Re: [ARM] EABI and the default to short enums

[Sebastian Huber <sebastian dot huber at embedded-brains dot de>]

On 02/27/2012 10:33 PM, Daniel Jacobowitz wrote:
> Sorry for being late to the party.
>
> On Wed, Feb 15, 2012 at 9:55 AM, Ian Lance Taylor<iant@google.com>  wrote:
> > Ouch, I did not know that the EABI left this open.  That seems like a
> > bug, because it prevents code from being interoperable.  This is
> > precisely the kind of thing an ABI should address.  Does anybody know
> > why they did this?
>
> It's a matter of platform variants.  There are a sufficient number of
> ARM use cases where the extra bytes matter (or else, there are a
> sufficient number of ARM vendors / customers who feel that it
> matters).  But there's also cases like Linux where the advantages of
> int-sized enums outweigh the space cost.  So the platform ABI
> supplement is supposed to decide.
>
> I believe that the Linux variant has other deviations from base than
> just this.  The one I remember in particular is TLS models but there
> may be others.  Please check the full range of differences before you
> decide which would be a better base for RTEMS.

Thanks for the comment.  I just figured out, that in GCC 4.7 
ARM_ABI_AAPCS_LINUX is used for other stuff (e.g. Linux kernel support for 
atomic operations) and not only the enums.  Newlib makes also problems (some 
files of libc are compilied with -fshort-enums).  All in all its probably 
better to fix the XDR library and other things (the assumption that an enum is 
an int is quite common).

--
Sebastian Huber, embedded brains GmbH

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