Re: X32 psABI status update
From: H.J. Lu
Date: Mon Mar 21 2011 - 02:55:02 EST
On Sun, Mar 20, 2011 at 10:53 PM, Mike Frysinger <vapier@xxxxxxxxxx> wrote:
> On Monday, March 21, 2011 01:35:35 H.J. Lu wrote:
>> On Sun, Mar 20, 2011 at 10:08 PM, Mike Frysinger wrote:
>> > On Thursday, March 17, 2011 01:21:16 H.J. Lu wrote:
>> >> On Wed, Mar 16, 2011 at 7:57 PM, Mike Frysinger 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.
> yes, and my point is that people often reach for cpp defines rather than
> figure out how to do it right.
> i'm not saying that __x32__ should be defined in place of __x86_64__, just
> that when -mx32 is used, __x32__ is additionally defined. simply as an
> example, what i'm referring to could be accomplished by adding this to the
> *cpp specs:
I don't think it will help x32 and I think it will make it harder to
add x32 support.
I still want to see a real usage before I add it.
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