linux-kernel - Re: X32 psABI status

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Message-ID: <AANLkTinkCEoX1b71-G94NMpARyvaJ37etE93iTm3EMf7@mail.gmail.com>
Date:	Sun, 13 Feb 2011 15:50:40 -0800
From:	"H.J. Lu" <hjl.tools@...il.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Arnd Bergmann <arnd@...db.de>,
	x32-abi@...glegroups.com, GCC Development <gcc@....gnu.org>,
	GNU C Library <libc-alpha@...rceware.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: X32 psABI status

On Sun, Feb 13, 2011 at 3:39 PM, Alan Cox <alan@...rguk.ukuu.org.uk> wrote:
>> a. the int $0x80 instruction is much slower than syscall.  An actual
>>    i386 process can use the syscall instruction which is disambiguated
>>    by the CPU based on mode, but an x32 process is in the same CPU mode
>>    as a normal 64-bit process.
>
> So set a flag, whoopee
>
>> b. 64-bit arguments have to be split between two registers for the
>>    i386 entry points, requiring user-space stubs.
>
> Diddums. Given you've yet to explain why everyone desperately needs this
> extra interface why do we care ?
>
>> All in all, the cost of an extra system call table is quite modest.
>
> And the cost of not doing it is a gloriously wonderful zero. Yo've still
> not explained the justification or what large number of apps are going to
> use it.
>
> It's a simple question - why do we care, why do we want the overhead and
> the hassle, what do users get in return ?
>

The real question is if we need to use ia32.  If the answer is yes, then
x32 provides the benefit of ia32 with register extended to 64bit plus 8
more registers as well as IP relative address.

-- 
H.J.
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