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Wed, 28 Oct 2026 17:27:59 -0700 (PDT) Received: from localhost ([153.61.198.254]) by smtp.gmail.com with ESMTPSA id 98e67ed59e1d1-3ae6e874bebsm1414510a91.14.2026.10.28.17.27.58 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 28 Oct 2026 17:27:58 -0700 (PDT) X-Mailing-List: bpf@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Thu, 29 Oct 2026 00:27:58 +0000 Message-Id: Cc: , , , Subject: Re: [PATCH bpf 26/81] bpf: Support BPF_REG_ARENA_SP in the verifier From: "Alexei Starovoitov" To: "Kumar Kartikeya Dwivedi" X-Mailer: aerc 0.20.1-349-gb940a4174a3e-dirty References: <20261026025943.404450-1-alexei.starovoitov@gmail.com> <20261026025943.404450-27-alexei.starovoitov@gmail.com> In-Reply-To: On Thu Oct 29, 2026 at 12:07 AM UTC, Kumar Kartikeya Dwivedi wrote: > On Wed, 28 Oct 2026 at 20:01, Alexei Starovoitov > wrote: >> >> On Wed, Oct 28, 2026 at 04:00 AM Kumar Kartikeya Dwivedi wrote: >> > Sigh. This is not a good response. If you do not want to have a >> > discussion, what is the point of posting patches and asking for >> > feedback? >> >> I do want the discussion. That's why parts 2 and 3 were posted for feedb= ack. >> >> Maybe I missed, but so far I didn't hear an alternative proposal. > > I was not making a proposal. I don't even understand half the changes > yet, it's a long series (81 minus 16 patches), and I haven't been able > to digest it yet in 3 days. The only thing I was trying to understand > was the motivation for the split stack, and it wasn't (still isn't) > clear to me why it's necessary. That's why the first thing in the cover letter: " Where to start =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D Patch 69 rewrites Documentation/bpf/verifier.rst. It explains the algorithm with 11 examples. Read it first. Then read patches 47, 52 and 53: the join of two states, the new main pass, and the switch to it. " Re: stack-in-arena. rust routinely needs 32k and in one create it needs 65k. The kernel stack cannot support it. private stack, the way it is today, doesn't work either, since it's non-recursive, but recursion is necessary. >> Only worries and concerns and "there must be some way". >> I expored all ways I could think of and listed some of them in prior ema= il. >> If you have a sketch of not a 'stack in arena' approach, I'm all hears. > > I think it will take time to understand and reason about all this. > Decisions on where to place .rodata, how that interacts with the > examples you showed, how the verifier works now, what the compiler is > doing differently... > > But if we don't want to wait, and you feel you have already explored > the solution space and all of this seems fine to you, it would be > wasted effort on my part. So we can continue with what you have. Not quite. _We_ don't have time to wait. If you're saying: I _have_ to spend a week to read the patches before I can discuss it, then yeah we're not on the same page. I'm asking to do 'Where to start' section. It will take an hour. Maybe two. verifier.rst and commit logs of these 3 patches are well rewritten and easy to understand. They are enough to have the discussion. *now*. We might throw away all of it, so spending a week to read the patches is a waste of time. Do not do it.