Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10)

[Mathieu Desnoyers <mathieu.desnoyers@efficios.com>]

----- On Jun 12, 2019, at 4:00 PM, Mathieu Desnoyers mathieu.desnoyers@efficios.com wrote:

> ----- On Jun 10, 2019, at 4:43 PM, carlos carlos@redhat.com wrote:
> 
>> On 6/6/19 7:57 AM, Florian Weimer wrote:
>>> Let me ask the key question again: Does it matter if code observes the
>>> rseq area first without kernel support, and then with kernel support?
>>> If we don't expect any problems immediately, we do not need to worry
>>> much about the constructor ordering right now.  I expect that over time,
>>> fixing this properly will become easier.
>> 
>> I just wanted to chime in and say that splitting this into:
>> 
>> * Ownership (__rseq_handled)
>> 
>> * Initialization (__rseq_abi)
>> 
>> Makes sense to me.
>> 
>> I agree we need an answer to this question of ownership but not yet
>> initialized, to owned and initialized.
>> 
>> I like the idea of having __rseq_handled in ld.so.
> 
> Very good, so I'll implement this approach. Sorry for the delayed
> feedback, I am traveling this week.

I had issues with cases where application or LD_PRELOAD library also
define the __rseq_handled symbol. They appear not to see the same
address as the one initialized by ld.so.

I tried using the GL() macro in ld.so to set __rseq_handled, but it's
the wrong address compared to what the preload lib and application observe.

Any thoughts on how to solve this ?

Thanks,

Mathieu

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