Re: [libstdc++, testsuite] Add dg-require-thread-fence

[Jonathan Wakely <jwakely at redhat dot com>]

On 20/10/16 10:40 +0100, Jonathan Wakely wrote:
> Please CC the libstdc++ list for libstdc++ patches, this is a
> requirement for patch submission, see https://gcc.gnu.org/lists.html
>
>
> On 20/10/16 09:55 +0200, Christophe Lyon wrote:
> > Hi,
> >
> > Several times I have noticed/reported test failures because some test
> > cases wouldn't link on arm-none-eabi using the default 'old' cpu
> > target: __sync_synchronize cannot be resolved by the linker.
>
> That isn't used by libstdc++ anywhere, so the call to it is being
> emitted by the compiler. It would be good to know where it comes from.
>
>
> > The attached long patch adds
> > +// { dg-require-thread-fence "" }
> > to all the tests that require it according to the error messages I get.
> >
> > The change is mechanical:
> > - insert this line below dg-do if present
> > - insert this line at the top of the file otherwise
> >
> > For instance:
> >
> > diff --git a/libstdc++-v3/testsuite/18_support/bad_typeid/what.cc
> > b/libstdc++-v3/testsuite/18_support/bad_typeid/what.cc
> > index 633175b..a048250 100644
> > --- a/libstdc++-v3/testsuite/18_support/bad_typeid/what.cc
> > +++ b/libstdc++-v3/testsuite/18_support/bad_typeid/what.cc
> > @@ -1,3 +1,4 @@
> > +// { dg-require-thread-fence "" }
> > // 2007-01-30  Paolo Carlini  <pcarlini@suse.de>
> >
> > // Copyright (C) 2007-2016 Free Software Foundation, Inc.
> > diff --git a/libstdc++-v3/testsuite/18_support/cxa_vec.cc
> > b/libstdc++-v3/testsuite/18_support/cxa_vec.cc
> > index e712655..f2a6c5a 100644
> > --- a/libstdc++-v3/testsuite/18_support/cxa_vec.cc
> > +++ b/libstdc++-v3/testsuite/18_support/cxa_vec.cc
> > @@ -1,4 +1,5 @@
> > // { dg-do run }
> > +// { dg-require-thread-fence "" }
> > // Avoid use of non-overridable new/delete operators in shared
> > // { dg-options "-static" { target *-*-mingw* } }
> > // Test __cxa_vec routines
> >
> >
> > If that's OK, I'm not sure how to write the ChangeLog entry: it
> > modifies 3287 files.
> >
> > In my testing, it replaces 3287 FAILs by 3287 UNSUPPORTED.
>
> Wouldn't it be better to remove the dependency on __sync_synchronize
> rather than declare nearly 50% of the testsuite UNSUPPORTED?
>
> If 3287 tests can't use it is the resulting libstdc++.so actually
> useful to anyone?

Are those *all* the tests that link to libstdc++.so / libstdc++.a and
aren't disabled for arm-none-eabi by some other directive? It would be
about the right number.

If Every. Single. Test. that uses the libstdc++ library has this
failure, and the library can't be made to be usable, the answer is
surely to change the meaning of "dg-do run" to not link+run tests, not
add a new directive to Every. Single. Test.  (and every single test we
add in future too!)