Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761689AbZCQA7q (ORCPT ); Mon, 16 Mar 2009 20:59:46 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751715AbZCQA7g (ORCPT ); Mon, 16 Mar 2009 20:59:36 -0400 Received: from smtp-outbound-2.vmware.com ([65.115.85.73]:44998 "EHLO smtp-outbound-2.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751339AbZCQA7g (ORCPT ); Mon, 16 Mar 2009 20:59:36 -0400 Subject: Re: [PATCH] x86-paravirt: prevent gcc from generating the wrong addressing mode From: Alok Kataria Reply-To: akataria@vmware.com To: Jeremy Fitzhardinge Cc: "H. Peter Anvin" , the arch/x86 maintainers , Linux Kernel Mailing List In-Reply-To: <49BEEDC2.2070809@goop.org> References: <49BEEDC2.2070809@goop.org> Content-Type: text/plain Organization: VMware INC. Date: Mon, 16 Mar 2009 17:59:34 -0700 Message-Id: <1237251574.5906.24.camel@alok-dev1> Mime-Version: 1.0 X-Mailer: Evolution 2.8.0 (2.8.0-40.el5_1.1) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1962 Lines: 52 Thanks Jeremy. Acked-by: Alok N Kataria On Mon, 2009-03-16 at 17:24 -0700, Jeremy Fitzhardinge wrote: > When we generate a call sequence for calling a paravirtualized > function, we presume that the generated code is "call *0xXXXXX", > which is a 6 byte opcode; this is larger than a normal > direct call, and so we can patch a direct call over it. > > At the moment, however we give gcc enough rope to hang us by > putting the address in a register and generating a two byte > indirect-via-register call. Prevent this by explicitly > dereferencing the function pointer and passing it into the > asm as a constant. > > This prevents crashes in VMI, as it cannot handle unpatchable > callsites. > > Signed-off-by: Jeremy Fitzhardinge > Cc: Alok Kataria > > diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h > index d4fec1f..6922d16 100644 > --- a/arch/x86/include/asm/paravirt.h > +++ b/arch/x86/include/asm/paravirt.h > @@ -395,7 +395,7 @@ extern struct pv_lock_ops pv_lock_ops; > > #define paravirt_type(op) \ > [paravirt_typenum] "i" (PARAVIRT_PATCH(op)), \ > - [paravirt_opptr] "m" (op) > + [paravirt_opptr] "i" (&(op)) > #define paravirt_clobber(clobber) \ > [paravirt_clobber] "i" (clobber) > > @@ -449,7 +449,7 @@ int paravirt_disable_iospace(void); > * offset into the paravirt_patch_template structure, and can therefore be > * freely converted back into a structure offset. > */ > -#define PARAVIRT_CALL "call *%[paravirt_opptr];" > +#define PARAVIRT_CALL "call *%c[paravirt_opptr];" > > /* > * These macros are intended to wrap calls through one of the paravirt > > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/