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Wed, 24 Aug 2022 07:30:55 GMT Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 833FCA404D; Wed, 24 Aug 2022 07:30:55 +0000 (GMT) Received: from d06av23.portsmouth.uk.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7DF2DA4053; Wed, 24 Aug 2022 07:30:53 +0000 (GMT) Received: from [9.197.255.133] (unknown [9.197.255.133]) by d06av23.portsmouth.uk.ibm.com (Postfix) with ESMTP; Wed, 24 Aug 2022 07:30:53 +0000 (GMT) Message-ID: <774d9664-b36b-67c6-7cb5-7795aac0ce87@linux.ibm.com> Date: Wed, 24 Aug 2022 15:30:51 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:91.0) Gecko/20100101 Thunderbird/91.6.1 Subject: Re: [PATCH v3] rs6000: Rework ELFv2 support for -fpatchable-function-entry* [PR99888] Content-Language: en-US To: Segher Boessenkool Cc: GCC Patches , David Edelsohn , AlanM References: <20220818173435.GN25951@gate.crashing.org> <20220823143310.GV25951@gate.crashing.org> From: "Kewen.Lin" In-Reply-To: <20220823143310.GV25951@gate.crashing.org> Content-Type: text/plain; charset=UTF-8 X-TM-AS-GCONF: 00 X-Proofpoint-GUID: 1RvxQn7bAEeHji4k4VBx6Nf5iiZAO-41 X-Proofpoint-ORIG-GUID: UdwPApS6BZ2U9v63pF-eblPdXHwL5AuT Content-Transfer-Encoding: 7bit X-Proofpoint-UnRewURL: 0 URL was un-rewritten MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.205,Aquarius:18.0.895,Hydra:6.0.517,FMLib:17.11.122.1 definitions=2022-08-24_04,2022-08-22_02,2022-06-22_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 spamscore=0 impostorscore=0 suspectscore=0 mlxlogscore=999 malwarescore=0 mlxscore=0 bulkscore=0 priorityscore=1501 lowpriorityscore=0 clxscore=1015 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2207270000 definitions=main-2208240028 X-Spam-Status: No, score=-4.3 required=5.0 tests=BAYES_00,DKIM_SIGNED,DKIM_VALID,DKIM_VALID_EF,KAM_SHORT,NICE_REPLY_A,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_PASS,TXREP,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on server2.sourceware.org List-Id: Hi Segher, on 2022/8/23 22:33, Segher Boessenkool wrote: > On Fri, Aug 19, 2022 at 10:40:10AM +0800, Kewen.Lin wrote: >> Since you proposed to update the documentation, I'm thinking if we can >> reconsider Fangrui's proposal in the PR which Alan seconded: Put preceding >> nops before GEP and succeeding nops after LEP. Previously I had the concern >> that the nops inserted doesn't respect to a same function entry, it looks >> inconsistent to the documentation, and you also noted that "The nops have >> to be consecutive". If we want to update the documentation, could we reword >> it for PowerPC ELFv2 ABI? >> >> What's your opinion? > > I'm not sure what the question is, sorry. > Sorry for confusion. The question is that if we can consider the proposal in [1], by noting the particularity on ppc64le in documentation. btw, I did some searching on why the feature supports preceding nops, and commented it in [2]. > If you want different semantics for ELFv2 (which might well be useful), > we need some new command line option for that. > Not sure if we really needs one new command line option, dual entries on ppc64le is special comparing with a normal unique function entry, couldn't it be a special case in the documentation? > I suggested here to just describe in the existing doc what is done for > global and local entry points on ELFv2. > Yeah, you have suggested nice wordings "For PowerPC with the ELFv2 ABI, there will be M nops before the local entry point, and N-M after". I thought if we can consider [1] and updated the documentation similarly like "For PowerPC with the ELFv2 ABI, there will be M nops before the global entry point, and N-M after the local entry point". [1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99888#c5 [2] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=99888#c10 BR, Kewen