{"record":{"id":"c796525c2c7bc4cc","repo":"wasmerio/wasmer","slug":"failed-to-load-newly-built-in-memory-module-e","errorCode":null,"errorMessage":"Failed to load newly built in-memory module: {e}","messagePattern":"Failed to load newly built in-memory module: (.+?)","errorType":"panic","errorClass":null,"httpStatus":null,"severity":"critical","filePath":"lib/wasix/src/syscalls/wasix/closure_prepare.rs","lineNumber":387,"sourceCode":"    let wasm_bytes = build_closure_wasm_bytes(\n        &module_name,\n        closure,\n        backing_function,\n        environment.offset().into(),\n        &argument_types,\n        &result_types,\n    );\n\n    let ld_library_path: [&Path; 0] = [];\n    let wasm_loader = DlModuleSpec::Memory {\n        module_name: &module_name,\n        bytes: &wasm_bytes,\n    };\n    let module_handle = match linker.load_module(wasm_loader, &mut ctx) {\n        Ok(m) => m,\n        Err(e) => {\n            // Should never happen\n            panic!(\"Failed to load newly built in-memory module: {e}\");\n        }\n    };\n\n    return Ok(Errno::Success);\n}\n","sourceCodeStart":369,"sourceCodeEnd":393,"githubUrl":"https://github.com/wasmerio/wasmer/blob/8c4b9ee9d33fb2068863fbb3d328683e7e6ff7f5/lib/wasix/src/syscalls/wasix/closure_prepare.rs#L369-L393","documentation":"closure_prepare builds a WASM module in memory (build_closure_wasm_bytes) and immediately loads it through the instance linker. If that freshly generated module fails to validate or instantiate, the code panics with \"Failed to load newly built in-memory module\", on the assumption the generated bytes are always valid. This indicates a bug in the generator or an incompatible loader, not user data corruption.","triggerScenarios":"Invoking the closure_prepare syscall; linker.load_module rejects the just-built module bytes (validation error, unsupported feature like V128 without SIMD enabled, dylink.0 handling failure, or loader mismatch).","commonSituations":"Runtime compiled without SIMD support while closure signatures include V128; wasmer version mismatch where the generated dylink.0 section is not accepted; internal generator bug producing malformed WASM.","solutions":["Inspect the wrapped error `e` in the panic message to identify the validation failure (e.g. unsupported opcode).","Remove V128 types from the closure signature if the runtime/engine lacks SIMD support.","Upgrade or align wasmer/wasix versions so the dylink.0 module loader matches the generator.","File a bug with the panic's inner error; this path is documented as 'should never happen'."],"exampleFix":"// before\nlet signature_with_v128 = &[ValType::V128];\n// after\nlet signature = &[ValType::I32]; // avoid V128 when engine lacks SIMD","handlingStrategy":"try-catch","validationCode":"// Ensure the engine supports SIMD before using v128 in closure signatures\nassert!(engine.features().simd(), \"SIMD required for v128 closure params\");","typeGuard":null,"tryCatchPattern":"// Around the syscall boundary, catch the resulting process abort in tests:\nlet result = std::panic::catch_unwind(|| closure_prepare(...));\nif result.is_err() { /* regenerate closure or fall back to manual trampoline */ }","preventionTips":["Keep wasmer, wasix, and the loader versions aligned (single release train).","Validate generated closure signatures against enabled engine features (SIMD, reference types).","Run closure smoke tests in CI so generated-module load failures surface early.","Report generator bugs with the inner loader error message."],"tags":["wasix","panic","closures","wasm-validation","dynamic-linking"],"backgroundTag":"module-validation-failed","analyzedSha":"8c4b9ee9d33fb2068863fbb3d328683e7e6ff7f5","analyzedAt":"2026-09-01T23:06:31.009Z","contentChangedAt":null,"schemaVersion":2},"datasetVersion":"2026-09-09T06:17:21.866Z"}