---
id: "bug-1505"
status: "fixed"
status_updated: "2026-09-24"
status_note: ""
component: "lib"
severity: "crash"
timestamp: "2026-08-07T08:10:00Z"
last_seen: "2026-09-19T09:00:00Z"
occurrences: 1
files: ["src/schema/controller.capnp"]
tags: ["controller", "ha", "wal-catchup", "capnp-schema", "codegen-limitation", "sigsegv", "uninitialized-memory", "controller.capnp", "deferred", "systemic"]
related: ["bug-1504", "bug-847"]
legacy: true
---

# bug-1505: controller_unit_test SIGSEGV in write_WalCatchupEntry (lib/controller.capnp.c)…

## Description
controller_unit_test SIGSEGV in write_WalCatchupEntry (lib/controller.capnp.c), test_wal_catchup_append_term_fields_round_trip -- discovered incidentally while chasing bug-1504; NOT fixed, logged for its own follow-up.

## Environment
_Not recorded (migrated from buglog.json)._

## Reproduction
_Not recorded (migrated from buglog.json)._

## Root cause
Same root cause as bug-1504 (Data-field codegen no-op leaves an uninitialized stack capn_ptr in the generated encode_XXX_ptr()'s local struct), a DIFFERENT field: WalCatchupEntry.payload (@2: Data), in the controller's HA/WAL-catchup subsystem (bug-847's own territory -- see controller.capnp's comment there), entirely unrelated to scheduler-core. Confirms this is a systemic, project-wide bug class affecting every `:Data` field in controller.capnp whose bytes are populated via the generic encode_XXX()/write_XXX() composite pipeline rather than fully hand-written low-level accessor code -- not a one-off. Known/suspected other Data fields with the same latent gap: ReplayHeader.configHash (dormant so far, no real consumer), CtrlHelloRequest.key, and possibly others not yet audited.

## Fix
FIXED 2026-08-07. Investigated production exposure first: xce_wal_batch_encode_raw()/wal_entry_to_wire() (request.c) never call the generic encode_WalCatchupEntry() at all -- they memset() their own struct and call write_WalCatchupEntry() directly with every field hand-set, deliberately leaving payload unset (bug-847's own comment). So this bug was 100% test-only exposure, zero production risk, confirmed by grepping every caller of encode_WalCatchupEntry_ptr/decode_WalCatchupEntry (only test_e2e_capnp.c uses the generic path). Fix: same as bug-1504 -- changed WalCatchupEntry.payload (@2) and batchPayloads (@10) from Data to List(UInt8) in controller.capnp, with batchPayloadsLen (@11, new) as batchPayloads' maplistcount companion (payload reuses the existing wirePayloadLen @9). Verified batchPayloads' own top-level-single-blob shape means this does not reintroduce bug-847's per-element cross-segment far-pointer loss (that issue is inherent to PER-ELEMENT data regardless of Data vs List(UInt8) spelling -- payload, the per-element field, was already legacy/unpopulated in production before this fix and stays that way; batchPayloads is single top-level, never subject to that issue either way). Updated typemap.h's wal_catchup_entry_t field types (xce_data_t* -> uint8_t*, new batch_payloads_wire_len). Fixed request.c's extract_data_bytes() to accept a raw capn_ptr instead of capn_data (it already only ever used .p internally) so all 4 call sites (WalCatchupEntry.payload/batchPayloads, SnapshotTransfer.payload, per-sub-entry we.payload) work regardless of which Data-shaped wrapper type the accessor returns. Strengthened test_wal_catchup_append_term_fields_round_trip (test_e2e_capnp.c) with real payload/batchPayloads content assertions (previously never exercised at all, since the test's src.payload/batch_payloads were left NULL). Verified: controller_unit_test no longer crashes (3/3 controller suite), scheduler suite unaffected (37/37, unrelated schema area).

## Verification
_Not recorded (migrated from buglog.json)._

## References
- Related: bug-1504, bug-847