transcode: normalize FACT transcoder i32 arguments to u32 (review) - #303
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Core wasm delivers i32 params to a JS import as signed numbers. Every other i32-taking intrinsic normalizes with `>>> 0` (intrinsics/mod.ts resource trampolines, boundary.ts realloc results); the twelve FACT transcoders did not. FACT's generated adapter validates `src_ptr + len <= memory.size` UNSIGNED (wasmtime-environ `validate_guest_pointer` extends with I64ExtendI32U), so a pointer in [2^31, 2^32) is legal once a wasm32 memory grows past 2 GiB — and arrived here negative: `Uint8Array.slice(negative)` read from the END of the buffer (silently wrong bytes), `dst[neg + i] =` was a silent no-op, `dst.set(copy, neg)` threw a non-Trap RangeError. wasmtime copies the right bytes with no trap. Normalized once, in `createTranscoder`, so the twelve arms stay untouched. Regression: transcode_high_ptr_test.ts (allocates a ~2.4 GiB memory; `ignore`d with a reason where the host cannot).
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Adversarial correctness review of
main@ 396a216, CABI track — the one divergence found in an otherwise faithful port.The twelve FACT transcoders received
srcPtr/dstPtr/lengths as signed i32 (no>>> 0, unlike every other i32-taking intrinsic). FACT validates guest pointers UNSIGNED (wasmtime-environvalidate_guest_pointerextends withI64ExtendI32U), so a pointer in [2^31, 2^32) is legal once a wasm32 memory exceeds 2 GiB — and arrived negative:slice(negative)read from the end of the buffer (silent wrong bytes), negative-index writes were silent no-ops,set(copy, negative)threw a non-Trap RangeError. wasmtime copies the right bytes.Fix: normalize once in
createTranscoder. Regression:transcode_high_ptr_test.ts(3 tests; allocates a ~2.4 GiB memory,ignored with a reason where the host cannot — it can on the CI runners' class of machine, and did locally).Gates:
just test-runtimegreen;just conformance0 failed; fulljust gatesgreen on the union of the five review PRs.Automerge armed.