#!/usr/bin/env tarantool
-- Trace-stability gate (PLAN.md M6).
--
-- For each hot encode/decode path, run a few thousand iterations with
-- a `trace` listener attached and assert that no trace aborts in
-- `runtime/pb/*` or `examples/expected/**/*_pb.lua` fall into the
-- "fatal" set — bytecodes/builtins LuaJIT can't compile, blacklists,
-- persistent type instability. Benign aborts (loop boundaries, retry
-- recording, short warmup traces) are ignored; they are normal JIT
-- bookkeeping and don't mean the hot path fell off the JIT.
--
-- Scope: `pairs()` over a hash compiles to bytecode ISNEXT, which is
-- NYI in the LuaJIT 2.1 fork Tarantool ships. That makes map-field
-- encode/decode (the only place we use `pairs` in the hot path)
-- inherently un-stay-on-trace. The last scenario pins that limitation
-- so we notice if upstream ever lifts it.
--
-- Run as a standalone tarantool script — not via luatest. On macOS
-- arm64, luatest's framework load fills the JIT mcode arena before
-- tests run, so traces in the test body fail with "failed to allocate
-- mcode memory" rather than the real reason we're trying to measure.
--
-- Usage:
-- tarantool bench/jit_trace.lua
-- exit 0 = all checks passed; non-zero = a fatal abort was hit or a
-- hot path failed to compile at all.
package.path = './runtime/?.lua;./runtime/?/init.lua;'
.. './examples/expected/?.lua;./examples/expected/?/init.lua;'
.. package.path
jit.on()
local vmdef = require('jit.vmdef')
-- Codes from jit.vmdef.traceerr (1-indexed). We treat these as fatal —
-- they mean the JIT genuinely cannot compile the path, not that it's
-- reorganizing traces. See vmdef.traceerr for the full list.
local FATAL = {
[5] = true, -- blacklisted
[7] = true, -- NYI: bytecode %s
[11] = true, -- bad argument type
[15] = true, -- NYI: unsupported variant of FastFunc %s
[16] = true, -- NYI: return to lower frame
[18] = true, -- missing metamethod
[19] = true, -- looping index lookup
[20] = true, -- NYI: mixed sparse/dense table
[22] = true, -- NYI: unsupported C type conversion
[23] = true, -- NYI: unsupported C function type
[26] = true, -- persistent type instability
}
local function is_our_code(src)
if type(src) ~= 'string' then return false end
return src:match('runtime/pb/') ~= nil
or src:match('examples/expected/') ~= nil
end
local function fmt_reason(code, info)
local msg = vmdef.traceerr[code] or ('?code=' .. tostring(code))
return (msg:gsub('%%s', tostring(info or '?')))
end
local jutil = require('jit.util')
local function record(fn, warmup_iters, measured_iters)
for _ = 1, warmup_iters do fn() end
jit.flush()
local fatal, stops = {}, 0
local start_loc, stop_loc = {}, {} -- trace_no -> {src, line, pc, parent}
local cb = function(what, tr, func, pc, code, info)
if what == 'start' and func then
local di = debug.getinfo(func, 'S')
-- For side traces: `code` is the parent trace number,
-- `info` is the parent's exit index. Root traces have code=nil.
start_loc[tr] = {
src = di.short_src, line = di.linedefined, pc = pc,
parent = code, -- nil for root, traceno for side trace
}
elseif what == 'stop' then
stops = stops + 1
if func then
local di = debug.getinfo(func, 'S')
stop_loc[tr] = {src = di.short_src, line = di.linedefined}
end
elseif what == 'abort' and FATAL[code] then
local di = func and debug.getinfo(func, 'S') or {short_src = '?'}
if is_our_code(di.short_src) then
fatal[#fatal + 1] = {
src = di.short_src,
line = di.linedefined,
code = code,
info = info,
}
end
end
end
jit.attach(cb, 'trace')
for _ = 1, measured_iters do fn() end
jit.attach(cb)
-- A "bridge" we care about is a SIDE trace (i.e. a child compiled off
-- a guard exit of some parent trace) whose own natural exit drops to
-- the interpreter. Pattern: parent runs hot → guard fails → side
-- trace covers the divergent code → falls back to VM dispatch instead
-- of stitching to another trace. Each such bridge costs a few hundred
-- ns of interp dispatch on every hot iteration.
--
-- Pure root traces that end in linktype=interpreter are NOT bridges:
-- they're short JIT'd snippets entered from interpreter and exit back
-- to it, with no extra dispatch cost beyond normal interp execution
-- of the surrounding code.
