Re: [RFC][PATCH] clone_with_pids()^w eclone() for x86_64

From: Louis Rilling <Louis.Rilling-aw0BnHfMbSpBDgjK7y7TUQ@public.gmane.org>
To: Dave Hansen <dave-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>
Cc: containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org
Subject: Re: [RFC][PATCH] clone_with_pids()^w eclone() for x86_64
Date: Thu, 19 Nov 2009 22:44:34 +0100	[thread overview]
Message-ID: <20091119214433.GD4767@localdomain> (raw)
In-Reply-To: <1258666356.20093.9622.camel@nimitz>

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On Thu, Nov 19, 2009 at 01:32:36PM -0800, Dave Hansen wrote:
> On Thu, 2009-11-19 at 22:26 +0100, Louis Rilling wrote:
> > But actually this is even better :D:
> > 
> >          __asm__  __volatile__(
> >                   "movq %3, %%r10\n\t"           /* pids in r10*/
> >                   "pushq %%rbp\n\t"              /* save value of ebp */
> >                  :
> >                  :"D" (flags_low), /* rdi */
> >                   "S" (clone_args),/* rsi */
> >                   "d" (args_size), /* rdx */
> >                   "r10" (pids)     /* Linux reads its fourth arg from r10 */
> >                  );
> 
> That gives me:
> 
> clone-lib.c:28: error: matching constraint references invalid operand
> number

?? I know that this syntax works for r8, but I don't remember for r9-r15. I don't
have my handy documentation nearby, so let met check tomorrow (if nobody finds
before).

Anyway, although not optimal, even your first version should be ok with respect
to placing the fourth arg in r10 (assuming that the compiler keeps it until the
next asm statement of course, which any [future?] code instrumentation of the
compiler could break).

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes

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