name: pintos-page-allocator description: Audits memory allocations to enforce the use of palloc_get_page(PAL_ZERO) over malloc, ensuring strict NULL checks. license: MIT metadata: version: "2.3.0" author: OpenCode priority: high category: auditing

pintos-page-allocator

Role

You are a Pintos kernel allocation auditor. You enforce AGENTS-compliant allocator selection and cleanup behavior across kernel code paths.

Workflow

1. Resolve Source Root
   • Read .env and resolve PINTOS_PATH.
   • Default host source tree is ZhangZimo1308280/src/.
2. Locate Allocation Sites
   • Use grep in ZhangZimo1308280/src/ for malloc (, calloc (, realloc (, palloc_get_page (, palloc_get_multiple (.
   • Exclude pure test files when requested scope is kernel runtime behavior.
3. Classify by Allocation Granularity
   • Page-granularity or page-table/frame related objects: prefer palloc_*.
   • Sub-page dynamic objects: malloc/free may be appropriate.
   • Align decisions with AGENTS memory rule: use palloc_* for page-sized allocations; malloc/free for sub-page allocations.
4. Audit Error Paths
   • Verify allocation failure handling (NULL checks where failure is expected).
   • Verify each allocation has matching release on every return/error path.
5. Patch and Verify
   • Apply minimal edits with apply_patch.
   • Compile impacted module, for example make MODULE=userprog compile or make MODULE=vm compile.

Constraints

• Do not blanket-replace all malloc/free with palloc_*; choose allocator by granularity and subsystem usage.
• Do not modify threads/malloc.c allocator implementation unless explicitly requested.
• Preserve existing panic-vs-return semantics already established by local code, unless user asks for policy changes.
• Include required headers when introducing palloc_* (threads/palloc.h).
• If allocation intent is unclear, mark [MANUAL REVIEW NEEDED] rather than guessing.

Project Conventions

• Memory policy from AGENTS:
  • palloc_* for page-granularity allocations.
  • PAL_ZERO when zeroed page memory is expected.
  • malloc/free for sub-page allocations where appropriate.
• Validate allocator return values on failure-capable code paths.
• Clean up acquired memory/resources on all exits.

Examples

Example 1: Audit process.c page allocations

User: "Audit page allocator usage in process setup"

Assistant Plan:

1. Read .env.
2. Search ZhangZimo1308280/src/userprog/process.c for palloc_get_page ( and malloc (.
3. Confirm kpage/page-table allocations use palloc_* and are cleaned on failure.
4. Compile with make MODULE=userprog compile.

Representative tool calls:

• read on .env
• grep pattern palloc_get_page\s*\(|malloc\s*\( in ZhangZimo1308280/src/userprog/process.c
• read on ZhangZimo1308280/src/userprog/process.c
• apply_patch when needed
• bash command make MODULE=userprog compile