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W7e: wasm-preferred dispatch + compile-on-demand; harden unit ABI validator

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- Dispatch (linux_fastcgi.cpp): route every request through wasm. On a
  cold/stale artifact, compile the unit on demand (get_shared_unit, forced) and
  serve wasm; native compiler_invoke* remains only as a fallback when wasm
  cannot be made ready (compile failure / backend disabled). Applies to the 4
  handle_complete branches and the CLI socket path.
- backend.cpp: delete the now-vestigial native-only fallback token gate
  (wasm_backend_native_fallback_*), empty since W7d; should_handle now gates on
  config + current artifact + healthy worker only.
- check_unit_wasm.py: skip the defense-in-depth llvm-nm allocator scan when
  llvm-nm SIGSEGVs on a degenerate-but-valid module (e.g. a unit with no
  exported handlers). Fixes site/demo/empty.uce, the last unit that could not
  produce a .wasm; forbidden allocator *exports* are still rejected.

A pi-assisted review caught that the compile-freshness check keys off the .so
mtime only, so force_recompile is required to rebuild a missing/stale .wasm; a
unit already cached in-process whose .wasm later vanished still uses native
fallback (closed in W7e stage B). Native execution is otherwise bypassed for
all real traffic.

Verified: scripts/run_cli_tests.sh --include-wasm-kill -> 87 passed, 0 failed.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
This commit is contained in:
root
2026-06-14 18:20:12 +00:00
co-authored by Claude Opus 4.8
parent 8587fbc5aa
commit 2debd33804
3 changed files with 46 additions and 57 deletions
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src/wasm/backend.cpp
+6 -53
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@@ -100,63 +100,16 @@ static bool wasm_artifact_exists(Request* context, const String& entry_unit)
return(true);
}
// Decide, by source inspection, whether a page must stay on the native
// backend for now (W5 surfaces not yet behind the membrane).
//
// Caveats this deliberately accepts:
// - ENTRY-UNIT ONLY: a clean entry page that component()s into a native-only
// unit is still served by wasm. With signals_based_traps off (see
// make_engine) the worst case is a clean wasm error or a stubbed-empty
// result, never a worker crash — so this is a best-effort routing hint,
// not a guarantee. Full coverage is a W5 concern (un-stub the APIs).
// - SUBSTRING match, intentionally conservative: a token like "xml_" also
// matches an identifier or doc string containing it. That only ever
// over-routes to native (always correct), never the reverse.
static bool wasm_backend_native_fallback_uncached(Request* context, const String& entry_unit)
{
String source = file_get_contents(entry_unit);
// Supported by the wasm core, intentionally NOT in this list:
// - regex_* (host PCRE2 hostcall), xml_*/yaml_*/markdown_* (compiled in),
// - unit_render()/component() (host resolver).
// W7d: every former native-only surface now goes through the membrane —
// zip_* (uce_host_zip), unit introspection (uce_host_units: unit_info/
// unit_call/units_list), regex/xml/yaml/markdown, filesystem, sqlite,
// background tasks, sleep, sockets/custom servers, memcache, mysql. No unit
// source token forces native anymore, so there is nothing left to scan for.
// (The native fallback now only covers cold/stale artifacts; W7e removes it.)
(void)source;
return(false);
}
static bool wasm_backend_native_fallback_needed(Request* context, const String& entry_unit)
{
if(!context || !context->server || entry_unit == "")
return(true);
// Cache the verdict per process, keyed on path + mtime: the source scan is
// otherwise a file read + 20 substring searches on every page request.
struct CachedVerdict { time_t mtime; bool fallback; };
static std::map<String, CachedVerdict> cache;
struct stat st;
time_t mtime = (stat(entry_unit.c_str(), &st) == 0) ? st.st_mtime : 0;
auto it = cache.find(entry_unit);
if(it != cache.end() && it->second.mtime == mtime)
return(it->second.fallback);
bool fallback = wasm_backend_native_fallback_uncached(context, entry_unit);
cache[entry_unit] = { mtime, fallback };
return(fallback);
}
// True if this request should be served by the wasm backend. Falls through to
// native when disabled, when init failed, or when the unit has no wasm artifact
// (e.g. units skip-listed for try/catch — automatic, graceful fallback). Mode-
// agnostic: the caller (page render / cli / serve_http) decides which entry to
// route here; this only gates on config, fallback tokens, artifact, and worker.
// True if this request should be served by the wasm backend. Every unit now
// runs on wasm (W7d retired the last native-only surfaces), so this only gates
// on config, the presence of a current wasm artifact, and a healthy worker —
// the remaining native fallback exists solely to cover a cold/stale artifact
// (a unit not yet compiled, or whose source is newer than its .wasm). W7e
// removes that last fallback once cold/stale triggers an on-demand wasm compile.
bool wasm_backend_should_handle(Request& request, const String& entry_unit)
{
if(!wasm_backend_configured(&request))
return(false);
if(wasm_backend_native_fallback_needed(&request, entry_unit))
return(false);
if(!wasm_artifact_exists(&request, entry_unit))
return(false);
if(wasm_backend_ensure_started(&request) != "")