[Mesa-dev] [LLVMdev] mesa-10.4.4: BROKEN TLS support in GLXwith llvm-toolchain v3.6.0rc2

[Marc Dietrich]

Am Samstag, 14. Februar 2015, 18:20:12 schrieb Dimitry Andric:
> On 11 Feb 2015, at 11:16, Sedat Dilek <sedat.dilek at gmail.com> wrote:
> > On Wed, Feb 11, 2015 at 12:09 AM, Emil Velikov <emil.l.velikov at gmail.com> 
wrote:
> >> On 10/02/15 13:17, Dimitry Andric wrote:
> >>> On 09 Feb 2015, at 18:52, Sedat Dilek <sedat.dilek at gmail.com> wrote:
> >>>> On Mon, Feb 9, 2015 at 6:44 PM, Emil Velikov <emil.l.velikov at gmail.com> 
wrote:
> >>>>> On 07/02/15 22:42, Sedat Dilek wrote:
> >>> ...
> >>> 
> >>>>>> In file included from ../../src/mapi/entry.c:49:
> >>>>>> ./entry_x86-64_tls.h:66:1: warning: tentative array definition
> >>>>>> assumed
> >>>>>> to have one element
> >>>>>> x86_64_entry_start[];
> >>>>>> ^
> >>>>>> fatal error: error in backend: symbol 'x86_64_entry_start' is already
> >>>>>> defined>>> 
> >>> ...
> >>> 
> >>>>> It may be that it's a bug on our end, but it's a bit painful going
> >>>>> through all the auto generated sources, the 10+ define guards and
> >>>>> other
> >>>>> magic that's inside src/mapi. Getting some idea on llvm/clang
> >>>>> behaviour
> >>>>> change should help out :-)
> >>>>> 
> >>>>> Please open a bug-report with llvm and/or mesa, so that we have all
> >>>>> the
> >>>>> info in one place and things don't get lost.
> >>>> 
> >>>> I am unsure if it is a bug in llvm/clang or in mesa.
> >>>> Shall I open 2 bug-reports - in mesa and llvm BTS?
> >>> 
> >>> Please have a look at this PR, which I opened in May 2014, and which is 
about the same issue:
> >>>  http://llvm.org/PR19778
> >> 
> >> Hi Dimitry,
> >> 
> >> From a quick look at the bug, the llvm/clang devs are quoting the C11
> >> spec, yet we're not building with -std=c11 so I'm not sure that applies.
> >> Feel free to forward that if interested - I'm a bit short on account on
> >> their bugzilla :-)
> >> 
> >>> The assertion seems to have been transformed now into a backend error,
> >>> but this may also be because you built clang without assertions. (Did
> >>> you?)>>> 
> >>> In any case, the workaround is to change the static symbols into extern 
symbols, together with a hidden visibility attribute (as suggested by Rafael 
Espíndola), similar to the fix I posted in this FreeBSD port bug:
> >>>  https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=192286
> >>> 
> >>> E.g., you can use these patches:
> >>> 
> >>> https://svnweb.freebsd.org/ports/head/graphics/libGL/files/patch-src__ma
> >>> pi__entry_x86-64_tls.h?view=markup
> >>> https://svnweb.freebsd.org/ports/head/graphics/libGL/files/patch-src__m
> >>> api__entry_x86_tls.h?view=markup
> >>> https://svnweb.freebsd.org/ports/head/graphics/libGL/files/patch-src__m
> >>> api__entry_x86_tsd.h?view=markup>> 
> >> These patches don't look at all bad. Can you give them a bit of TLS and
> >> send them to the list, please ? This also stands for the other patches
> >> in FreeBSD's repo :-)
> > 
> > On the one hand I am glad to see that there are patches available.
> > I will give them a try when I am at home.
> > On the other hand - knowing FreeBSD switched to llvm/clang as
> > default-compiler - it's abit pity to see that stuff like this is not
> > shared with upstream (did not look at the date of submission).
> > If you have more patches in this area, please share them with upstream.
> 
> The complete collection is here:
> 
> https://svnweb.freebsd.org/ports/head/graphics/libGL/files/
> 
> I didn't create most of these patches, so I can't really say what the
> reason for them was, or whether they still apply to Mesa master.
> 
> In any case, for this specific issue with Mesa's TLS related definitions
> breaking clang, please consider the attached patch.

I think there is no need to restrict this to clang only as it also works with 
gcc. I submitted a slightly different version to the mesa list which uses a 
macro instead and also adds some credits.

Marc
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