[AVR] compiler segfaults #107261

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1. gergoerdi

   added a commit that references this issue on Jan 24, 2023

   Segfault reproducer for rust-lang/rust#107261

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2. gergoerdi commented on Jan 24, 2023

   

   gergoerdi

   on Jan 24, 2023

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   I tried making the reproducer as small as possible, but at some point it becomes extremely sensitive to seemingly trivial changes: for example, if I remove the unused score field from Player, suddenly the segfault goes away.
3. gergoerdi commented on Jan 25, 2023

   

   gergoerdi

   on Jan 25, 2023

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   Tried it with latest nightly, crashes just the same:

   $ rustup toolchain install nightly-2023-01-24
   $ rustup component add rust-src --toolchain nightly-2023-01-24-x86_64-unknown-linux-gnu
   $ rustup override set nightly-2023-01-24
   $ cargo build --release
   ...
   error: could not compile `worduino-avr`; 2 warnings emitted
   
   Caused by:
     process didn't exit successfully: `rustc --crate-name worduino_avr src/main.rs --error-format=json --json=diagnostic-rendered-ansi,artifacts,future-incompat --diagnostic-width=150 --crate-type bin --emit=dep-info,link -C opt-level=3 -C lto -C metadata=65b5fd88837c4926 -C extra-filename=-65b5fd88837c4926 --out-dir /home/cactus/prog/rust/avr/bugs/segfault/target/avr-atmega32u4/release/deps --target /home/cactus/prog/rust/avr/bugs/segfault/avr-atmega32u4.json -L dependency=/home/cactus/prog/rust/avr/bugs/segfault/target/avr-atmega32u4/release/deps -L dependency=/home/cactus/prog/rust/avr/bugs/segfault/target/release/deps --extern avr_config=/home/cactus/prog/rust/avr/bugs/segfault/target/avr-atmega32u4/release/deps/libavr_config-9dd7198fde59ab9f.rlib --extern avr_std_stub=/home/cactus/prog/rust/avr/bugs/segfault/target/avr-atmega32u4/release/deps/libavr_std_stub-a6f7257e58f8cef6.rlib --extern 'noprelude:compiler_builtins=/home/cactus/prog/rust/avr/bugs/segfault/target/avr-atmega32u4/release/deps/libcompiler_builtins-04596a6bfc480d2b.rlib' --extern 'noprelude:core=/home/cactus/prog/rust/avr/bugs/segfault/target/avr-atmega32u4/release/deps/libcore-eac7e4ed729ade79.rlib' --extern worduino_engine=/home/cactus/prog/rust/avr/bugs/segfault/target/avr-atmega32u4/release/deps/libworduino_engine-6d2d2f69f1e30efe.rlib -Z unstable-options --emit=llvm-bc` (signal: 11, SIGSEGV: invalid memory reference)
   
4. Noratrieb commented on Jan 25, 2023

   

   Noratrieb

   on Jan 25, 2023

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   Can you try getting a backtrace where the segfault occurs by running the rustc command in a debugger?
5. Noratrieb

   added

   I-crashIssue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.Issue: The compiler crashes (SIGSEGV, SIGABRT, etc). Use I-ICE instead when the compiler panics.

   on Jan 25, 2023
6. gergoerdi commented on Jan 25, 2023

   

   gergoerdi

   on Jan 25, 2023

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   Can you try getting a backtrace where the segfault occurs by running the rustc command in a debugger?

   Sure. BTW, is your question implying that you didn't manage to reproduce this with what I've provided so far? Do let me know if I'm missing some inputs that are relevant.

