Re: [Bug c++/37715] New: Different class sizes with public/private and alignments

[Andrew Thomas Pinski <pinskia at gmail dot com>]

Sent from my iPhone

On Oct 2, 2008, at 2:09 AM, "adam at os dot inf dot tu-dresden dot de"  
<gcc-bugzilla@gcc.gnu.org> wrote:

> I've been experiencing some (for me) rather unexpected behavior with  
> some C++
> code. The following is a very reduced test case:

This comes down to non pod vs pod and tail filling.

> class A
> { private: void *one;
> } __attribute__((aligned(16)));
>
> class C {};
> class L { public: class M : A { C _c; }; M m; };
>
> L x;
>
> It's about the size of L::M. I.e. if this file is compiled, L::M has  
> a sizeof
> of 16. If the first private is changed to public, the size of L::M  
> changes to
> 32 (-Dprivate=public). Is this expected behavior? When removing the  
> alignment
> contraints, the size of L::M is 8 in both cases.
>
> I'm seeing this behavior with all gcc versions tested (3.3, 3.4,  
> 4.1, 4.2, 4.3,
> head) as well as with different target architectures (i386, x86_64,  
> arm).
>
> This is the script use to show the difference:
> #! /bin/sh
>
> echo 'print sizeof(L::M)' > x.cmd
>
> echo -n "orig:        "
> gcc -Wall -g -c x.cc
> gdb -x x.cmd -batch x.o
>
> echo -n "with define: "
> gcc -Dprivate=public -Wall -g -c x.cc
> gdb -x x.cmd -batch x.o
>
> Thanks
>
>
> --
>           Summary: Different class sizes with public/private and  
> alignments
>           Product: gcc
>           Version: 4.3.1
>            Status: UNCONFIRMED
>          Severity: normal
>          Priority: P3
>         Component: c++
>        AssignedTo: unassigned at gcc dot gnu dot org
>        ReportedBy: adam at os dot inf dot tu-dresden dot de
> GCC build triplet: i486-linux-gnu
>  GCC host triplet: i486-linux-gnu
> GCC target triplet: i486-linux-gnu
>
>
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=37715