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Message-ID: <20260619012009.GS3520958@port70.net>
Date: Fri, 19 Jun 2026 03:20:09 +0200
From: Szabolcs Nagy <nsz@...t70.net>
To: Rich Felker <dalias@...c.org>
Cc: musl@...ts.openwall.com
Subject: Re: [PATCH] or1k: fix local-exec tls with large alignment
* Rich Felker <dalias@...c.org> [2026-06-18 20:15:25 -0400]:
> On Fri, Jun 19, 2026 at 01:40:49AM +0200, Szabolcs Nagy wrote:
> > * Rich Felker <dalias@...c.org> [2026-06-18 17:58:29 -0400]:
> > > On Thu, Jun 18, 2026 at 09:12:56PM +0200, Szabolcs Nagy wrote:
> > > > or1k uses an unusual variant of the TLS_ABOVE_TP layout:
> > > >
> > > > powerpc, mips, m68k:
> > > > pthread | tls
> > > > +----------+-----------------+--
> > > > | |< tpoff >|
> > > > self a = e = m tp
> > > >
> > > > arm, aarch64, sh:
> > > > pthread < gap >| tls
> > > > +----------+-------------+------
> > > > | | |
> > > > self a = e = tp m
> > > >
> > > > or1k:
> > > > pthread < gap >| tls
> > > > +----------+-------------+------
> > > > | |< tpoff >|
> > > > self a = e m = tp
> > >
> > > To be sure we understand this correctly, can you draw a diagram like
> > > this for the wrong way we have the or1k layout now?
> >
> > i can resend the patch, but it's just:
>
> No need, I just wanted to see it to make sure I understand what you
> meant.
>
> > or1k old:
> > pthread | tls
> > +----------+--------------------
> > | |
> > self a = e = m = tp
> >
> > or1k fixed:
> > pthread < gap >| tls
> > +----------+-------------+------
> > | |< tpoff >|
> > self a = e m = tp
>
> OK, so it's essentially the tp being aligned to something nonzero mod
> tls_align. That would be an alternate way to implement it (adding
> support the the arch to declare the desired residue), though as long
> as we can just do it with a GAP_ABOVE_TP, that seems ok.
>
> But are you sure this is correct setting TPOFF_K to cancel the
> GAP_ABOVE_TP? TPOFF_K affects all modules not just the main program. I
> don't see how changing it doesn't break initial-exec accesses to TLS
> in libraries.
i wrote some tests now, it all looks good.
with diagram:
pthread < gap >| tls |tlsvar
+----------+-------------+-------+--+-----
| |< tpoff >| |
self a = e m = tp modtls
ie access:
tlsvar_addr = tp + *reloc
ldso:
*reloc = tlsvar_offset + modtls_offset + TPOFF_K
where
tlsvar_offset = tlsvar - modtls
modtls_offset = modtls - a
TPOFF_K = -tpoff = a - tp
so
tlsvar_addr = tp + (tlsvar - tp)
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