Re: [Tarantool-patches] [PATCH luajit] Fix compilation of getmetatable() for UDTYPE_IO_FILE

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

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Hi, Sergey,

please see below.

Updated version has been force-pushed.

Sergey

On 12.11.2024 22:23, Sergey Kaplun wrote:
> Hi, Sergey!
> Thanks for the patch!
> Nice catch!
>
> Please, consider my comments below.
>
> On 07.11.24, Sergey Bronnikov wrote:
>> From: Sergey Bronnikov<sergeyb@tarantool.org>
>>
>> The patch fixes a problem with recording `getmetatable()`
>> for I/O object: recording of `getmetatable` call with a file
> Typo: s<I/O><an I/O>
> Typo: s/recording of/recording the/
> Typo: s/a file/file/
Fixed.
>
>> descriptors represented by userdata object `UDTYPE_IO_FILE`
>> (like `io.stdout`) leads to violation of assertion in
>> `rec_check_slots`.
> Nit:
> | ... by the userdata object `UDTYPE_IO_FILE` (like `io.stdout`) always
> | stores `nil` instead of the given metatable. This leads to the
> | violation of the assertion in `rec_check_slots`.
>
>> Note, the problem was fixed upstream in different manner, see
>> commit 5141cbc20c43
> Nit: Please, use full commit hash.

Fixed, but usually ten characters is enough [1]:

 > Generally, eight to ten characters are more than enough to be unique 
within a project. For example, as of February 2019, the Linux kernel 
(which is a fairly sizable project) has over 875,000 commits and almost 
seven million objects in its object database, with no two objects whose 
SHA-1s are identical in the first 12 characters.

1. https://git-scm.com/book/en/v2/Git-Tools-Revision-Selection

> Also, please describe that specialized recording (introduced in the
> upstream) lacks the check of the metatable precense. So, the fix in
> upstream is incomplete (according to the comment [1]).

Added:


     Note, the problem was fixed upstream in different manner, see
     commit 5141cbc20c43921778ff36be541c15888bee8ee3
     ("Fix compiliation of getmetatable() for UDTYPE_IO_FILE.").
     Note, the specialization omits the check of `__metatable` field
     precense and the check for the metatable itself. So, if we change
     the metatable on the object after the trace is compiled, the trace
     becomes invalid. The proposed test demonstrates these cases as
     well.

>
> Also, please add both testcases from the issue comment [1] (don't forget
> to restore metatable after the first of them).
Added.
>> ("Fix compiliation of getmetatable() for UDTYPE_IO_FILE.").
>> ---
>>   src/lj_record.c                               |  2 +-
>>   ...-incorrect-recording-getmetatable.test.lua | 21 +++++++++++++++++++
>>   2 files changed, 22 insertions(+), 1 deletion(-)
>>   create mode 100644 test/tarantool-tests/lj-1279-incorrect-recording-getmetatable.test.lua
>>
>> diff --git a/src/lj_record.c b/src/lj_record.c
>> index cc97bdf9..7181b72a 100644
>> --- a/src/lj_record.c
>> +++ b/src/lj_record.c
> <snipped>
>
>> diff --git a/test/tarantool-tests/lj-1279-incorrect-recording-getmetatable.test.lua b/test/tarantool-tests/lj-1279-incorrect-recording-getmetatable.test.lua
>> new file mode 100644
>> index 00000000..8bf22ca7
>> --- /dev/null
>> +++ b/test/tarantool-tests/lj-1279-incorrect-recording-getmetatable.test.lua
>> @@ -0,0 +1,21 @@
>> +local tap = require('tap')
>> +
>> +local test = tap.test('lj-1279-incorrect-recording-getmetatable')
>> +test:plan(1)
>> +
>> +-- A test file to demonstrate an incorrect recording of
>> +-- getmetatable() for I/O handlers.
>> +--https://github.com/LuaJIT/LuaJIT/issues/1279
> Nit: Usually the link is right before `tap.test()` declaration.
Fixed.
>
>> +
>> +jit.opt.start("hotloop=1")
> Nit: Please use single quotes.
Fixed.
>
>> +
>> +local obj = io.stdout
> Minor: I would rather name the variable like the corresponding type --
> `ud_io_file`. Feel free to ignore.

Fixed.


>
>> +local getmetatable = getmetatable
>> +
>> +for _ = 1, 4 do
>> +  _ = getmetatable(obj)
>> +end
>> +
>> +test:ok(true, 'getmetatable() recording is correct')
> Let's check the resulted metatable too. (We can use `test:samevalues()`
> here, for example.)
Fixed.
>
>> +
>> +test:done(true)
>> -- 
>> 2.34.1
>>
> [1]:https://github.com/LuaJIT/LuaJIT/issues/1279#issuecomment-2382392847
>

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