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	Thu, 18 May 2023 20:06:44 +0200
From: Florian Weimer <fw@deneb.enyo.de>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: "carlos@redhat.com" <carlos@redhat.com>,  libc-alpha
 <libc-alpha@sourceware.org>
Subject: Re: GNU libc support for extensible rseq ABI
References: <e7dc7199-0b19-94ed-c764-12c07a447bb6@efficios.com>
Date: Thu, 18 May 2023 20:06:44 +0200
In-Reply-To: <e7dc7199-0b19-94ed-c764-12c07a447bb6@efficios.com> (Mathieu
	Desnoyers's message of "Thu, 18 May 2023 13:48:18 -0400")
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* 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.