Re: Restartable Sequences system call merged into Linux

From: Florian Weimer
Date: Tue Jun 12 2018 - 09:11:45 EST

On 06/11/2018 10:04 PM, Mathieu Desnoyers wrote:
----- 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
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

Looks I was mistaken and this is very similar to the robust mutex list.

Should we treat it the same way? Always allocate it for each new thread and register it with the kernel?

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

Then the user code needs just the address of the structure.

How much coordination is needed between different users of this interface? Looking at the the section hacks, I don't think we want to put this into glibc at this stage. It looks more like something for which we traditionally require compiler support.