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Date: Sat, 25 Jun 2022 11:48:10 +0200
From: Szabolcs Nagy <nsz@port70.net>
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Subject: Re: [musl] Fwd: mesa | Remove USE_ELF_TLS macro (!17213)

* =E7=BD=97=E5=8B=87=E5=88=9A(Yonggang Luo) <luoyonggang@gmail.com> [2022-0=
6-25 13:25:31 +0800]:
> On Sat, Jun 25, 2022 at 12:47 PM Markus Wichmann <nullplan@gmx.net> wrote:
> >
> > On Sat, Jun 25, 2022 at 11:36:09AM +0800, =E7=BD=97=E5=8B=87=E5=88=9A(Y=
onggang Luo) wrote:
> > > So I am confused. What's the situation about ELF-TLS support in musl?
> > > Is that still broken now?
> >
> > musl has always supported ELF-TLS anywhere except in libc itself. That
> > was also never the problem. The problem was that the mesa people select
> > the initial-exec TLS model explicitly, even though libGL ends up being
> > dlopen()ed quite often, and then you should be using the general-dynamic
> > model instead.
>=20
> My question is does musl support ELS-TLS when using dl-open.
>=20

musl supports ELF TLS with or without dlopen.

if something crashes that's most likely a bug in mesa.

>=20
> >
> > According to [1], Rich proposed dropping the initial-exec attribute and
> > replacing it with -mtls-dialect=3Dgnu2 eight years ago. Has that happen=
ed
> > yet? If so, dlopen()ing libGL with musl ought to work.
>=20
> `initial-exec` are only specified for  __GLIBC__, If musl  not predefined
> macro ` __GLIBC__`


note: initial-exec tls is wrong for both glibc and musl.

(glibc reserves initial tls for ld_audit and dlmopen namespaces, it's
not there for mesa. i.e. this only happens to work because it's
unlikely that a process uses all the glibc features for which static
tls is reserved, but if that happens then mesa will fail to load.)