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Colby MchenryandGitHub 838006c947 fix(kernel): guard the native walkers against stack overflow and defer deep files to wasm (#1581) (#1600)
Fixes #1581.

## What was wrong

`codegraph init` / `codegraph index` died with `Segmentation fault` — the whole CLI
process, not a parse worker — on a C/C++ file with very deep brace nesting (llvm's
`clang/test/Parser/parser_overflow.c`, 16,384 nested `{`). The reporter's diagnosis is
exactly right: tree-sitter's parser is iterative, so the file parses fine, and then the
native kernel's **recursive walker** (`visit_node` → `visit_for_calls_and_structure` → …,
one frame per AST level) overflowed the thread's stack. A native overflow can't be caught
the way a wasm abort can, and a parse worker is a thread of the `codegraph` process, so
the SIGSEGV took the entire indexer down — no message, no per-file fallback, no partial
index.

Two things made "just give the worker a bigger stack" the wrong fix:

- it only moves the cliff — reproduced here: the reporter's 16,384-deep file kills a
  default 4 MiB worker (rc=132 on macOS / 139 on Linux), and a 100k-deep file kills the
  8 MiB **main** thread too;
- the walkers are shared by every kernel-routed language (20 of them), and each has
  several recursion points with different frame sizes, so no single stack size is a
  provable bound.

Meanwhile the wasm path already handles this shape gracefully: its JS walker catches its
own `RangeError` per file and stores a partial result with a `parse_error`. The kernel
just needed a way to get there instead of dying.

## What this does

**The kernel guards its own recursion against the calling thread's real stack bounds and
defers a too-deep file to wasm** — the same `defer:` routing signal it already uses for
files with parse errors, which `src/extraction/kernel/index.ts` treats as "take the wasm
path for this file", silently.

- `codegraph-kernel/src/stack.rs`: per-thread stack bounds from the OS, computed once per
  thread and cached — glibc/musl `pthread_getattr_np` + `pthread_attr_getstack`, macOS
  `pthread_get_stackaddr_np` + `pthread_get_stacksize_np`, Win32
  `GetCurrentThreadStackLimits` (a hand-declared `kernel32` extern; no `windows-sys`).
  `exhausted()` is one thread-local load and one compare: true once the stack pointer is
  within a 256 KiB red zone of the limit, and it latches a flag. Where the OS can't report
  bounds it falls back to a fixed 1 MiB descent budget measured from the entry stack
  pointer — safe on anything from Node's 4 MiB worker default up. So the guard is exact on
  the 4 MiB worker, the 8 MiB main thread, and any `resourceLimits.stackSizeMb` alike.
- `stack_guard!()` (defined in `lib.rs`) is the first statement of every recursive walker
  function — all **150** self-recursive or on-cycle functions across the 15 walker modules,
  found by script (every cycle in the call graph, not just direct self-calls). It returns
  `Default::default()` (`()`, `false`, `None`, `""`) so an exhausted walk simply stops
  descending; a hook returning `false` sends its caller down the generic child walk, whose
  own guard returns at once.
- `extract_file` runs the whole walk under `stack::run_guarded`: if the flag is set
  afterwards the (truncated) result is discarded and replaced by
  `defer: nesting too deep for the native walker — wasm recovery handles it`.
- `parse-pool.ts`: a comment at `new Worker(scriptPath)` records why there is deliberately
  no `resourceLimits.stackSizeMb` bump.
- No new crates beyond `libc` as a direct unix dependency (already in `Cargo.lock`
  transitively). No wire/ABI change.

Net effect for the reporter's repo: `deep.c` goes to the wasm path, lands as
`function foo` plus a recorded parse warning, and the other 31,607 files index normally.
`CODEGRAPH_KERNEL=0` and the `exclude` workaround are no longer needed.

## Tests

**Rust unit tests** (`cargo test`, 21 passed — 7 new in `stack.rs`): the walkers for
C, C++, Rust, TypeScript and Python are driven on a **1 MiB** thread (a quarter of Node's
worker default) with 30k-deep nesting and must return `defer:` instead of crashing;
shallow files are untouched; the latch resets between runs; the OS bounds are sane on the
main thread and describe a small thread's own stack.

**`__tests__/kernel-deep-nesting.test.ts`** (new, 8 tests — skips without a staged `.node`,
fails under `CODEGRAPH_KERNEL_EXPECT=1` if the kernel is missing, like the other kernel
suites):
- every default-routed language (all 20) survives a 60k-deep expression on the main thread
  — clean result or the wasm fallback's partial result, never a crash;
- the reporter's exact 16,384-brace C file is indexed (partial) on the main thread;
- 200-deep expressions in every language still take the kernel path clean (the guard never
  trips on normal code);
- inside a **default-sized 4 MiB `worker_threads` Worker** through `dist/`: the reporter's
  `deep.c` and a 60k-deep expression in every language come back `deferred` with exit 0,
  and a normal file still extracts natively;
- end-to-end through the built CLI: `codegraph init` on a repo holding `deep.c` + `ok.c`
  exits 0 and records both files, with both functions.

