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

[Christophe Lyon <christophe dot lyon at linaro dot org>]

On 20 October 2016 at 18:51, Jonathan Wakely <jwakely@redhat.com> wrote:
> 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!)
>
I'm not sure what you really mean here.
I can see 147 execution tests pass, 1 fail.
and 3287 fail to link.

So that's most of the executable tests, yes.

And I agree that my patch is not a viable solution.