wasmerio/wasmer · error

unimplemented operator {operator:?}

Error message

unimplemented operator {operator:?}

What it means

The C API parser converts internal operator enums (O::...) into public wasm operators. When the conversion encounters an operator it has no mapping for, it panics with "unimplemented operator". This indicates the parser produced/reached an operator the C API layer has not implemented yet, typically a newer SIMD or relaxed-simd instruction.

Source

Thrown at lib/c-api/src/wasm_c_api/unstable/parser/operator.rs:1076

            O::I32x4TruncSatF64x2SZero => Self::I32x4TruncSatF64x2SZero,
            O::I32x4TruncSatF64x2UZero => Self::I32x4TruncSatF64x2UZero,
            O::I8x16RelaxedSwizzle => Self::I8x16RelaxedSwizzle,
            O::I32x4RelaxedTruncF32x4S => Self::I32x4RelaxedTruncSatF32x4S,
            O::I32x4RelaxedTruncF32x4U => Self::I32x4RelaxedTruncSatF32x4U,
            O::I32x4RelaxedTruncF64x2SZero => Self::I32x4RelaxedTruncSatF64x2SZero,
            O::I32x4RelaxedTruncF64x2UZero => Self::I32x4RelaxedTruncSatF64x2UZero,
            O::F32x4RelaxedMadd => Self::F32x4Fma,
            O::I8x16RelaxedLaneselect => Self::I8x16LaneSelect,
            O::I16x8RelaxedLaneselect => Self::I16x8LaneSelect,
            O::I32x4RelaxedLaneselect => Self::I32x4LaneSelect,
            O::I64x2RelaxedLaneselect => Self::I64x2LaneSelect,
            O::F32x4RelaxedMin => Self::F32x4RelaxedMin,
            O::F32x4RelaxedMax => Self::F32x4RelaxedMax,
            O::F64x2RelaxedMin => Self::F64x2RelaxedMin,
            O::F64x2RelaxedMax => Self::F64x2RelaxedMax,
            O::I16x8RelaxedQ15mulrS => Self::I16x8RelaxedQ15mulrS,
            _ => {
                panic!("unimplemented operator {operator:?}");
            }
        }
    }
}

View on GitHub (pinned to 8c4b9ee9d3)

Solutions

1. Upgrade Wasmer to a version where the operator is implemented in the C API parser.
2. Recompile the Wasm module targeting an older/standard feature set (e.g. avoid relaxed-simd: compile with -mno-relaxed-simd or disable the proposal).
3. Use the Rust API or engine-based compilation instead of the unstable C API parser, which has wider operator coverage.
4. Report/file an issue with the specific operator printed in the panic so coverage can be added.

Example fix

// before
clang --target=wasm32 -msimd128 -mrelaxed-simd -o app.wasm app.c
wasmer_module_parse(..., app.wasm) // panics on relaxed op
// after
clang --target=wasm32 -msimd128 -o app.wasm app.c // standard SIMD only

// Pre-scan module features before parsing (Wasm features section):
// reject modules declaring relaxed-simd when using the unstable C API parser
fn parser_supports(features: &WasmFeatures) -> bool {
    !features.contains(WasmFeatures::RELAXED_SIMD)
}

When it happens

Trigger: Parsing a Wasm module (via the unstable C API parser) that contains an operator whose From arm is missing — usually an uncommon SIMD or relaxed-simd op beyond those explicitly mapped — hitting the `_ => panic!` catch-all in the From impl.

Common situations: Loading modules compiled with newer wasm extensions (relaxed SIMD, new proposals) than the C API layer supports; using the unstable parser API on modules with exotic instructions; Wasmer version where an operator was added internally but not yet exposed via the C API.

Related errors

• Unhandled inner case
• not a `sys` backend!
• Unsupported backend kind {v:?}
• wasmer_env_set_memory() is not supported
• global #{} is a constant

AI-assisted analysis of wasmerio/wasmer@8c4b9ee9d3 (2026-09-01). Data as JSON: /api/errors/fb529266f3a33ab6. Report an issue: GitHub.