Re: [Tarantool-patches] [PATCH luajit v2] Throw any errors before stack changes in trace stitching.

[Sergey Kaplun via Tarantool-patches <tarantool-patches@dev.tarantool.org>]

Hi, Maxim!
Thanks for the fixes!
LGTM, after fixing the comments below.

On 01.03.24, Maxim Kokryashkin wrote:
> From: Mike Pall <mike>
> 
> Thanks to doujiang24.
> 
> (cherry-picked from commit 3f9389edc6cdf3f78a6896d550c236860aed62b2)
> 
> The Lua stack is changed in the `recff_stitch`, so if the trace
> is aborted, for example, when the `maxsnap` is reached, and an
> error is thrown from there, the execution continues with an
> unbalanced stack.
> 
> This patch adds a check for snapshot overflow to the
> `recff_stitch` to overcome the issue for the `LJ_TRERR_SNAPOV`
> case, but other cases remain unresolved and should be fixed in
> other series. For a detailed description of the remaining cases,
> see the issue[1].
> 
> [1]: https://github.com/LuaJIT/LuaJIT/issues/1166

I suppose it is better to drop the link (or just mention it in the test)
to avoid excess notification in the upstream repository.

> 
> Maxim Kokryashkin:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#9595
> ---
> Changes in v2:
> - Fixed comments as per review by Sergey Kaplun
> 
> Branch: https://github.com/tarantool/luajit/tree/fckxorg/lj-720-errors-before-stitch
> 
>  src/lj_ffrecord.c                             |  4 ++++
>  .../lj-720-errors-before-stitch.test.lua      | 20 +++++++++++++++++++
>  2 files changed, 24 insertions(+)
>  create mode 100644 test/tarantool-tests/lj-720-errors-before-stitch.test.lua
> 
> diff --git a/src/lj_ffrecord.c b/src/lj_ffrecord.c
> index 1b2ddb72..e3ed80fb 100644
> --- a/src/lj_ffrecord.c
> +++ b/src/lj_ffrecord.c

<snipped>

> diff --git a/test/tarantool-tests/lj-720-errors-before-stitch.test.lua b/test/tarantool-tests/lj-720-errors-before-stitch.test.lua
> new file mode 100644
> index 00000000..00fb0b9b
> --- /dev/null
> +++ b/test/tarantool-tests/lj-720-errors-before-stitch.test.lua
> @@ -0,0 +1,20 @@
> +local tap = require('tap')
> +local test = tap.test('lj-720-errors-before-stitch'):skipcond({
> +  ['Test requires JIT enabled'] = not jit.status(),
> +})
> +test:plan(1)
> +
> +-- `math.modf` recording is NYI.
> +local modf = math.modf

Why do we need to the use local value here?

> +jit.opt.start('hotloop=1', 'maxsnap=1')
> +
> +-- The loop has only two iterations: the first to detect its
> +-- hotness and the second to record it. The snapshot limit is
> +-- set to one and is certainly reached.
> +for _ = 1, 2 do
> +  -- Forcify stitch.
> +  modf(1.2)
> +end
> +
> +test:ok(true, 'stack is balanced')
> +test:done(true)
> --
> 2.43.0
> 

-- 
Best regards,
Sergey Kaplun