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SubjectRe: X32 psABI status update
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On Thursday, March 17, 2011 01:21:16 H.J. Lu wrote:
> On Wed, Mar 16, 2011 at 7:57 PM, Mike Frysinger <vapier@gentoo.org> wrote:
> > in looking at the gcc files, it doesnt seem like there's any defines
> > setup to declare x32 directly. instead, you'd have to do something
> > like: #ifdef __x86_64__
> > # if __SIZEOF_LONG__ == 8
> > /* x86_64 */
> > # else
> > /* x32 */
> > # endif
> > #endif
> >
> > any plans on adding an __x32__ (or whatever) cpp symbol to keep people
> > from coming up with their own special/broken crap ? or are there some
> > already that i'm not seeing ?
>
> The idea is in most cases, you only need to check __x86_64__ since x32 and
> x86-64 are very close. In some cases, x32 is very different from x86_64,
> like assembly codes on long and pointer, you can check __x86_64__ and
> __LP64__. In glibc, I used a different approach by using macros REG_RAX,
> .., MOV_LP, ADD_LP, SUB_LP and CMP_LP in assembly codes.

while i agree with you in general that this is how people should be doing
things, in practice i often see people fishing around. education only goes so
far, so if there was an __x32__ define, i feel like people are more likely to
get it right than wrong.

i dont have any use cases off the top of my head, but i wouldnt be surprised
if the heavy inline assembly people (like the multimedia peeps e.g. libav)
approached it this way. rather than google for documentation, look at the cpp
output between -m64 and -mx32 and see what sticks out. "__x32__" would
certainly do that.
-mike
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