From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S968284AbcA1Djo (ORCPT ); Wed, 27 Jan 2016 22:39:44 -0500 Received: from ozlabs.org ([103.22.144.67]:56951 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S968260AbcA1Djk (ORCPT ); Wed, 27 Jan 2016 22:39:40 -0500 Message-ID: <1453952378.4108.3.camel@ellerman.id.au> Subject: Re: [PATCH v6 1/9] ppc64 (le): prepare for -mprofile-kernel From: Michael Ellerman To: Alan Modra Cc: Torsten Duwe , Steven Rostedt , Anton Blanchard , Jiri Kosina , linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, live-patching@vger.kernel.org Date: Thu, 28 Jan 2016 14:39:38 +1100 In-Reply-To: <20160127125809.GN17028@bubble.grove.modra.org> References: <20160125170459.14DB7692CE@newverein.lst.de> <20160125170723.D2CCE692CE@newverein.lst.de> <1453889967.10839.2.camel@ellerman.id.au> <20160127125809.GN17028@bubble.grove.modra.org> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5-1ubuntu3.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2016-01-27 at 23:28 +1030, Alan Modra wrote: > On Wed, Jan 27, 2016 at 09:19:27PM +1100, Michael Ellerman wrote: > > Hi Torsten, > > > > On Mon, 2016-01-25 at 16:26 +0100, Torsten Duwe wrote: > > > The gcc switch -mprofile-kernel, available for ppc64 on gcc > 4.8.5, > > > allows to call _mcount very early in the function, which low-level > > > ASM code and code patching functions need to consider. > > > Especially the link register and the parameter registers are still > > > alive and not yet saved into a new stack frame. > > > > > > Signed-off-by: Torsten Duwe > > > --- > > > arch/powerpc/kernel/entry_64.S | 45 +++++++++++++++++++++++++++++++++++++++-- > > > arch/powerpc/kernel/ftrace.c | 12 +++++++++-- > > > arch/powerpc/kernel/module_64.c | 14 +++++++++++++ > > > 3 files changed, 67 insertions(+), 4 deletions(-) > > > > > > diff --git a/arch/powerpc/kernel/entry_64.S b/arch/powerpc/kernel/entry_64.S > > > index a94f155..e7cd043 100644 > > > --- a/arch/powerpc/kernel/entry_64.S > > > +++ b/arch/powerpc/kernel/entry_64.S > > > @@ -1206,7 +1206,12 @@ _GLOBAL(enter_prom) > > > #ifdef CONFIG_DYNAMIC_FTRACE > > > _GLOBAL(mcount) > > > _GLOBAL(_mcount) > > > - blr > > > + std r0,LRSAVE(r1) /* gcc6 does this _after_ this call _only_ */ > > > + mflr r0 > > > + mtctr r0 > > > + ld r0,LRSAVE(r1) > > > + mtlr r0 > > > + bctr > > > > Can we use r11 instead? eg: > > > > _GLOBAL(_mcount) > > mflr r11 > > mtctr r11 > > mtlr r0 > > bctr > > Depends on what you need to support. As Torsten says, the code to > call _mcount when -mprofile-kernel is emitted before the prologue of a > function (similar to -m32), but after the ELFv2 global entry point > code. If you trash r11 here you're killing the static chain pointer, > used by C nested functions or other languages that use a static chain, > eg. Pascal. r11 has *not* been saved for ELFv2. OK, thanks for clarfiying. Pascal is not a big concern :D. But although I don't think we use nested functions anywhere, someone somewhere could be, or at least might one day. > r12 might be a better choice for a temp reg. Even better. cheers