   0x00007ffff2136edf in llvm::RAGreedy::calculateRegionSplitCost(llvm::LiveInterval const&, llvm::AllocationOrder&, llvm::BlockFrequency&, unsigned int&, bool) () from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   => 0x00007ffff2136edf <_ZN4llvm8RAGreedy24calculateRegionSplitCostERKNS_12LiveIntervalERNS_15AllocationOrderERNS_14BlockFrequencyERjb+4059>:	48 8b 49 10	mov    0x10(%rcx),%rcx
   (gdb) bt
   #0  0x00007ffff2136edf in llvm::RAGreedy::calculateRegionSplitCost(llvm::LiveInterval const&, llvm::AllocationOrder&, llvm::BlockFrequency&, unsigned int&, bool) () from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #1  0x00007ffff213570a in llvm::RAGreedy::tryRegionSplit(llvm::LiveInterval const&, llvm::AllocationOrder&, llvm::SmallVectorImpl<llvm::Register>&)
       () from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #2  0x00007ffff21347c4 in llvm::RAGreedy::trySplit(llvm::LiveInterval const&, llvm::AllocationOrder&, llvm::SmallVectorImpl<llvm::Register>&, llvm::SmallSet<llvm::Register, 16u, std::less<llvm::Register> > const&) ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #3  0x00007ffff20d9481 in non-virtual thunk to llvm::RAGreedy::selectOrSplit(llvm::LiveInterval const&, llvm::SmallVectorImpl<llvm::Register>&) ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #4  0x00007ffff213020c in llvm::RegAllocBase::allocatePhysRegs() ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #5  0x00007ffff2197f30 in llvm::RAGreedy::runOnMachineFunction(llvm::MachineFunction&) ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #6  0x00007ffff2387461 in llvm::FPPassManager::runOnFunction(llvm::Function&) ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #7  0x00007ffff238692f in llvm::FPPassManager::runOnModule(llvm::Module&) ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #8  0x00007ffff220b29e in llvm::legacy::PassManagerImpl::run(llvm::Module&) ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/libLLVM-15-rust-1.67.0-nightly.so
   #9  0x00007ffff6357582 in LLVMRustWriteOutputFile ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/librustc_driver-e0c8ab3d159f8c4e.so
   #10 0x00007ffff6356f45 in rustc_codegen_llvm::back::write::write_output_file ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/librustc_driver-e0c8ab3d159f8c4e.so
   #11 0x00007ffff6354e97 in rustc_codegen_llvm::back::write::codegen ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/librustc_driver-e0c8ab3d159f8c4e.so
   #12 0x00007ffff6385f9d in rustc_codegen_ssa::back::write::finish_intra_module_work::<rustc_codegen_llvm::LlvmCodegenBackend> ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/librustc_driver-e0c8ab3d159f8c4e.so
   #13 0x00007ffff6384ecc in rustc_codegen_ssa::back::write::execute_work_item::<rustc_codegen_llvm::LlvmCodegenBackend> ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/librustc_driver-e0c8ab3d159f8c4e.so
   #14 0x00007ffff6383d2e in std::sys_common::backtrace::__rust_begin_short_backtrace::<<rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::ExtraBackendMethods>::spawn_named_thread<rustc_codegen_ssa::back::write::spawn_work<rustc_codegen_llvm::LlvmCodegenBackend>::{closure#0}, ()>::{closure#0}, ()> () from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/librustc_driver-e0c8ab3d159f8c4e.so
   #15 0x00007ffff62898f4 in <<std::thread::Builder>::spawn_unchecked_<<rustc_codegen_llvm::LlvmCodegenBackend as rustc_codegen_ssa::traits::backend::ExtraBackendMethods>::spawn_named_thread<rustc_codegen_ssa::back::write::spawn_work<rustc_codegen_llvm::LlvmCodegenBackend>::{closure#0}, ()>::{closure#0}, ()>::{closure#1} as core::ops::function::FnOnce<()>>::call_once::{shim:vtable#0} ()
      from /home/cactus/.rustup/toolchains/nightly-2022-12-09-x86_64-unknown-linux-gnu/lib/librustc_driver-e0c8ab3d159f8c4e.so
   #16 0x00007ffff7c45b33 in alloc::boxed::{impl#45}::call_once<(), dyn core::ops::function::FnOnce<(), Output=()>, alloc::alloc::Global> ()
       at library/alloc/src/boxed.rs:2000
   #17 alloc::boxed::{impl#45}::call_once<(), alloc::boxed::Box<dyn core::ops::function::FnOnce<(), Output=()>, alloc::alloc::Global>, alloc::alloc::Glob--Type <RET> for more, q to quit, c to continue without paging--
   al> () at library/alloc/src/boxed.rs:2000
   #18 std::sys::unix::thread::{impl#2}::new::thread_start () at library/std/src/sys/unix/thread.rs:108
   #19 0x00007ffff3894b43 in start_thread (arg=<optimized out>) at ./nptl/pthread_create.c:442
   #20 0x00007ffff3926a00 in clone3 () at ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81
   

   ❤️React with ❤️2Reacted by nora and Jubilee
7. Noratrieb

   added

   A-LLVMArea: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.Area: Code generation parts specific to LLVM. Both correctness bugs and optimization-related issues.

   on Jan 25, 2023
8. workingjubilee

   added

   O-AVRTarget: AVR processors (ATtiny, ATmega, etc.)Target: AVR processors (ATtiny, ATmega, etc.)

   on Jan 27, 2023
9. workingjubilee commented on Feb 19, 2023

   

   workingjubilee

   on Feb 19, 2023

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   Just noting that this still reproduces even with avr-progmem 0.3.3, the latest fixes in rustc for AVR and repr(C), and turning off --emit=llvm-bc.

