Re: [PATCH 1/5] glibc: Perform rseq(2) registration at C startup and thread creation (v10)
From: Mathieu Desnoyers
Date: Wed Jun 12 2019 - 10:20:41 EST
----- On Jun 6, 2019, at 1:57 PM, Florian Weimer fweimer@xxxxxxxxxx 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.
> 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.