local bridges = {}
for tr = 1, 1024 do
local info = jutil.traceinfo(tr)
if not info then break end
if info.linktype == 'interpreter' and info.link == 0 then
local s = start_loc[tr] or stop_loc[tr]
if s and is_our_code(s.src) and s.parent then
bridges[#bridges + 1] = {
tr = tr,
src = s.src,
line = s.line,
pc = s.pc,
parent = s.parent,
}
end
end
end
return fatal, stops, bridges
end
local failures = 0
local checks = 0
local function check(label, fn, opts)
opts = opts or {}
local fatal, stops, bridges = record(fn, 2000, 5000)
checks = checks + 1
if #fatal > 0 and not opts.expect_fatal_in then
failures = failures + 1
io.stderr:write(string.format(
' [FAIL] %s — %d fatal abort(s) in our code:\n', label, #fatal))
local seen = {}
for _, a in ipairs(fatal) do
local k = a.src .. ':' .. a.line .. '|' .. a.code
if not seen[k] then
seen[k] = true
io.stderr:write(string.format(
' %s:%d %s\n',
a.src, a.line, fmt_reason(a.code, a.info)))
end
end
return
end
if opts.expect_fatal_in then
local saw = false
for _, a in ipairs(fatal) do
if a.src:match(opts.expect_fatal_in) then saw = true; break end
end
if not saw then
failures = failures + 1
io.stderr:write(string.format(
' [FAIL] %s — expected a fatal abort in %q (known limitation), got none\n',
label, opts.expect_fatal_in))
return
end
io.stderr:write(string.format(
' [PIN ] %s — expected NYI present (known LuaJIT 2.1 limitation)\n',
label))
return
end
if stops == 0 then
failures = failures + 1
io.stderr:write(string.format(
' [FAIL] %s — no trace was compiled (stops=0)\n', label))
return
end
-- Interpreter bridges (side trace -> interp) are real but their
-- compilation timing is non-deterministic — across 10 runs you'll
-- see 0–4 in decoder paths (parent trace bakes in the 1-byte varint
-- fast path, the multi-byte side trace can't self-loop). They're a
-- topology metric, not a pass/fail signal — report them for
-- visibility, don't fail the gate.
io.stderr:write(string.format(
' [ OK ] %s (stops=%d, bridges=%d)\n', label, stops, #bridges))
if #bridges > 0 then
for _, b in ipairs(bridges) do
io.stderr:write(string.format(
' info: bridge tr%d side-of tr%s %s:%d pc=%s\n',
b.tr, tostring(b.parent), b.src, b.line, tostring(b.pc)))
end
end
end
-- ---------------------------------------------------------------------------
io.stderr:write('tarantool-protobuf trace-stability gate ('
.. (jit.version or '?') .. ')\n')
for _, mode in ipairs({'full', 'runtime'}) do
local hello = require(mode .. '.hello.hello_pb')
local addr = {street = '1 Main St', city = 'Springfield', zip = 12345}
local addr_bytes = hello.Address_encode(addr)
-- Person with repeated string, packed int32, nested message — no
-- map fields (see top-of-file scope note).
local person = {
name = 'bigbes', age = 42,
address = addr,
lucky_numbers = {7, 13, 21, 42, 99, 144, 233, 377},
emails = {'a@b.c', 'd@e.f', 'g@h.i', 'j@k.l'},
status = hello.Status.OK,
}
local person_bytes = hello.Person_encode(person)
local result = {value = 'ok'}
local result_bytes = hello.Result_encode(result)
check(mode .. '/Address_encode',
function() hello.Address_encode(addr) end)
check(mode .. '/Address_decode',
function() hello.Address_decode(addr_bytes) end)
check(mode .. '/Person_encode',
function() hello.Person_encode(person) end)
check(mode .. '/Person_decode',
function() hello.Person_decode(person_bytes) end)
check(mode .. '/Result_encode (oneof)',
function() hello.Result_encode(result) end)
check(mode .. '/Result_decode (oneof)',
function() hello.Result_decode(result_bytes) end)
-- Lazy hot paths: index build, sparse :get, untouched :encode
-- (passthrough). The mutation/encode path (:set + :encode walking
-- dirty fields) is not gated — it's expected to be slower-and-pairs,
-- not a tight inner loop. Passthrough is what we promised to stay
-- on trace, since untouched :encode just returns _bytes verbatim.
check(mode .. '/Person_decode_lazy (index pass)',
function() hello.Person_decode_lazy(person_bytes) end)
check(mode .. '/Person_decode_lazy + :get x2',
function()
local v = hello.Person_decode_lazy(person_bytes)
local _ = v:get('name'); local _2 = v:get('age')
end)
check(mode .. '/Person_decode_lazy + :encode (passthrough)',
function()
local _ = hello.Person_decode_lazy(person_bytes):encode()
end)
-- Multi-byte varint paths. The default Person fixture has all 1-byte
-- varints (field IDs 1-15, lengths < 128, packed-int values < 128),
-- so it only exercises encode_varint's fast path / decode_int32's
-- inlined 1-byte branch. This fixture forces the 2/3-byte paths:
-- * `name` is a 200-byte string → 2-byte LEN prefix, exercises
-- encode_varint_slow's 2-byte branch and decode_string's
-- 2-byte LEN fallback.
-- * `lucky_numbers` carry multi-byte values → packed payload is
-- varint-of-varints all hitting the slow path.
-- If these regress (e.g. encode_varint_slow grows past inline budget
-- and parent traces stop inlining it), the gate fires.
local big_person = {
name = string.rep('x', 200),
age = 42,
lucky_numbers = {150, 200, 1000, 20000, 50000, 100000, 200000, 500000},
}
local big_person_bytes = hello.Person_encode(big_person)
check(mode .. '/Person_encode multi-byte varint',
function() hello.Person_encode(big_person) end)
check(mode .. '/Person_decode multi-byte varint',
function() hello.Person_decode(big_person_bytes) end)
end
-- Pin the known map limitation: pairs() over a hash compiles to bytecode
-- ISNEXT, which Tarantool LuaJIT 2.1 can't trace. If this stops triggering,
-- upstream lifted the restriction and our scope claim can broaden.
do
local hello = require('full.hello.hello_pb')
local with_map = {
name = 'bigbes', age = 42,
ages_by_nickname = {bigbes = 1, eb = 2, blikh = 3},
}
check('full/Person_encode with map (known NYI)',
function() hello.Person_encode(with_map) end,
{expect_fatal_in = 'hello_pb%.lua'})
end
io.stderr:write(string.format(
'\n%d/%d checks passed\n', checks - failures, checks))
os.exit(failures > 0 and 1 or 0)