   👍React with 👍1Reacted by Flavio Vilante
10. gergoerdi commented on Feb 19, 2023

    

    gergoerdi

    on Feb 19, 2023

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    Hmm. Isn't it also a bug in itself if --emit=llvm-bc changes the behaviour at all?
11. workingjubilee commented on Feb 19, 2023

    

    workingjubilee

    on Feb 19, 2023

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    Oh, probably.
    That's why I noted that it is not at fault!
12. Noratrieb

    added

    T-compilerRelevant to the compiler team, which will review and decide on the PR/issue.Relevant to the compiler team, which will review and decide on the PR/issue.

    on Apr 5, 2023
13. Patryk27 commented on Jun 3, 2023

    

    Patryk27

    on Jun 3, 2023

    Last edited by Patryk27

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    fwiw, on the newest llvm-project (with debug assertions enabled), this itself:

    #![no_std]
    #![no_main]
    
    extern crate avr_std_stub;
    
    use core::{hint::black_box, panic::PanicInfo};
    
    fn reverse_bits(mut x: u8) -> u8 {
        let mut y: u8 = 0;
        let mut i = 7;
    
        while i > 0 {
            if x & 0x01 != 0 {
                y |= 0x80;
            }
    
            y = y.rotate_left(1);
            x >>= 1;
            i -= 1;
        }
    
        y
    }
    
    #[no_mangle]
    pub extern "C" fn main() {
        let x = black_box(123);
        let x = reverse_bits(x);
        let x = black_box(x);
    
        loop {
            //
        }
    }

    ... fails with:

    LLVM ERROR: Cannot select: t49: i8 = ROL t38
      t38: i8 = or t37, t50
        t37: i8 = and t60, Constant:i8<-128>
          t60: i8 = LSL t2
            t2: i8,ch = CopyFromReg t0, Register:i8 %0
              t1: i8 = Register %0
          t12: i8 = Constant<-128>
        t50: i8 = ROL t34
          t34: i8 = or t33, t51
            t33: i8 = and t61, Constant:i8<-128>
              t61: i8 = LSL t60
                t60: i8 = LSL t2
                  t2: i8,ch = CopyFromReg t0, Register:i8 %0
                    t1: i8 = Register %0
              t12: i8 = Constant<-128>
            t51: i8 = ROL t29
              t29: i8 = or t28, t52
                t28: i8 = and t62, Constant:i8<-128>
                  t62: i8 = LSL t61
                    t61: i8 = LSL t60
                      t60: i8 = LSL t2
    
                  t12: i8 = Constant<-128>
                t52: i8 = ROL t24
                  t24: i8 = or t63, t53
                    t63: i8 = and t55, Constant:i8<-128>
                      t55: i8 = <<Unknown Target Node #459>> t2
    
                      t12: i8 = Constant<-128>
                    t53: i8 = ROL t19
                      t19: i8 = or t18, t54
    

    Curiously, it works with 16-bit+ types; I'll see if there's anything I can do.

    Edit: minimized:

    define i8 @test(i8 %0) {
    start:
      %1 = call i8 @llvm.fshl.i8(i8 %0, i8 %0, i8 1)
      ret i8 %1
    }
    
    declare i8 @llvm.fshl.i8(i8, i8, i8)
    
14. Patryk27 commented on Jun 3, 2023

    

    Patryk27

    on Jun 3, 2023

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    Okie, patch submitted:
    https://reviews.llvm.org/D152063

    With that patch, compiling your application, @gergoerdi, seems to pass; I'll let know once the patch is merged and applied to rustc 🙂
15. Patryk27 commented on Jul 30, 2023

    

    Patryk27

    on Jul 30, 2023

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    Status: fixed on LLVM's side - will be solved when LLVM's version is bumped here (apparently soon ™️ ).
16. workingjubilee

    added

    llvm-fixed-upstreamIssue expected to be fixed by the next major LLVM upgrade, or backported fixesIssue expected to be fixed by the next major LLVM upgrade, or backported fixes

    on Jul 30, 2023
17. Patryk27 commented on Aug 10, 2023

    

    Patryk27

    on Aug 10, 2023

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    fwiw, this got fixed with #114048 🙂
18. nikic

    closed this as completedon Aug 10, 2023