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Violators will be prosecuted; (version=TLSv1/SSLv3 cipher=AES256-GCM-SHA384 bits=256/256) Fri, 17 May 2019 18:38:09 +0100 Received: from d06av25.portsmouth.uk.ibm.com (d06av25.portsmouth.uk.ibm.com [9.149.105.61]) by b06cxnps4076.portsmouth.uk.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id x4HHc8iJ53280800 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 17 May 2019 17:38:08 GMT Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 9C33611C04C; Fri, 17 May 2019 17:38:08 +0000 (GMT) Received: from d06av25.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 0691D11C050; Fri, 17 May 2019 17:38:08 +0000 (GMT) Received: from localhost (unknown [9.85.68.14]) by d06av25.portsmouth.uk.ibm.com (Postfix) with ESMTP; Fri, 17 May 2019 17:38:07 +0000 (GMT) Date: Fri, 17 May 2019 22:55:43 +0530 From: "Naveen N. Rao" Subject: Re: [RFC PATCH] powerpc/64/ftrace: mprofile-kernel patch out mflr To: linuxppc-dev@lists.ozlabs.org, Michael Ellerman , Nicholas Piggin References: <20190413015940.31170-1-npiggin@gmail.com> <871s13ujcf.fsf@concordia.ellerman.id.au> <1557729790.fw18xf9mdt.naveen@linux.ibm.com> <87tvdytwo0.fsf@concordia.ellerman.id.au> <1557821918.xbleq18bk2.naveen@linux.ibm.com> <1557985279.4o349j5g2i.astroid@bobo.none> <1557989161.cjlaryiij4.naveen@linux.ibm.com> <1558084179.fz93ts375u.astroid@bobo.none> In-Reply-To: <1558084179.fz93ts375u.astroid@bobo.none> User-Agent: astroid/0.14.0 (https://github.com/astroidmail/astroid) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable X-TM-AS-GCONF: 00 x-cbid: 19051717-0016-0000-0000-0000027CD5E1 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 19051717-0017-0000-0000-000032D9B3E3 Message-Id: <1558113815.l84ajqay2l.naveen@linux.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:, , definitions=2019-05-17_10:, , signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=666 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905170105 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Nicholas Piggin wrote: > Naveen N. Rao's on May 17, 2019 4:22 am: >=20 >> While enabling ftrace, we will first need to patch the preceding 'mflr=20 >> r0' (which would now be a 'nop') with 'b +8', then use=20 >> synchronize_rcu_tasks() and finally patch in 'bl _mcount()' followed by=20 >> 'mflr r0'. >>=20 >> I think that's what you meant, just that my reference to patching 'mflr=20 >> r0' with a 'b +8' should have called out that the mflr would have been=20 >> nop'ed out. >=20 > I meant that we don't need the b +8 anywhere, because the mflr r0 > is harmless. Enabling ftrace just needs to patch in 'mflr r0', and > then synchronize_rcu_tasks(), and then patch in 'bl _mcount'. I think? Ah, that's a good point! That should be enough and it simplifies this=20 further. Thanks, Naveen =