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test(web): seed SD before autoboot; document upstream store-TCI root cause

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The file browser no longer auto-seeds, so the headless test seeds Test/example.txt into OPFS before autoboot. Docs corrected: store-containing-TB TCI is upstream qemu-wasm design (compiled store path is not rewind-safe), not a port bug.
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Evan Reichard
2026-07-21 16:14:22 -04:00
parent 78f181e924
commit 223500ab09
4 changed files with 45 additions and 4 deletions
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ISSUES.md
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@@ -8,11 +8,13 @@ Opening `/Test/example.txt` through QEMU `vvfat` could corrupt coroutine/guest s
`ssi-sd` consumed a write-data token while leaving response mode, then parsed payload bytes as commands. The adapter now enters token mode immediately after the final R1 byte. SPI CMD13 also uses the upstream-correct `sd_r1` internal response so status polling no longer loops on `Unexpected response to cmd 13`.
## Worked around: WASM reader panic in uzlib font decompression
## Upstream limitation: compiled wasm32 store path (perf ceiling)
Opening a book panicked **only in WASM** (`Invalid read ... reason: rejected` → Load access fault) inside `uzlib_uncompress` during the reader's font `prewarmCache`. Native QEMU from the same submodule decompresses the identical static flash font and renders text, so it is a wasm32 TCG backend miscompile, not firmware/SD.
Opening a book panics **only in WASM** (`Invalid read ... reason: rejected` → Load access fault) inside `uzlib_uncompress` during the reader's font `prewarmCache` **if** compiled guest stores are enabled. Native QEMU from the same submodule renders fine.
Worked around by forcing store-containing TBs to TCI (`wasm_tci_only_tb = true` in `tcg_out_qemu_st`). Reader now opens and paints in the browser. This is a workaround with a perf ceiling (store-containing TBs run interpreted); the precise miscompiled op is not yet localized. Full investigation and next steps: `docs/wasm-inflate-panic.md`.
Root cause (confirmed by full diff against pristine upstream): `wasm_tci_only_tb = true` in `tcg_out_qemu_st` is **upstream qemu-wasm's own design**. Upstream forces every store-containing TB to the TCI interpreter because its compiled restartable-block store path is not rewind-safe (a yielded softmmu helper replays the block; safe for loads, corrupting for stores). This is the dominant cost of book open (font inflate is store-heavy, so the hot loop never JIT-promotes).
The real fix is to make compiled stores rewind-safe and drop the blanket TCI — a substantial TCG-backend task, ~15 min per browser iteration, no native repro. Full analysis: `docs/wasm-inflate-panic.md`.
## Resolved: reader grayscale rendered inverted and muddled