Re: GNU libc support for extensible rseq ABI

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

On 2023-05-18 14:06, Florian Weimer wrote:
> * Mathieu Desnoyers:
> 
>> Hi Carlos, Florian,
>>
>> Now that the 6.3 Linux kernel is out, the ABI for extensible rseq is
>> frozen, and we could add support for it in glibc. It would be good to
>> upstream this support before we run out of room in the padding space we
>> currently re-use.
>>
>> What glibc release should we target for this ?
> 
> It may be possible to hack this into the existing TLS allocator.  See
> the loop in _dl_determine_tlsoffset.  It should be possible to add the
> rseq area as another static TLS block (perhaps as the first one before
> the loop), with the size and alignment requested by the kernel.  If we
> can make that work, it's going to be a fairly small patch that should
> be backportable as well.  That could go into 2.38 or 2.39.
> 
> If we need a new TLS allocator, it's definitely 2.39 material at this
> point, potentially later.

Michael (in CC) showed interest in working on this. I'm adding him to 
this e-mail thread so you are both aware of each other's ongoing progress.

Thanks,

Mathieu

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