bpf-linker core dump running pass 'BPF DAG->DAG Pattern Instruction Selection'

[l2dy]

cargo xtask build of this program crashes.

#![no_std]
#![no_main]

use aya_ebpf::{
    bindings::xdp_action,
    helpers::bpf_ktime_get_ns,
    macros::{map, xdp},
    maps::LruHashMap,
    programs::XdpContext,
};
use aya_log_ebpf::error;

#[map]
static START: LruHashMap<u32, u64> = LruHashMap::with_max_entries(1 << 10, 0);

#[xdp]
pub fn aya_crash_repro(ctx: XdpContext) -> u32 {
    match try_aya_crash_repro(ctx) {
        Ok(ret) => ret,
        Err(_) => xdp_action::XDP_ABORTED,
    }
}

fn try_aya_crash_repro(ctx: XdpContext) -> Result<u32, u32> {
    let ts = unsafe { bpf_ktime_get_ns() };
    let bucket = 0u32;
    if let Some(start_ts) = unsafe { START.get(&bucket) } {
        let latency = ts - start_ts;
        let bucket_index = latency.ilog2();
        error!(&ctx, "{}", bucket_index);
    }
    Ok(xdp_action::XDP_PASS)
}

#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> ! {
    unsafe { core::hint::unreachable_unchecked() }
}

The output is

error: linking with `bpf-linker` failed: signal: 6 (SIGABRT) (core dumped)
  |
  = note: LC_ALL="C" PATH="/home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/x86_64-unknown-linux-gnu/bin:/home/l2dy/.cargo/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/home/work/opshell/" VSLANG="1033" "bpf-linker" "--export-symbols" "/tmp/rustcBw2itW/symbols" "/tmp/rustcBw2itW/symbols.o" "/home/l2dy/aya/aya-crash-repro-ebpf/../target/bpfel-unknown-none/debug/deps/aya_crash_repro-0886bd8e8675c312.aya_crash_repro.fc631aa60ebb484-cgu.0.rcgu.o" "-L" "/home/l2dy/aya/aya-crash-repro-ebpf/../target/bpfel-unknown-none/debug/deps" "-L" "/home/l2dy/aya/aya-crash-repro-ebpf/../target/debug/deps" "-L" "/home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/bpfel-unknown-none/lib" "--cpu" "generic" "-L" "/home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/rustlib/bpfel-unknown-none/lib" "-o" "/home/l2dy/aya/aya-crash-repro-ebpf/../target/bpfel-unknown-none/debug/deps/aya_crash_repro-0886bd8e8675c312" "-O3" "--debug"
  = note: unable to open LLVM shared lib /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM-18-rust-1.81.0-nightly.so: /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM-18-rust-1.81.0-nightly.so: file too short
          PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
          Stack dump:
          0.    Running pass 'Function Pass Manager' on module 'aya_crash_repro-0886bd8e8675c312'.
          1.    Running pass 'BPF DAG->DAG Pattern Instruction Selection' on function '@aya_crash_repro'

and the crash backtrace is

(gdb) bt
#0  __pthread_kill_implementation (threadid=<optimized out>, signo=signo@entry=6, no_tid=no_tid@entry=0) at pthread_kill.c:44
#1  0x00007fd697d80fb3 in __pthread_kill_internal (signo=6, threadid=<optimized out>) at pthread_kill.c:78
#2  0x00007fd697d34d96 in __GI_raise (sig=sig@entry=6) at ../sysdeps/posix/raise.c:26
#3  0x00007fd697d2026d in __GI_abort () at abort.c:100
#4  0x00007fd693fe79d8 in llvm::report_fatal_error(llvm::Twine const&, bool) () from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#5  0x00007fd69528297e in llvm::BPFTargetLowering::LowerOperation(llvm::SDValue, llvm::SelectionDAG&) const ()
   from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#6  0x00007fd69629d739 in (anonymous namespace)::SelectionDAGLegalize::LegalizeOp(llvm::SDNode*) [clone .llvm.10772212417860934100] ()
   from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#7  0x00007fd69629ba37 in llvm::SelectionDAGISel::CodeGenAndEmitDAG() () from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#8  0x00007fd6962e8b2e in llvm::SelectionDAGISel::SelectAllBasicBlocks(llvm::Function const&) ()
   from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#9  0x00007fd6963f67ce in llvm::SelectionDAGISel::runOnMachineFunction(llvm::MachineFunction&) ()
   from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#10 0x00007fd6962609d4 in llvm::FPPassManager::runOnFunction(llvm::Function&) () from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#11 0x00007fd69625fe45 in llvm::FPPassManager::runOnModule(llvm::Module&) () from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#12 0x00007fd69681fa60 in llvm::legacy::PassManagerImpl::run(llvm::Module&) () from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#13 0x00007fd694e93492 in LLVMTargetMachineEmit(LLVMOpaqueTargetMachine*, LLVMOpaqueModule*, llvm::raw_pwrite_stream&, LLVMCodeGenFileType, char**) ()
   from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#14 0x00007fd694e93397 in LLVMTargetMachineEmitToFile () from /home/l2dy/.rustup/toolchains/nightly-x86_64-unknown-linux-gnu/lib/libLLVM.so.18.1-rust-1.81.0-nightly
#15 0x000055e3fd25eac1 in bpf_linker::llvm::codegen::{closure#0} () at src/llvm/mod.rs:302
#16 bpf_linker::llvm::Message::with<i32, bpf_linker::llvm::codegen::{closure_env#0}> () at src/llvm/mod.rs:350
#17 bpf_linker::llvm::codegen (tm=0x3f81, module=0x3f81, output=..., output_type=llvm_sys::target_machine::LLVMCodeGenFileType::LLVMAssemblyFile) at src/llvm/mod.rs:301
#18 0x000055e3fd2578b1 in bpf_linker::linker::Linker::emit (self=0x7ffd4fcabb90, output=..., output_type=llvm_sys::target_machine::LLVMCodeGenFileType::LLVMObjectFile) at src/linker.rs:505
#19 0x000055e3fd2578b1 in bpf_linker::linker::Linker::codegen (self=0x7ffd4fcabb90)
#20 bpf_linker::linker::Linker::link (self=0x7ffd4fcabb90) at src/linker.rs:268
#21 0x000055e3fd113815 in bpf_linker::main () at src/bin/bpf-linker.rs:285

[fslongjin]

I met the same problem too.

may be we cannot use ilog2 or leading_zeros

[l2dy]

I was able to workaround this issue by building bpf-linker against the latest LLVM.

Here is the patch I used on nixpkgs to install a working bpf-linker.

diff --git a/pkgs/development/tools/bpf-linker/default.nix b/pkgs/development/tools/bpf-linker/default.nix
index a9a6fed278685e8..dac83b645b0cd63 100644
--- a/pkgs/development/tools/bpf-linker/default.nix
+++ b/pkgs/development/tools/bpf-linker/default.nix
@@ -2,7 +2,7 @@
 , stdenv
 , rustPlatform
 , fetchFromGitHub
-, llvmPackages_18
+, llvmPackages_git
 , zlib
 , ncurses
 , libxml2
@@ -28,7 +28,7 @@ rustPlatform.buildRustPackage rec {
 
   buildNoDefaultFeatures = true;
 
-  nativeBuildInputs = [ llvmPackages_18.llvm ];
+  nativeBuildInputs = [ llvmPackages_git.llvm ];
   buildInputs = [ zlib ncurses libxml2 ];
 
   # fails with: couldn't find crate `core` with expected target triple bpfel-unknown-none