone nounwind
define dso_local i8 @foo() unnamed_addr #0 {
start:
  %0 = call i8 @foo()
  br label %bb1

bb1:                                              ; preds = %start
  ret i8 %0
}

attributes #0 = { noredzone nounwind "target-cpu"="generic" }

Backtrace

Running `gdb` gives the following backtrace: 

#0  0x00007ffff1a874e6 in llvm::LegalizerInfo::findAction(std::vector<std::pair<unsigned short, llvm::LegalizeActions::LegalizeAction>, std::allocator<std::pair<unsigned short, llvm::LegalizeActions::LegalizeAction> > > const&, unsigned int) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#1  0x00007ffff1a85aca in llvm::LegalizerInfo::findScalarLegalAction(llvm::InstrAspect const&) const ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#2  0x00007ffff1a85f41 in llvm::LegalizerInfo::getAction(llvm::LegalityQuery const&) const ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#3  0x00007ffff1a86373 in llvm::LegalizerInfo::getAction(llvm::MachineInstr const&, llvm::MachineRegisterInfo const&) const ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#4  0x00007ffff1a513d4 in llvm::LegalizerHelper::legalizeInstrStep(llvm::MachineInstr&) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#5  0x00007ffff1a4a25f in llvm::Legalizer::legalizeMachineFunction(llvm::MachineFunction&, llvm::LegalizerInfo const&, llvm::ArrayRef<llvm::GISelChangeObserver*>, llvm::LostDebugLocObserver&, llvm::MachineIRBuilder&) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#6  0x00007ffff1a4da24 in llvm::Legalizer::runOnMachineFunction(llvm::MachineFunction&) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#7  0x00007ffff13f05fe in llvm::MachineFunctionPass::runOnFunction(llvm::Function&) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#8  0x00007ffff11ae759 in llvm::FPPassManager::runOnFunction(llvm::Function&) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#9  0x00007ffff11b55a3 in llvm::FPPassManager::runOnModule(llvm::Module&) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#10 0x00007ffff11aefc0 in llvm::legacy::PassManagerImpl::run(llvm::Module&) ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/../lib/libLLVM-12-rust-1.54.0-nightly.so
#11 0x00007ffff674e4c8 in LLVMRustWriteOutputFile ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-e924046ea34a2c7b.so
#12 0x00007ffff674317f in rustc_codegen_llvm::back::write::write_output_file ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-e924046ea34a2c7b.so
#13 0x00007ffff674628c in rustc_codegen_llvm::back::write::codegen ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-e924046ea34a2c7b.so
#14 0x00007ffff66d8b3b in rustc_codegen_ssa::back::write::finish_intra_module_work ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-e924046ea34a2c7b.so
#15 0x00007ffff66d1d6a in rustc_codegen_ssa::back::write::execute_work_item ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-e924046ea34a2c7b.so
#16 0x00007ffff672e6cc in std::sys_common::backtrace::__rust_begin_short_backtrace ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-e924046ea34a2c7b.so
#17 0x00007ffff673c76c in core::ops::function::FnOnce::call_once{{vtable.shim}} ()
    $HOME/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/bin/../lib/librustc_driver-e924046ea34a2c7b.so
#18 0x00007ffff43a2b37 in alloc::boxed::{{impl}}::call_once<(),FnOnce<()>,alloc::alloc::Global> ()
    at /rustc/f64503eb555475d65ae5503ef22439ca5dd394fd/library/alloc/src/boxed.rs:1575
#19 alloc::boxed::{{impl}}::call_once<(),alloc::boxed::Box<FnOnce<()>, alloc::alloc::Global>,alloc::alloc::Global> ()
    at /rustc/f64503eb555475d65ae5503ef22439ca5dd394fd/library/alloc/src/boxed.rs:1575
#20 std::sys::unix::thread::{{impl}}::new::thread_start () at library/std/src/sys/unix/thread.rs:71
#21 0x00007ffff42cf299 in start_thread () from /usr/lib/libpthread.so.0
#22 0x00007ffff41e6053 in clone () from /usr/lib/libc.so.6

Meta

rustc --version --verbose:

rustc 1.54.0-nightly (f64503eb5 2021-05-23)
binary: rustc
commit-hash: f64503eb555475d65ae5503ef22439ca5dd394fd
commit-date: 2021-05-23
host: x86_64-unknown-linux-gnu
release: 1.54.0-nightly
LLVM version: 12.0.1
@nipzu nipzu added the C-bug Category: This is a bug. label May 24, 2021
@adlerd
Copy link

adlerd commented Aug 17, 2021

(Since it's been a few months...)
I observed this too on a more recent nightly, still with aarch64-unknown-none-softfloat:

rustc 1.56.0-nightly (0fa319039 2021-08-12)
binary: rustc
commit-hash: 0fa3190394475a84360b34e074e719d519bc40f1
commit-date: 2021-08-12
host: x86_64-unknown-linux-gnu
release: 1.56.0-nightly
LLVM version: 12.0.1

Does not repro when building release.

This blocks doing things like forcing core to have frame pointers.

@nipzu
Copy link
Contributor Author

nipzu commented Oct 11, 2021

Seems to be fixed on current beta (1.56) and nightly, probably by #87570.

@nipzu nipzu closed this as completed Oct 11, 2021
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
Assignees
No one assigned
Labels
C-bug Category: This is a bug.
Projects
None yet
Milestone
No milestone
Development

No branches or pull requests
2 participants
@adlerd @nipzu