linux-kernel - RE: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6 arguments

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Date:   Tue, 22 Mar 2022 15:11:23 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Alviro Iskandar Setiawan' <alviro.iskandar@...weeb.org>
CC:     Willy Tarreau <w@....eu>, Ammar Faizi <ammarfaizi2@...weeb.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Nugraha <richiisei@...il.com>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        GNU/Weeb Mailing List <gwml@...r.gnuweeb.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>
Subject: RE: [RFC PATCH v2 3/8] tools/nolibc: i386: Implement syscall with 6
 arguments

From: Alviro Iskandar Setiawan
> Sent: 22 March 2022 14:48
> 
> On Tue, Mar 22, 2022 at 8:37 PM David Laight wrote:
> > dunno, 'asm' register variables are rather more horrid and
> > should probably only be used (for asm statements) when there aren't
> > suitable register constraints.
> >
> > (I'm sure there is a comment about that in the gcc docs.)
> 
> I don't find the comment that says so here:
> https://gcc.gnu.org/onlinedocs/gcc/Local-Register-Variables.html

I've probably inferred it from:
    "The only supported use for this feature is to specify registers for
    input and output operands when calling Extended asm (see Extended Asm).
    This may be necessary if the constraints for a particular machine don’t
    provide sufficient control to select the desired register."

Here is isn't necessary because the required constraint exist/

	David

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