Re: [PATCH] Use ATTRIBUTE_PACKED in ree.c

[Richard Earnshaw <rearnsha at arm dot com>]

On 22/11/12 07:52, Jakub Jelinek wrote:
> On Thu, Nov 22, 2012 at 12:26:01AM +0100, Eric Botcazou wrote:
> > > 2012-11-21  Jakub Jelinek  <jakub@redhat.com>
> > >
> > > 	* ree.c (struct ext_modified): Add ATTRIBUTE_PACKED.
> >
> > Are you sure that this will compile with non-GCC compilers?
>
> I'm not sure, but I hope it will.  ansidecl.h has
> #ifndef GCC_VERSION
> #define GCC_VERSION (__GNUC__ * 1000 + __GNUC_MINOR__)
> #endif /* GCC_VERSION */
> ...
> #if (GCC_VERSION < 2007)
> # define __attribute__(x)
> #endif
> ...
> #ifndef ATTRIBUTE_PACKED
> # define ATTRIBUTE_PACKED __attribute__ ((packed))
> #endif
>
> So in theory it should expand to nothing for non-GCC compilers.
> I've tested (on a short testcase matching what the decl does)
> GCCs from 4.8 down back to 3.2 (we support 4.1+ only anyway now)
> and clang 3.0.
>
> 	Jakub

That's not going to help if those other compilers need packedness to 
eliminate padding.  The /old/ ARM ABI used to require that all structs 
were padded out to 32 bits.

It looks to me as though this code is just non-portable and as such 
needs to be rewritten :-(

R.