linux-kernel - Re: X32 psABI status update

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Date:	Sun, 20 Mar 2011 22:35:35 -0700
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	Mike Frysinger <vapier@...too.org>
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 Sun, Mar 20, 2011 at 10:08 PM, Mike Frysinger <vapier@...too.org> wrote:
> 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.

My point is __x86_64__ version should work for both 64bit and x32. There should
no need for a separate x32 version.


-- 
H.J.
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