**Existing kernel suites**: all 15 (`kernel-*-parity`, `kernel-scaffold`,
`kernel-retry-materialize`, `kernel-grammar-parity`) pass unchanged, 147 tests — the guard
never fires on the parity fixtures.

**Reporter's probes** (`one.js` from the issue, default 4 MiB worker, this build):
`deep.c` → `deferred`, exitCode=0 (was rc=132/139); `deep100k.c` → `deferred`, exitCode=0.
Main thread: `deep.c` / `deep100k.c` → wasm partial with
`Parse error: Maximum call stack size exceeded`; a 6,000-term binary expression and a
3,000-branch `else if` chain stay on the kernel path with clean results.

**Perf** (same `dist/`, only the `.node` swapped via `CODEGRAPH_KERNEL_PATH`; interleaved
main/new ×3, `codegraph init`, macOS arm64):

| repo | main (median) | guarded (median) | nodes / edges |
|---|---|---|---|
| express (141 files) | 0.60 s (0.58–0.65) | 0.61 s (0.58–0.61) | 1,084 / identical |
| redis (786 C/H files) | 4.44 s (4.39–4.66) | 4.49 s (4.41–4.70) | 19,942 / 76,446 identical |

Within run-to-run noise, as expected for one TLS load + compare per recursion entry.

**Linux (Docker, `node:22-bookworm`, kernel built in-container, `docker run --rm --init`)** —
the reporter's platform and the glibc `pthread_getattr_np` bounds path:

```
=== platform ===
Linux efe3cc86947b 6.12.54-linuxkit #1 SMP Tue Nov  4 21:21:47 UTC 2025 aarch64 GNU/Linux
v22.22.3
-rwxr-xr-x 1 root root 35332288 Aug 22 18:02 codegraph-kernel/prebuilds/linux-arm64/codegraph-kernel.node

=== reporter repro (issue #1581): 16,384-brace deep.c, codegraph init ===
│
└  Done

init exit code: 0
  file: deep.c
  file: deep100k.c
  file: ok.c
  function: add
  function: bar
  function: foo

=== worker probe: kernel raw extract in a default 4 MiB worker ===
deep.c: deferred
deep.c: worker exitCode=0
deep100k.c: deferred
deep100k.c: worker exitCode=0
ok.c: kernel nodes=2
ok.c: worker exitCode=0

=== cargo test stack:: (glibc pthread_getattr_np bounds path) ===
test stack::tests::os_bounds_are_sane_on_this_platform ... ok
test stack::tests::small_stack_reports_its_own_bounds ... ok
test stack::tests::normal_files_are_untouched_by_the_guard ... ok
test stack::tests::deep_braces_c_defer_instead_of_crashing ... ok
test stack::tests::latch_resets_between_runs ... ok
test stack::tests::deep_parens_cpp_rust_ts_python_defer_instead_of_crashing ... ok
test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured; 15 filtered out; finished in 0.23s

=== vitest: kernel-deep-nesting + kernel-scaffold ===
✓ __tests__/kernel-scaffold.test.ts (10 tests) 30ms
✓ __tests__/kernel-deep-nesting.test.ts (8 tests) 36989ms
Test Files  2 passed (2)
Tests  18 passed (18)
```

(The pre-fix crash was reproduced on macOS — rc=132 in a default worker, rc=139 on the main thread at 100k depth — not re-run inside this container; the reporter's Linux x86_64 trace is the SIGSEGV form of the same overflow.)

**Windows (Parallels ARM64 VM, MSVC 14.44, `cargo 1.97`, kernel built on the VM,
`GetCurrentThreadStackLimits` path)**:

```
head: cbf8485 fix(kernel): guard the native walkers against stack overflow and defer deep files to wasm (#1581)
=== cargo build --release (win32-arm64) ===
    Finished `release` profile [optimized] target(s) in 2m 04s
staged: 35086848 bytes
=== cargo test (stack guard unit tests) ===
test stack::tests::normal_files_are_untouched_by_the_guard ... ok
test stack::tests::os_bounds_are_sane_on_this_platform ... ok
test stack::tests::small_stack_reports_its_own_bounds ... ok
test stack::tests::deep_braces_c_defer_instead_of_crashing ... ok
test stack::tests::latch_resets_between_runs ... ok
test stack::tests::deep_parens_cpp_rust_ts_python_defer_instead_of_crashing ... ok
test result: ok. 6 passed; 0 failed; 0 ignored; 0 measured; 15 filtered out; finished in 0.49s
=== reporter repro: codegraph init on a 16,384-brace deep.c ===
└  Done
init exit code: 0
=== vitest: deep-nesting + scaffold (CODEGRAPH_KERNEL_EXPECT=1) ===
✓ __tests__/kernel-scaffold.test.ts (10 tests) 55ms
✓ __tests__/kernel-deep-nesting.test.ts (8 tests) 67239ms
   ✓ every default-routed language survives a 60k-deep expression on the main thread 52801ms
   ✓ inside a default-sized (4 MiB) parse worker, through dist/ > defers a 60k-deep expression in every default-routed language 13050ms
   ✓ end-to-end: codegraph init on a repo holding the deep file > exits 0 and records deep.c alongside the normal files 936ms
Test Files  2 passed (2)
Tests  18 passed (18)
```

(The end-to-end test is what reads the Windows index back through `node:sqlite` — `files` = `deep.c`, `ok.c`; functions `add`, `foo`.)

