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Date:   Wed, 12 Jun 2019 10:16:02 -0400 (EDT)
From:   Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To:     Florian Weimer <fweimer@redhat.com>
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        Rich Felker <dalias@libc.org>,
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Subject: Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup
 and thread creation (v10)
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Thread-Topic: glibc: Perform rseq(2) registration at C startup and thread creation (v10)
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----- On Jun 6, 2019, at 1:57 PM, Florian Weimer fweimer@redhat.com wrote:

> * Mathieu Desnoyers:
> 
[...]
> 
>>> The final remaining case is static dlopen.  There is a copy of ld.so on
>>> the dynamic side, but it is completely inactive and has never run.  I do
>>> not think we need to support that because multi-threading does not work
>>> reliably in this scenario, either.  However, we should skip rseq
>>> registration in a nested libc (see the rtld_active function).
>>
>> So for SHARED, if (!rtld_active ()), we should indeed leave the state of
>> __rseq_handled as it is, because we are within a nested inactive ld.so.
> 
> I think we should add __rseq_handled initialization to ld.so, so it will
> only run once, ever.

OK

> 
> It's the registration from libc.so which needs some care.  In
> particular, we must not override an existing registration.

OK, so it could check if __rseq_abi.cpu_id is -1, and only
perform registration if it is the case. Or do you have another
approach in mind ?

For the main thread, "nested" unregistration does not appear to be a
problem, because we rely on program exit() to implicitly unregister.

Thanks,

Mathieu

> 
> Thanks,
> Florian

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com