Specify aligned arena offsets without relying on host luck
Eight-byte fields happen to work on one machine because the backing buffer begins aligned; a sliced buffer starts at an odd address.
- Focused work estimate
- 1h 30m + prerequisites
- Priority in the scenario
- Medium
- Engineering practice
- Alignment · Checked arithmetic
Estimated field mix
- Systems programming80%
- Embedded and edge20%
Field percentages are editorial estimates of the ticket's engineering focus. They total 100%; they are not measured time, proficiency scores, or ownership evidence.
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Project context
A fictional telemetry collector copies decoded packet fields into a small native arena. The prototype misaligns wide values and reuses memory while readers still hold views. Create a local Rust crate or C library with generated byte fixtures; no device traffic or production allocator replacement is supplied.
Setup prerequisites
- Pointers and slices
- Integer overflow
- Memory alignment
Preceding work
No earlier ticket is required. Complete the project setup above.
Acceptance criteria
- Round every allocation to its declared power-of-two alignment
- Reject zero and unsupported alignments
- Report requested size and remaining capacity without exposing addresses
Implementation constraints
- Use checked integer arithmetic before changing the cursor.
Verification to include
- Allocate mixed one-, four-, and eight-byte records and verify every offset.
- Start near the numeric limit and confirm overflow leaves the cursor unchanged.
Deliverables
- Arena layout contract and boundary tests
Rollout and recovery
Keep the current copy path until the layout suite passes on two target architectures.
Value of the work
For the engineer: Practice representation invariants, lifetimes, unsafe-boundary review and memory diagnostics.
For the team: Review a component whose allocation failures and corruption cases are explicit before reuse in latency-sensitive code.
Evidence boundaries
Outcome Evidence: Tests, patches, and runbooks are requested deliverables. They become Outcome Evidence only through a qualified Mission and immutable Evidence IDs.
Ownership Evidence: Independent adaptation must be observed under a declared verification policy and cite immutable Evidence IDs. Completing a planning ticket establishes no Ownership Evidence.