Re: [Tarantool-patches] [PATCH luajit 1/2] build: introduce LUAJIT_USE_UBSAN option

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

Hi, Sergey!
Thanks for the reply!

On 20.06.24, Sergey Bronnikov wrote:
> Hi, Sergey,
> 
> On 16.05.2024 13:14, Sergey Kaplun wrote:
> > Hi, folks!
> > Some more thoughts below.
> >
> > On 15.05.24, Sergey Kaplun wrote:
> >
> > <snipped>
> >
> >> +  string(JOIN "," UBSAN_IGNORE_OPTIONS
> >> +    # Misaligned pseudo-pointers are used to determine internal
> >> +    # variable names inside the `for` cycle.
> >> +    alignment
> >> +    # Not interested in float cast overflow errors.
> >> +    float-cast-overflow
> >> +    # NULL checking is disabled because this is not a UB and
> >> +    # raises lots of false-positive fails.
> >> +    null
> > Maybe it is worth to add also "nonnull-attribute" to the ignore options:
> >
> > ```
> > LSAN_OPTIONS="abort_on_error=1" src/luajit -e 'error("bad usage", 3)'
> > /home/burii/builds_workspace/luajit/gh-8473-ubsan/src/lj_buf.h:75:25: runtime error: null pointer passed as argument 1, which is declared to never be null
> > /usr/include/string.h:44:28: note: nonnull attribute specified here
> > ```
> >
> > Here, `memcpy()` gets the NULL pointer as the first argument and the
> > `len` == 0. So there are no problems here. Also, the nullability
> > violation is not a UB, as mentioned in the documentation.
> >
> > Thoughts?
> 
> I agree with arguments provided by Maxim - it's UB, the standard states 
> it clearly,
> 
> and it should be fixed. I propose to do the following:
> 
> - suppress the check (add it to UBSAN_IGNORE_OPTIONS) with appropriate 
> comment
> 
> (something like "we know it is bad, but it is unfixed in upstream, we 
> will wait a fix").
> 
> Probably we should suppress it per file like you did with other checks.

I suppress this particular failure inline, like for other checks.
Should I add the test for it?

> 
> - send a fix to upstream or submit an issue to the upstream (I'll not 
> insist, but it would be desirable)

I suppose this issue will be marked as won't fix or invalid. Feel free
to submit the ticket if you want.

> 
> >

<snipped>

> >> +  )

-- 
Best regards,
Sergey Kaplun