Segmentation fault when using Vc::Memory as a member of a heap-allocated object

[Sandro Wenzel]

I think I can resolve this issue:

In fact with "A a()" the Vc memory is correctly aligned in the stack while
"A * a = new A()" does not align the object per default.
@Georgios: I have written a custom new operator which achieves this. It is
in the repository.

Best

Sandro


[please enable javascript to see the address]>:

> Hi everyone,
>
> I would like to report an issue I came across while using Vc. Here is a
> short example that reproduces it:
>
> #include <Vc/Vc>
>
> class A {
>     private:
>         Vc::Memory<Vc::double_v, 3> internal;
> };
>
> int main() {
>     std::cout << "size: " << Vc::double_v::Size << std::endl;
>     A *a = new A();
>     return 0;
> }
>
>
> The example compiles but segfaults during the creation of object a.
>
> $ ./a.out
> size: 4
> Segmentation fault
>
>
> Backtrace:
>
> $ gdb ./a.out
> GNU gdb (GDB) 7.5.91.20130417-cvs-ubuntu
> Copyright (C) 2013 Free Software Foundation, Inc.
> License GPLv3+: GNU GPL version 3 or later <
> http://gnu.org/licenses/gpl.html>
> This is free software: you are free to change and redistribute it.
> There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
> and "show warranty" for details.
> This GDB was configured as "x86_64-linux-gnu".
> For bug reporting instructions, please see:
> <http://www.gnu.org/software/gdb/bugs/>...
> Reading symbols from /tmp/vcmemory/a.out...done.
> (gdb) r
> Starting program: /tmp/vcmemory/a.out
> size: 4
> Program received signal SIGSEGV, Segmentation fault.
> 0x000000000040142f in _mm256_store_pd (__A=..., __P=0x604010) at
> /usr/lib/gcc/x86_64-linux-gnu/4.7/include/avxintrin.h:829
> 829  *(__m256d *)__P = __A;
> (gdb) bt
> #0  0x000000000040142f in _mm256_store_pd (__A=..., __P=0x604010) at
> /usr/lib/gcc/x86_64-linux-gnu/4.7/include/avxintrin.h:829
> #1  store<Vc::v0::Public::{anonymous}::LoadStoreFlags<> > (x=...,
> mem=0x604010) at
> /opt/Vc-a1d8b9fc31060d870386613cc72319546c850b87/include/Vc/avx/vectorhelper.h:106
> #2  store<double, Vc::v0::Public::{anonymous}::LoadStoreFlags<> >
> (flags=..., mem=0x604010, this=0x7fffffffe420) at
> /opt/Vc-a1d8b9fc31060d870386613cc72319546c850b87/include/Vc/avx/vector.tcc:236
> #3  store<Vc::v0::Public::{anonymous}::LoadStoreFlags<> > (flags=...,
> mem=0x604010, this=<optimized out>) at
> /opt/Vc-a1d8b9fc31060d870386613cc72319546c850b87/include/Vc/avx/vector.h:174
> #4  operator=<Vc::v0::AVX::Vector<double> > (x=..., this=0x604010) at
> /opt/Vc-a1d8b9fc31060d870386613cc72319546c850b87/include/Vc/common/memorybase.h:85
> #5  Vc::v0::Common::Memory<Vc::v0::AVX::Vector<double>, 3ul, 0ul,
> true>::Memory (this=0x604010) at
> /opt/Vc-a1d8b9fc31060d870386613cc72319546c850b87/include/Vc/common/memory.h:293
> #6  0x00000000004011aa in A::A (this=0x604010) at main.cpp:4
> #7  0x00000000004010fa in main () at main.cpp:11
>
>
> The above code was compiled with:
>
> g++ -fabi-version=6 -m64 -std=c++11  -g -fpermissive -ffast-math
>  -finline-limit=10000000 -mavx -ftree-vectorize main.cpp
> -I/opt/Vc-a1d8b9fc31060d870386613cc72319546c850b87/include
> -L/opt/Vc-a1d8b9fc31060d870386613cc72319546c850b87/lib/ -lVc -std=c++11
>
>
> I took the latest commit of Vc (a1d8b9fc31060d870386613cc72319546c850b87),
> compiled and run on a Xeon E3-1280 v3 (Haswell) @ 3.60 GHz by g++
> version 4.7.3-2ubuntu4.
>
> On the contrary, if I replace "A *a = new A()" with "A a()" it runs fine.
> This appears to happen only when the object is allocated on the heap, not
> on the stack.
>
> Is this a bug on the part of Vc or am I doing something wrong?
>
> Cheers
>
> _______________________________________________
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>
>
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