fix: seqLoadStatus OOB reads/writes for custom SAF sequences (#5706) - #6917
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serprex
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July 13, 2026 02:27
Custom SAF sequence IDs can exceed sequenceMapSize, causing out-of-bounds reads/writes on the seqLoadStatus byte array (sized exactly sequenceMapSize). This is the direct cause of intermittent battle music failure with BGM packs (issue HarbourMasters#5706): on the second encounter, AudioLoad_SyncLoadSeq reads a garbage value from heap memory past seqLoadStatus[] and may find 1 (loading in progress), causing it to return NULL early — the sequence player is never initialized and no battle music plays. Symmetric fix to the fontLoadStatus guards in PR HarbourMasters#6916: - AudioLoad_IsSeqLoadComplete: return true for OOB seqIds (custom SAF sequences are resource-manager-backed, not in the async-load status table) - AudioLoad_SetSeqLoadStatus: skip update for seqId >= sequenceMapSize - AudioLoad_SyncLoadSeq: skip the in-progress check for OOB seqIds Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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What this fixes
With a custom music pack (BGM replacement) installed, battle music often fails to play — the first enemy encounter might work, but re-approaching enemies frequently gives silence. Fixes #5706.
Why it happens
The audio engine keeps a small "is this sequence loaded yet?" status array (
seqLoadStatus). It is sized for the game's built-in sequences only.Custom sequences loaded from a pack are given ID numbers that start past the end of that array. But three spots in the loader still index the array with the sequence's ID directly. When the ID belongs to a custom sequence, that index lands past the end of the array, in unrelated memory — an out-of-bounds (OOB) access:
That garbage read is what breaks battle music: if the leftover byte happens to look like "still loading," the loader gives up early and the sequence player is never started, so no music plays. Because the value depends on whatever was previously in that memory, the failure is intermittent — which is why it usually works the first time and fails on later encounters.
The fix
Custom sequences aren't tracked in that status array at all — they're served on demand by the resource manager and are always ready. So the fix simply teaches those three spots to recognize an out-of-range ID and skip the array:
This mirrors the already-merged fix for the font status array (#6916), which was the same bug on the sound-font side.
Test plan
Build Artifacts