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Tue, 03 Mar 2026 13:43:19 +0000 Received: from smtpav05.fra02v.mail.ibm.com (smtpav05.fra02v.mail.ibm.com [10.20.54.104]) by smtprelay03.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 623DhFIF55443728 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Tue, 3 Mar 2026 13:43:15 GMT Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 872F220043; Tue, 3 Mar 2026 13:43:15 +0000 (GMT) Received: from smtpav05.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 1A6BE20040; Tue, 3 Mar 2026 13:43:14 +0000 (GMT) Received: from [9.78.106.17] (unknown [9.78.106.17]) by smtpav05.fra02v.mail.ibm.com (Postfix) with ESMTP; Tue, 3 Mar 2026 13:43:13 +0000 (GMT) Message-ID: <30d026c1-5d0d-4679-95e3-cd39b670d353@linux.ibm.com> Date: Tue, 3 Mar 2026 19:13:13 +0530 X-Mailing-List: linuxppc-dev@lists.ozlabs.org List-Id: List-Help: List-Owner: List-Post: List-Archive: , List-Subscribe: , , List-Unsubscribe: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 3/5] powerpc64/bpf: use consistent tailcall offset in trampoline To: adubey Cc: linuxppc-dev , bpf@vger.kernel.org, Madhavan Srinivasan , Alexei Starovoitov , Daniel Borkmann , Andrii Nakryiko , Saket Kumar Bhaskar , Venkat Rao Bagalkote References: <20260220063933.196141-1-hbathini@linux.ibm.com> <20260220063933.196141-4-hbathini@linux.ibm.com> <2f33ecbbe8272184111c5406d167b6b0@linux.ibm.com> Content-Language: en-US From: Hari Bathini In-Reply-To: <2f33ecbbe8272184111c5406d167b6b0@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-GUID: l8VTyG3UgxY0iVvA9BQnq-bN8x8KDGvE X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzAzMDEwOCBTYWx0ZWRfX1ACPhmQcCAiT oboLBiA+Cq5tWxASWZaqkePBcKKpJ2UaQ7A9ZblPQmdqCKMY6yeBSK40mIEBT4qp+Ysk9Ojsw4c aMId/5GOGkZ8nErDbqMVoy6NUt6wrfM4jZBoydYdWb+fa3FAQ1C6hdln+PuKi2vr7vuqiP42Fvq +d/BpneEi3NUJlBMhSLm8MlE86hUNSKpGLWmnqVuSWsOFMKNujoqM5iYZbJD/NwjcDjblKEryLV Fnc69W3ZpSzQ+VUcuf7nUN4ZxEe1tvfaSz9o3/5AisE3r3mmc8xZZhrDRRQrLAD22Is+SJq1ORK QbyPRnsp+J8+if+/2+pCbEOJUOAcx6EWI8+UbrRKFD/PuCyjstohZCwOCQVnRrOVEm2j/D7mxto vmaV4Zhm/EOPqPiTP40jJ3jWwflPuCvC1d8uzAT+r/SRXxCAKPURPpl8oG7PyuHIo/o+/5P+9W+ 0SnCjGlt2rk8EKuuL3g== X-Authority-Analysis: v=2.4 cv=H7DWAuYi c=1 sm=1 tr=0 ts=69a6e578 cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=hklsHozHma9wGV9YwB4A:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: l8VTyG3UgxY0iVvA9BQnq-bN8x8KDGvE X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-02_05,2026-03-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 impostorscore=0 suspectscore=0 phishscore=0 clxscore=1015 priorityscore=1501 adultscore=0 bulkscore=0 spamscore=0 malwarescore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603030108 On 22/02/26 6:37 pm, adubey wrote: > On 2026-02-20 12:09, Hari Bathini wrote: >> Ideally, the offset used to load the tail call info field and to find >> the pass by reference address for tail call field should be the same. >> But while setting up the tail call info in the trampoline, this was >> not followed. This can be misleading and can lead to unpredictable >> results if and when bpf_has_stack_frame() ends up returning true >> for trampoline frame. Since commit 15513beeb673 ("powerpc64/bpf: >> Moving tail_call_cnt to bottom of frame") and commit 2ed2d8f6fb38 >> ("powerpc64/bpf: Support tailcalls with subprogs") ensured tail call >> field is at the bottom of the stack frame for BPF programs as well as >> BPF trampoline, avoid relying on bpf_jit_stack_tailcallinfo_offset() >> and bpf_has_stack_frame() for trampoline frame and always calculate >> tail call field offset with reference to older frame. > > It's good to add comment about padding field placed after tailcall_info > in the trampoline stack layout. Visibly padding is following tailcall_info > but tailcall_info is bottom-most field. Clear comment around this > will be really helpful. "Generated stack layout:" does capture that clearly. Don't find it relevant to explain it again in this context.. - Hari