Zero Division Error on latest main branch

[LiuJiazheng]

Statement

Program crashes on setup stage

Case

Any wasm,

--host standard -k 18 --function zkmain --param params --output ./output --wasm "fibonacci-guest"/target/guest.wasm setup
write params K=18 to "params/K18.params"
write params K=22 to "params/K22.params"
quotient_poly_degree 4
Start:   Assign
··Start:   Init range chip
··End:     Init range chip .........................................................55.401ms
··Start:   Assign external host call table
··End:     Assign external host call table .........................................18.501ms
··Start:   Prepare memory info for etable
··End:     Prepare memory info for etable ..........................................1.092µs
··Start:   Assign etable
··End:     Assign etable ...........................................................2.203ms
··Start:   Assign mtable
··End:     Assign mtable ...........................................................2.118ms
··Start:   Assign frame table
··End:     Assign frame table ......................................................2.953ms
··Start:   Assign bit table
··End:     Assign bit table ........................................................8.997ms
··Start:   Prepare memory info for etable
··End:     Prepare memory info for etable ..........................................50ns
··Start:   Assign etable
··End:     Assign etable ...........................................................3.596ms
··Start:   Assign mtable
··End:     Assign mtable ...........................................................3.549ms
··Start:   Assign frame table
··End:     Assign frame table ......................................................1.229ms
··Start:   Assign bit table
··End:     Assign bit table ........................................................7.629ms
··Start:   Assign context cont chip
··End:     Assign context cont chip ................................................1.282µs
··Start:   Assign Image Table
··End:     Assign Image Table ......................................................429.771µs
End:     Assign ....................................................................116.090ms
thread 'main' panicked at 'attempt to divide by zero', /home/frank/.cargo/git/checkouts/halo2-gpu-specific-4d08aed75011eb52/9ac1080/halo2_proofs/src/arithmetic.rs:426:24
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

The code:

#[cfg(feature = "cuda")]
pub fn gpu_multiexp_bound<C: CurveAffine>(
    coeffs: &[C::Scalar],
    bases: &[C],
    max_bits: usize,
) -> C::Curve {
    use ec_gpu_gen::rust_gpu_tools::Device;
    use std::str::FromStr;

    if max_bits == 0 || coeffs.len() == 0 {
        C::Curve::identity()
    } else {
        //let timer = start_timer!(|| "msm gpu");
        let n_gpu = *crate::plonk::N_GPU;
        let part_len = (coeffs.len() + n_gpu - 1) / n_gpu;

        let c = coeffs
            .par_chunks(part_len)
            .zip(bases.par_chunks(part_len))
            .map(|(c, b)| gpu_multiexp_single_gpu_with_bound(c, b, max_bits))
            .collect::<Vec<_>>()
            .into_iter()
            .reduce(|acc, x| acc + x)
            .unwrap();

        //end_timer!(timer);
        c
    }
}

Guess N_GPU is initialized as 0 but somehow not been updated ever since.

Git commit

commit 7b18f0d75546136de76f24ff365627c49c913731 (HEAD -> main, origin/main, origin/HEAD)
Author: Zhang Junyu <junyu92@gmail.com>
Date:   Sat Feb 3 21:19:47 2024 +0800

WAT

In case you need a small WASM:

(module
  (type (;0;) (func (result i64)))
  (type (;1;) (func (param i32) (result i64)))
  (type (;2;) (func (param i32)))
  (type (;3;) (func))
  (import "env" "wasm_input" (func (;0;) (type 1)))
  (import "env" "require" (func (;1;) (type 2)))
  (func (;2;) (type 0) (result i64)
    i32.const 1
    call 0)
  (func (;3;) (type 0) (result i64)
    i32.const 0
    call 0)
  (func (;4;) (type 3)
    i32.const 0
    call 0
    i32.const 0
    call 0
    i64.add
    i32.const 1
    call 0
    i64.eq
    call 1)
  (memory (;0;) 0)
  (export "read_public_input" (func 2))
  (export "read_private_input" (func 3))
  (export "zkmain" (func 4))
  (export "memory" (memory 0)))

[LiuJiazheng]

FYI, tag v1.2 is fine. Just one commit among a few between v1.2 and head shall be blamed.

[junyu0312]

The reason is no available GPU can be detected, maybe you could check your driver, or build zkWasm without '--features cuda'. The commit changed basically nothing except renaming a structure.