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a=qoll8+KPOyaMroiJ2sR5sw==:17 a=6eWqkTHjU83fiwn7nKZWdM+Sl24=:19 a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=6UeiqGixMTsA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=VwQbUJbxAAAA:8 a=OPC_c1hGrdcbYSRWtHAA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 cc=ntf awl=host:12099 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMSBTYWx0ZWRfX7GHAbEzpGmRQ /K/8Oe35f8X0VvEGRNxrfqp0S3joI2qD/2LCLXYH2/U2+O1NQsTrAa7z2EIkmTMYo56qShDYmPV n0WTaSk3f/OkxkVbXsNgYBbBWHNgb1hFTUmoSn5WS+6S6P7I+wg45siMx31UqENDWgAQz39Hu24 zaKflBzz8yV1U5yXKn74R/5U62H19TvSoOen8yJZVMQ/q67DSVNm4At5egdS1Lz3hueojq8Xwis LMMTSnzb8XyM/yCdPZJF+1v6qsQig7iW0ItVv9LfcE5R1z3kQVBueaGEFDeXwENPW1Qgo48o1BJ NmTNtqoHPo/05Ve5Y/jb9s33cWqeh8o/PliSTTh4U7Z2yhK23LNosmCMuI5gzYX4N5MaqEOYr// jZ0AvUIvX+I6FkYog3PIJK3B9GxlEAkfUesH6F2+BmIKhExiKH8= On 11/17/25 4:49 PM, Puranjay Mohan wrote: > On Tue, Nov 18, 2025 at 1:10 AM Josh Poimboeuf wrote: >> >> On Mon, Nov 17, 2025 at 06:42:23PM -0500, Steven Rostedt wrote: >>> On Mon, 17 Nov 2025 15:06:32 -0800 >>> Josh Poimboeuf wrote: >>> >>>> The ORC unwinder marks the unwind "unreliable" if it has to fall back to >>>> frame pointers. >>>> >>>> But that's not a problem for livepatch because it only[*] unwinds >>>> blocked/sleeping tasks, which shouldn't have BPF on their stack anyway. >>>> >>>> [*] with one exception: the task calling into livepatch >>> >>> It may be a problem with preempted tasks right? I believe with PREEMPT_LAZY >>> (and definitely with PREEMPT_RT) BPF programs can be preempted. >> >> In that case, then yes, that stack would be marked unreliable and >> livepatch would have to go try and patch the task later. >> >> If it were an isolated case, that would be fine, but if BPF were >> consistently on the same task's stack, it could stall the completion of >> the livepatch indefinitely. >> >> I haven't (yet?) heard of BPF-induced livepatch stalls happening in >> reality, but maybe it's only a matter of time :-/ >> >> To fix that, I suppose we would need some kind of dynamic ORC >> registration interface. Similar to what has been discussed with >> sframe+JIT. > > I work with the BPF JITs and would be interested in exploring this further, > can you point me to this discussion if it happened on the list. > We discussed SFrame/JIT topic earlier this year in our monthly SFrame meetings. I can point you to the meeting notes in a separate email. We had some discussion around: - SFrame specification: Allow efficient addition, removal and update of data in SFrame sections. A part of the challenge is in representing the variety of frames a JIT may use. - SFrame APIs with JIT: Efficient SFrame stack trace data manipulation by JIT. - Interface with Linux kernel: Efficient SFrame stack trace data registration and update stack trace data. It will be great to have more collaboration and brainstorming, and to include BPF/JIT in the discussions. >> >> If BPF were to always use frame pointers then there would be only a very >> limited set of ORC entries (either "frame pointer" or "undefined") for a >> given BPF function and it shouldn't be too complicated. >> >> -- >> Josh