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Mon, 8 Dec 2025 15:38:18 GMT Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id E75D520040; Mon, 8 Dec 2025 15:38:17 +0000 (GMT) Received: from smtpav04.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 7CC0C2004E; Mon, 8 Dec 2025 15:38:16 +0000 (GMT) Received: from [9.111.221.3] (unknown [9.111.221.3]) by smtpav04.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 8 Dec 2025 15:38:16 +0000 (GMT) Message-ID: <11b2438c-ef1f-423f-96c9-3005a75ec008@linux.ibm.com> Date: Mon, 8 Dec 2025 16:38:16 +0100 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [RFC PATCH v2 14/15] unwind_user/backchain: Introduce back chain user space unwinding To: Josh Poimboeuf Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-s390@vger.kernel.org, bpf@vger.kernel.org, x86@kernel.org, Steven Rostedt , Heiko Carstens , Vasily Gorbik , Ilya Leoshkevich , Masami Hiramatsu , Mathieu Desnoyers , Peter Zijlstra , Ingo Molnar , Jiri Olsa , Arnaldo Carvalho de Melo , Namhyung Kim , Thomas Gleixner , Andrii Nakryiko , Indu Bhagat , "Jose E. Marchesi" , Beau Belgrave , Linus Torvalds , Andrew Morton , Florian Weimer , Kees Cook , "Carlos O'Donell" , Sam James , Dylan Hatch References: <20251205171446.2814872-1-jremus@linux.ibm.com> <20251205171446.2814872-15-jremus@linux.ibm.com> Content-Language: en-US From: Jens Remus Organization: IBM Deutschland Research & Development GmbH In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMjA2MDAyMCBTYWx0ZWRfX1grYLRgFzTZ3 6Bw2Y4KLfWHcTiIY8Y+q/40vMo5DISBPf6WqrACaJC3lTWr3YuNditWdGBvOE50K7FO18iHLYkL N+q1ZC8XPnvBwcoqJfdSAfOGem02OMhjdPnKO9MI5Q4zgIbhTpkemspxKuBdCj4Rn+eiIOB8Yug jzP2KFajjhB9mPqExO/heQEaiD1fkTNaF8pi8h7StawqzRXDb1VLiLurUW5jffw4zQ7RphSGH1I RKL6ciLTTZexBxhJFh2Vzgqal3IQxN6ZvqlZg9zUV7SQs/00pUWBtai9/7H44N4lhMqA9k3B8S8 bJmFNkhIDZLiqxjQtuzK0ZoGuhwf72Ycxn8DUippxtkLbYsSlQaT2WQfb6j1OwwfDq9Fqo4uFQ9 H0mnb1/3gsQqmX0zZDtlGk2SX3uRDA== X-Proofpoint-GUID: DXuAST9Co_tE0Nz77KIRNVh0G2HS3M53 X-Proofpoint-ORIG-GUID: J4Duk8KbAVtSEM7aBteiKz0qR3AIXoxE X-Authority-Analysis: v=2.4 cv=O/U0fR9W c=1 sm=1 tr=0 ts=6936f0f0 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=wP3pNCr1ah4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=VnNF1IyMAAAA:8 a=0MvmVg10__VCTnNSAJcA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.9,FMLib:17.12.100.49 definitions=2025-12-06_02,2025-12-04_04,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 lowpriorityscore=0 bulkscore=0 clxscore=1015 phishscore=0 suspectscore=0 adultscore=0 spamscore=0 malwarescore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.19.0-2510240000 definitions=main-2512060020 Hello Josh, thank you for your feedback! On 12/7/2025 4:10 PM, Josh Poimboeuf wrote: > On Fri, Dec 05, 2025 at 06:14:45PM +0100, Jens Remus wrote: >> @@ -159,6 +165,10 @@ static int unwind_user_next(struct unwind_user_state *state) >> if (!unwind_user_next_fp(state)) >> return 0; >> continue; >> + case UNWIND_USER_TYPE_BACKCHAIN: >> + if (!unwind_user_next_backchain(state)) >> + return 0; >> + continue; /* Try next method. */ >> default: >> WARN_ONCE(1, "Undefined unwind bit %d", bit); >> break; >> @@ -187,6 +197,8 @@ static int unwind_user_start(struct unwind_user_state *state) >> state->available_types |= UNWIND_USER_TYPE_SFRAME; >> if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_FP)) >> state->available_types |= UNWIND_USER_TYPE_FP; >> + if (IS_ENABLED(CONFIG_HAVE_UNWIND_USER_BACKCHAIN)) >> + state->available_types |= UNWIND_USER_TYPE_BACKCHAIN; > > Any reason not to just use the existing CONFIG_HAVE_UNWIND_USER_FP hook > here rather than create the new BACKCHAIN one? At first I thought this would not be a good idea, as my unwind user backchain implementation relies on being standalone without using unwind_user_next_common(). Mainly because s390 back chain unwinding does not have fixed CFA, FP, and RA offsets/locations. But then I gave it a try and it does not look that bad actually. I'll send a RFC v3 soon. Regards, Jens -- Jens Remus Linux on Z Development (D3303) +49-7031-16-1128 Office jremus@de.ibm.com IBM IBM Deutschland Research & Development GmbH; Vorsitzender des Aufsichtsrats: Wolfgang Wendt; Geschäftsführung: David Faller; Sitz der Gesellschaft: Böblingen; Registergericht: Amtsgericht Stuttgart, HRB 243294 IBM Data Privacy Statement: https://www.ibm.com/privacy/