linux-kernel - Re: X32 psABI status update

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Message-Id: <201103210108.49780.vapier@gentoo.org>
Date:	Mon, 21 Mar 2011 01:08:48 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	"H.J. Lu" <hjl.tools@...il.com>
Cc:	libc-alpha@...rceware.org, GCC Development <gcc@....gnu.org>,
	LKML <linux-kernel@...r.kernel.org>, x32-abi@...glegroups.com
Subject: Re: X32 psABI status update

On Thursday, March 17, 2011 01:21:16 H.J. Lu wrote:
> On Wed, Mar 16, 2011 at 7:57 PM, Mike Frysinger <vapier@...too.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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