Full `npm test` on this branch (macOS arm64, kernel staged): **190 files passed, 3,185 tests passed, 10 skipped, 0 failed.**

Clippy note: `cargo clippy` on the current toolchain (1.92) reports 18 pre-existing lints
(`manual_contains`, `unnecessary_to_owned`, …) in walker code this PR only touched by
inserting guard lines; none are in `stack.rs`/`lib.rs`. Left alone to keep the diff
reviewable.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

https://claude.ai/code/session_01LxZj6W6Y1SHXwvpT3uwJpK
2026-08-26 10:38:29 -05:00

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3.3 KiB
TOML

[package]
name = "codegraph-kernel"
version = "0.1.0"
edition = "2021"
license = "MIT"
publish = false
description = "Native extraction kernel for CodeGraph — tree-sitter parse+extract with one JS boundary crossing per file"
[lib]
crate-type = ["cdylib"]
[dependencies]
napi = { version = "3", default-features = false, features = ["napi8"] }
napi-derive = "3"
tree-sitter = "0.25"
sha2 = "0.10"
regex = "1"
# Grammars — MUST stay revision-matched with the wasm grammars the fallback
# path loads (tree-sitter-wasms npm package / src/extraction/wasm/). The
# kernel-grammar-parity test asserts node-kind-table equality at test time;
# bump these together with the wasm side or that gate fails.
tree-sitter-typescript = "0.23"
tree-sitter-javascript = "0.25"
tree-sitter-java = "0.23"
tree-sitter-python = "0.23"
tree-sitter-go = "0.23"
# Pinned exact: the vendored wasm (src/extraction/wasm/) was built from these
# tags' checked-in parser.c, sha-matched against these registry tarballs
# (R7a prep, #1345). A patch bump here without re-vendoring breaks the match.
tree-sitter-c = "=0.24.2"
tree-sitter-cpp = "=0.23.4"
tree-sitter-rust = "=0.24.2"
# csharp: the vendored wasm (#717) predates the kernel and was verified
# table-identical to this crate's tarball (ABI 15, STATE_COUNT 8053, node-kind
# and field tables — csharp checklist header). Bump crate + wasm together.
tree-sitter-c-sharp = "=0.23.5"
# ruby: content bump, ABI stays 14 (the v0.23.1 tag predates the ABI-15
# generator) — kernel-grammar-parity asserts same-revision, not same-ABI.
tree-sitter-ruby = "=0.23.1"
# php: the walker calls LANGUAGE_PHP (the full HTML-interleaving variant the
# wasm ships) — NEVER LANGUAGE_PHP_ONLY, which errors on leading HTML.
tree-sitter-php = "=0.24.2"
# swift: the vendored wasm is built from THIS crate's tarball src/ (the tag's
# checked-in parser.c is an older ABI-14 generation that can never sha-match;
# grammar.json rules are JSON-equal — swift checklist header). parser.c is
# ~20MB generated — expect slow compiles.
tree-sitter-swift = "=0.7.3"
# r: the vendored wasm IS r-lib v1.2.0 and this crate's tarball ships both
# generated artifacts sha-identical to the tag (parser.c 6221657347…,
# scanner.c 1209d11076… — r checklist §Grammar prep). ABI 14 (the tag
# predates the ABI-15 generator) — parity asserts same-revision, not
# same-ABI (ruby precedent). Bump crate + wasm together.
tree-sitter-r = "=1.2.0"
# luau: the vendored wasm IS tree-sitter-grammars v1.2.0 and this crate's
# tarball ships parser.c/scanner.c sha-identical to the tag (8f25bc17… /
# a157bb52… — lua-luau checklist §Grammar prep). ABI 14. Lua itself is
# vendored C (build.rs) — its v0.4.1 revision is not on crates.io.
tree-sitter-luau = "=1.2.0"
# tree-sitter-language: the version-agnostic LanguageFn shim for the vendored
# kotlin grammar C (see build.rs — no kotlin crate dep is possible).
tree-sitter-language = "0.1"
# Stack-bounds queries for the walker stack guard (src/stack.rs, #1581):
# pthread_getattr_np / pthread_get_stackaddr_np. Already in the lock file
# transitively; Windows uses a hand-declared kernel32 extern instead.
[target.'cfg(unix)'.dependencies]
libc = "0.2"
[build-dependencies]
napi-build = "2"
cc = "1"
[profile.release]
lto = true
codegen-units = 1
strip = "symbols"