Re: Restartable Sequences system call merged into Linux

[Mathieu Desnoyers]

----- On Jun 11, 2018, at 3:55 PM, Florian Weimer fweimer@xxxxxxxxxx wrote:

> On 06/11/2018 09:49 PM, Mathieu Desnoyers wrote:
>> It should be noted that there can be only one rseq TLS area registered per
>> thread,
>> which can then be used by many libraries and by the executable, so this is a
>> process-wide (per-thread) resource that we need to manage carefully.
> 
> Is it possible to resize the area after thread creation, perhaps even
> from other threads?

I'm not sure why we would want to resize it. The per-thread area is fixed-size.
Its layout is here: include/uapi/linux/rseq.h: struct rseq

The ABI is designed so that all users (program and libraries) can interact
through this per-thread TLS area.

> 
> If there is only one contiguous area, this generally means there needs
> to be linker support, similar to what we have for initial-exec TLS today.

Not entirely sure what you imply by "one contiguous area". All we need is
a single fixed-size TLS area for each thread.

Thanks,

Mathieu

> 
> Thanks,
> Florian

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