Re: [Qemu-devel] [PATCH] tests: vm: auto_install OpenBSD

[Brad Smith]

On 8/24/2018 10:46 AM, Peter Maydell wrote:

> On 24 August 2018 at 15:43, Daniel P. Berrangé <address@hidden> wrote:
> > On Fri, Aug 24, 2018 at 10:36:30AM -0400, Brad Smith wrote:
> > > I very much appreciate the effort to bump up to 6.3 as I was going
> > > to suggest doing that at some point. But bumping up to 6.3 at the
> > > moment will fail with the configure script. We've switched from GCC 4.2
> > > to Clang. The TLS check will fail with Clang's emulated TLS. We've
> > > had a local patch for awhile to fix the test but I don't think it is
> > > appropriate to upstream as is.
> > >
> > > Index: configure
> > > --- configure.orig
> > > +++ configure
> > > @@ -1876,7 +1876,7 @@ static __thread int tls_var;
> > >   int main(void) { return tls_var; }
> > >   EOF
> > > -if ! compile_prog "-Werror" "" ; then
> > > +if ! compile_prog "-Werror" "-pthread" ; then
> > >       error_exit "Your compiler does not support the __thread specifier for " \
> > >        "Thread-Local Storage (TLS). Please upgrade to a version that does."
> > >   fi
> > Later on in the configure script there's a check for pthreads that
> > sets $PTHREAD_LIB to the desired arg.
> >
> > Best is probably to move that check higher up, and then use $PTHREAD_LIB
> > as the argument to the compile_prog call you show.
> Is emulated TLS a sufficiently complete/performant TLS
> implementation for our purposes?

I won't make any claims for performance but it's been used for 2 1/2 
years now
with QEMU with GCC 4.9 and recently with Clang. The various 
libraries/apps and
so forth that we had issues in the past with TLS all seem to work Ok. 
It's used on
Android too. Both newer versions of GCC and Clang implement this.

> (I think it would be better if OpenBSD just implemented real TLS
> like every other host OS we support.)
There is very much a desire to do so and it will be completed at some 
point. I
know some work has gone into our threads library and linker towards 
implementing
TLS but it's hasn't been completed yet. I have no idea how long it will 
be or what
is currently holding things up but I know it won't be anytime soon.