[<prev] [next>] [<thread-prev] [day] [month] [year] [list]
Message-ID: <CAH9TF6NXM3WFfR_R9epFVwKeG+j+QEg1fAb_h90bcZ2gXVTmAg@mail.gmail.com>
Date: Fri, 13 Dec 2024 20:04:22 +0100
From: Alex Rønne Petersen <alex@...xrp.com>
To: Rich Felker <dalias@...c.org>
Cc: Fangrui Song <i@...kray.me>, musl@...ts.openwall.com,
Alexander Monakov <amonakov@...ras.ru>
Subject: Re: [PATCH] s390x: Mark __tls_get_addr hidden before invoking it.
On Fri, Dec 13, 2024 at 12:18 PM Rich Felker <dalias@...c.org> wrote:
>
> On Thu, Dec 12, 2024 at 06:45:39PM +0100, Alex Rønne Petersen wrote:
> > On Sat, Nov 30, 2024 at 6:51 PM Fangrui Song <i@...kray.me> wrote:
> > > (I am not versed in s390x assembly, but I have some notes about __tls_get_offset
> > >
> > > https://maskray.me/blog/2024-02-11-toolchain-notes-on-z-architecture#general-dynamic-tls-model
> > >
> > > The 32-bit ABI had to use __tls_get_offset because some nice
> > > general-instructions-extension was unavailable when the ABI was
> > > codified.
> > > The 64-bit ABI following the 32-bit __tls_get_offset was just unfortunate..
> >
> > From your notes, it sounds like __tls_get_addr has to be hidden, even
> > if we don't actually make use of it in __tls_get_offset. Is my
> > understanding correct?
> >
> > If yes, what would be the preferred way to achieve this in musl?
>
> There is no requirement for a symbol to be hidden unless it violates
> namespace, which is not the case here. The problem is that the code in
> __tls_get_offset is performing a call to __tls_get_addr in a manner
> that's not valid unless the call target is local.
>
> My preferred fix would be getting rid of the call and inlining
> __tls_get_addr into __tls_get_offset. This was not possible back when
> the port was added because __tls_get_addr had a complex code path for
> installing new TLS on first-access. That was changed long ago, so now
> it's a fairly trivial instruction sequence.
Before I send a patch, just to confirm, is this what you have in mind?
.global __tls_get_offset
.type __tls_get_offset,%function
__tls_get_offset:
stmg %r14, %r15, 112(%r15)
aghi %r15, -160
ear %r0, %a0
sllg %r0, %r0, 32
ear %r0, %a1
la %r1, 0(%r2, %r12)
lg %r3, 0(%r1)
sllg %r4, %r3, 3
lg %r5, 8(%r0)
lg %r2, 0(%r4, %r5)
ag %r2, 8(%r1)
sgr %r2, %r0
lmg %r14, %r15, 272(%r15)
br %r14
Powered by blists - more mailing lists
Confused about mailing lists and their use?
Read about mailing lists on Wikipedia
and check out these
guidelines on proper formatting of your messages.
