[PATCH] libstdc++-v3: Have aligned_alloc() on Newlib

[Sebastian Huber]

On 08/08/18 16:01, Jonathan Wakely wrote:
> On 08/08/18 15:57 +0200, Ulrich Weigand wrote:
>> Jonathan Wakely wrote:
>>> On 08/08/18 10:52 +0200, Sebastian Huber wrote:
>>> >While building for Newlib, some configure checks must be hard coded.
>>> >The aligned_alloc() is supported since 2015 in Newlib.
>>> >
>>> >libstdc++-v3
>>> >
>>> >    PR target/85904
>>> >    * configure.ac): Define HAVE_ALIGNED_ALLOC if building for
>>>
>>> There's a stray closing parenthesis here.
>>>
>>> >    Newlib.
>>> >    * configure: Regnerate.
>>>
>>> Typo "Regnerate".
>>>
>>> But the patch itself is fine - OK for trunk.
>>>
>>> I'm ambivalent about this being backported to gcc-7 and gcc-8 branches
>>> (gcc-6 is unaffected as it doesn't use aligned_alloc).
>>>
>>> It's strictly speaking an ABI change, because HAVE_ALIGNED_ALLOC
>>> affects the memory layout for allocations from operator new(size_t,
>>> align_val_t) (in new_opa.cc) which needs to agree with the
>>> corresponding operator delete (in del_opa.cc). Using static linking it
>>> might be possible to create a binary that has operator new using
>>> aligned_alloc, but operator delete expecting to do ((void**)ptr)[-1],
>>> which would be bad.
>>>
>>> Those operators are C++17, so "experimental", but maybe we shouldn't
>>> make the change on release branches.
>>
>> The way it is now I'm getting build failures on new SPU target
>> (which is newlib based):
>>
>> /home/uweigand/dailybuild/spu-tc-2018-08-07/gcc-head/src/libstdc++-v3/libsupc++/new_opa.cc:58:1: 
>> error: 'void* aligned_alloc(std::size_t, std::size_t)' was declared 
>> 'extern' and later 'static' [-fpermissive]
>> aligned_alloc (std::size_t al, std::size_t sz)
>> ^~~~~~~~~~~~~
>> In file included from 
>> /home/uweigand/dailybuild/spu-tc-2018-08-07/gcc-build/spu/libstdc++-v3/include/cstdlib:75:62,
>>                 from 
>> /home/uweigand/dailybuild/spu-tc-2018-08-07/gcc-build/spu/libstdc++-v3/include/stdlib.h:36,
>>                 from 
>> /home/uweigand/dailybuild/spu-tc-2018-08-07/gcc-head/src/libstdc++-v3/libsupc++/new_opa.cc:27:
>> /home/uweigand/dailybuild/spu-tc-2018-08-07/spu-toolchain/spu/include/stdlib.h:328:8: 
>> note: previous declaration of 'void* aligned_alloc(size_t, size_t)'
>> void * aligned_alloc(size_t, size_t) __malloc_like __alloc_align(1)
>>        ^~~~~~~~~~~~~
>>
>> This seems to be because configure is hard-coded to assume aligned_alloc
>> is not available, but then the new_opc.cc file tries to define its own
>> version, conflicting with the newlib prototype that is actually there.
>>
>> So one way or the other this needs to be fixed ...
>
> But that's on trunk, right? Sebastian is about to fix that.
>
> I expect the same problem exists on the branches too though.
>
> I'm surprised nobody has reported this until now. It's been like that
> since r244933 in Jan 2017. 

I notices this problem today with a build of the GCC 7 branch. I am able 
to build a GCC 7.3.0.

-- 
Sebastian Huber, embedded brains GmbH

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