Increase PAS_COMPACT_PTR_SIZE to 4 to raise compact heap reservation from 128MB to 32GB

[dylan-conway]

Fixes SIGILL crash from PAS_ASSERT when immortal heap metadata exhausts the 128MB compact reservation on processes with >50GB of live bmalloc heap.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 3f6a01f5-d3a4-44c0-a64c-178889e5ae68

📥 Commits

Reviewing files that changed from the base of the PR and between 00e8255 and deaedaa.

📒 Files selected for processing (1)

• Source/bmalloc/libpas/src/libpas/pas_config.h

---

Walkthrough

A macro constant PAS_COMPACT_PTR_SIZE was updated from 3llu to 4llu in the libpas configuration header. This change affects pointer size interpretation and subsequent calculations derived from this value. No control flow or conditional compilation logic was modified.

Changes

Cohort / File(s)	Summary
Configuration Macro Update Source/bmalloc/libpas/src/libpas/pas_config.h	Updated PAS_COMPACT_PTR_SIZE from 3llu to 4llu, affecting pointer size interpretation and related computations like PAS_COMPACT_PTR_BITS and PAS_COMPACT_PTR_MASK.

🚥 Pre-merge checks | ✅ 1 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Description check	⚠️ Warning	The description explains the bug being fixed (SIGILL crash from PAS_ASSERT), but lacks the required Bugzilla link, reviewer attribution, and detailed commit message structure specified in the template.	Add Bugzilla bug reference, 'Reviewed by' line, and format as proper commit message following the WebKit PR template structure.

✅ Passed checks (1 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main change: increasing PAS_COMPACT_PTR_SIZE from 3 to 4, with concrete impact metrics (128MB to 32GB heap reservation).

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

---

_{Comment @coderabbitai help to get the list of available commands and usage tips.}

[github-actions]

Preview Builds

Commit	Release	Date
deaedaa2	autobuild-preview-pr-175-deaedaa2	2026-03-10 22:36:40 UTC