Re: A collection of LD_AUDIT bugs that are important for tools (with better formatting for this list)

[John Mellor-Crummey via Libc-alpha <libc-alpha@sourceware.org>]

Florian,


> On Jun 22, 2021, at 10:36 AM, Florian Weimer <fweimer@redhat.com> wrote:
> 
> * John Mellor-Crummey:
> 
>>> On Jun 22, 2021, at 3:15 AM, Florian Weimer <fweimer@redhat.com> wrote:
>>> You can already see this non-interceptable thread creation behavior
>>> today (in glibc 2.33 and earlier) with thrd_create, which does not
>>> result in a pthread_create call, either, despite creating a new thread
>>> as if by pthread_create.
>> 
>> Having a non-interposable thrd_create is a problem for us too, though 
>> we haven’t yet seen it in practice in HPC applications (or maybe it happened
>> and we were just unaware!).
> 
> I meant that thrd_create needs to be intercepted separately.  This will
> still work.

Got it.

Would you recommend intercepting clone instead of trying
to intercept pthread_create and thrd_create?

That should avoid trouble interposing pthread_create.

> 
>>> Going back to trheading, I find it a bit curious that you intercept
>>> pthread_create, but not pthread_join.  How do you detect thread exit?  I
>>> assume you are interested in that event, too.  Merely wrapping the
>>> thread start routine is insufficient because there are other ways for a
>>> thread to exit besides returning from the start routine and calling
>>> pthread_exit (e.g., thread cancellation and unwinding).
>> 
>> We use pthread_cleanup_push to add a routine that will be called when a thread
>> exits.
> 
> Okay, that should work, although some application-supplied TLS
> destructors will run later than that.

For our tools, we need to shut down profiling when a thread is finishing. That
can and should be done before the thread really gets torn down. We have
learned the hard way that we need to turn off profiling before TLS destruction starts. 

--
John Mellor-Crummey		Professor
Dept of Computer Science	Rice University
email: johnmc@rice.edu		phone: 713-348-5179