Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10)
From: Mathieu Desnoyers
Date: Fri Jun 14 2019 - 10:03:53 EST
----- On Jun 14, 2019, at 3:53 PM, Florian Weimer fweimer@xxxxxxxxxx wrote:
> * Mathieu Desnoyers:
>> ----- On Jun 14, 2019, at 3:42 PM, Florian Weimer fweimer@xxxxxxxxxx wrote:
>>> * Mathieu Desnoyers:
>>>> + /* Publicize rseq registration ownership. This must be performed
>>>> + after rtld re-relocation, before invoking constructors of
>>>> + preloaded libraries. */
>>>> + rseq_init ();
>>> Please add a comment that IFUNC resolvers do not see the initialized
>>> value. I think this is okay because we currently do not support access
>>> to extern variables in IFUNC resolvers.
>> Do IFUNC resolvers happen to observe the __rseq_handled address that
>> was internal to ld.so ?
> They should observe the correct address, but they can access the
> variable before initialization. An initializer in ld.so will not have
> an effect if an interposed definition initalized the variable to
> something else.
>> If so, we could simply initialize __rseq_handled twice: early before calling
>> IFUNC resolvers, and after ld.so re-relocation.
> No, I don't think this will make a difference.
So comment it is:
/* Publicize rseq registration ownership. This must be performed
after rtld re-relocation, before invoking constructors of
preloaded libraries. IFUNC resolvers are called before this
initialization, so they may not observe the initialized state. */