Re: [Tarantool-patches] [PATCH luajit] Prevent sanitizer warning in os.time().

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

Hi, Sergey!
Thanks for the patch!
LGTM, with minor ignorable comments below.

On 05.06.26, Sergey Bronnikov wrote:
> From: Mike Pall <mike>
> 
> Reported by Sergey Bronnikov.
> 
> (cherry picked from commit 86d414f5cae062b06998ec66b0696a47d4f6a0f0)
> 
> The function `lj_cf_os_time()` calculates `tm_mon` and `tm_year`
> values using `get_field()` and when the helper function returns
> a negative value the resulted values may be negative as well. This
> is an undefined behaviour (signed integer overflow). The patch fixes
> that by adding a cast for the resulted value to returned by

Typo: s/to returned/to be returned/

> `get_field()`.

I am suggesting rephrasing this paragraph a bit to make it more clear:

| The function `lj_cf_os_time()` calculates the `tm_mon` and `tm_year`
| values using `get_field()`. If this helper function returns a negative
| result, subtraction may lead to undefined behavior due to signed integer
| overflow. The patch fixes the issue by adding a cast to the value
| returned by `get_field()`.

Feel free to ignore.

> 
> Sergey Bronnikov:
> * added the description and the test for the problem
> 
> Part of tarantool/tarantool#12480
> ---
> 
> Branch: https://github.com/tarantool/luajit/tree/ligurio/lj-1454-ub-os-time
> 
> Related issues:
> 
> * https://github.com/tarantool/tarantool/issues/12480
> * https://github.com/LuaJIT/LuaJIT/issues/1454
> 
>  src/lib_os.c                                  |  4 ++--
>  test/tarantool-tests/lj-1454-os-time.test.lua | 19 +++++++++++++++++++
>  2 files changed, 21 insertions(+), 2 deletions(-)
>  create mode 100644 test/tarantool-tests/lj-1454-os-time.test.lua
> 
> diff --git a/src/lib_os.c b/src/lib_os.c
> index ffbc3fdc..0feb0d47 100644
> --- a/src/lib_os.c
> +++ b/src/lib_os.c

<snipped>

> diff --git a/test/tarantool-tests/lj-1454-os-time.test.lua b/test/tarantool-tests/lj-1454-os-time.test.lua
> new file mode 100644
> index 00000000..2a48750c
> --- /dev/null
> +++ b/test/tarantool-tests/lj-1454-os-time.test.lua

I prefer the <lj-1454-ub-os-time.test.lua> name (as you named the
branch). Feel free to ignore.

> @@ -0,0 +1,19 @@
> +local tap = require('tap')
> +
> +-- The test file to demonstrate UBSan warning for `os.time()` with
> +-- a huge indices value for month and/or year.

s/a huge indices value/huge negative index values/

> +-- See also: https://github.com/LuaJIT/LuaJIT/issues/1454.
> +local test = tap.test('lj-1454-os-time')

I prefer the lj-1454-ub-os-time name (as you named the branch). Feel
free to ignore.

> +
> +test:plan(1)
> +
> +local INT_MIN = -2 ^ 31
> +
> +local cur_time = os.time({
> +  day = 1,
> +  month = INT_MIN,
> +  year = INT_MIN,
> +})
> +test:is(cur_time, nil, 'os.time() with INT_MIN')
> +
> +test:done(true)
> -- 
> 2.43.0
> 

-- 
Best regards,
Sergey Kaplun