From mboxrd@z Thu Jan  1 00:00:00 1970
From: Guillaume Rousse <Guillaume.Rousse@inria.fr>
Subject: Re: porting xen-detect ASM code into a shared library
Date: Thu, 10 Jul 2008 13:42:18 +0200
Message-ID: <4875F59A.3060107@inria.fr>
References: <C49BA9C5.23DBD%keir.fraser@eu.citrix.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: quoted-printable
Return-path: <xen-devel-bounces@lists.xensource.com>
In-Reply-To: <C49BA9C5.23DBD%keir.fraser@eu.citrix.com>
List-Unsubscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xensource.com>
List-Help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-Subscribe: <http://lists.xensource.com/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
Sender: xen-devel-bounces@lists.xensource.com
Errors-To: xen-devel-bounces@lists.xensource.com
To: Keir Fraser <keir.fraser@eu.citrix.com>
Cc: xen-devel@lists.xensource.com
List-Id: xen-devel@lists.xenproject.org

Keir Fraser a =E9crit :
> On 10/7/08 11:54, "Guillaume Rousse" <Guillaume.Rousse@inria.fr> wrote:
>=20
>> I turned it into the current way because I don't need the check in pv
>> context, but I guess it might be simplified.
>=20
> Actually then you can take the xc_cpuid_x86 function pretty much unmodi=
fied
> (of course regs[0-3] become eax-edx, and input[1] is not needed).
>=20
> The other stuff in the asm code is to ensure that cpuid traps into the
> hypervisor when run in a pv guest. If you don't need to run in a pv gue=
st
> then you don't need that extra code.
OK, I tried this:

void Xen_cpuid(uint32_t idx, uint32_t *eax, uint32_t *ebx, uint32_t=20
*ecx, uint32_t *edx)

{
      asm (
         /* %ebx register need to be saved before usage and restored=20
thereafter
          * for PIC-compliant code on i386 */
#ifdef __i386__
         "push %%ebx; cpuid; mov %%ebx,%1; pop %%ebx"
#else
         "push %%rbx; cpuid; mov %%ebx,%1; pop %%rbx"
#endif
         : "=3Da" (*eax), "=3Dr" (*ebx), "=3Dc" (*ecx), "=3Dd" (*edx)
         : "" (idx), "2" (0) );

But it doesn't build:
misc.c: In function 'Xen_cpuid':
misc.c:1377: warning: asm operand 4 probably doesn't match constraints
misc.c:1377: error: impossible constraint in 'asm'

According to what I understood from GCC-Inline-Assembly-HOWTO, the 4th=20
operand is probably "=3Dd" (*edx), but I don't see the exact issue.
--=20
Guillaume Rousse
Moyens Informatiques - INRIA Futurs
Tel: 01 69 35 69 62