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


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 ...

Bye,
Ulrich

-- 
  Dr. Ulrich Weigand
  GNU/Linux compilers and toolchain
  Ulrich.Weigand@de.ibm.com


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