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([2620:10d:c090:500::7:ac0c]) by smtp.gmail.com with ESMTPSA id 46e09a7af769-81604bae8cdsm3696386a34.27.2026.09.23.11.06.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 23 Sep 2026 11:06:09 -0700 (PDT) Message-ID: <0c312ad4f725193e714a50c5fcfc31ad2b273f7d.camel@gmail.com> Subject: Re: [PATCH bpf-next v5 07/21] bpf: Explore the landing pads no call site reaches From: Eduard Zingerman To: Yonghong Song , bpf@vger.kernel.org Cc: Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , kernel-team@fb.com Date: Wed, 23 Sep 2026 11:06:07 -0700 In-Reply-To: <3469ede8-6c37-49c9-b261-d2c8506eada5@linux.dev> References: <20260923045846.2414643-1-yonghong.song@linux.dev> <20260923045922.2417689-1-yonghong.song@linux.dev> <3469ede8-6c37-49c9-b261-d2c8506eada5@linux.dev> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.60.2 (3.60.2-1.fc44) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Wed, 2026-09-23 at 10:27 -0700, Yonghong Song wrote: ... > This patch is to avoid a verification failure. Let us say, we remove this > patch and run the following > ./test_progs -t exceptions_cleanup > and we will get the following failure: ... > This patch intends to explore *unreachable* insns to avoid verification f= ailure. > > I think due to "record =3D { begin =3D 1, end =3D 2, pad =3D 4 }", it is = considered that the code at 'pad =3D 4' > is not dead, but actually it does dead later so we have the above failure= . > > So I add this patch to avoid failure. But maybe we should just remove thi= s patch, > and mark this test as failure as indeed landing pad is not reachable. > > WDYT? But that's a self-fulfilling thing, the test you are pointing at looks as follows: /* * 15. A region around a call the kernel knows cannot unwind: no call site= is * marked, nothing reaches the pad, and the sweep removes it. The program = is * otherwise ordinary and has to load. */ static __used __naked __noinline __u64 nounwind_rec_frame(void) { ... } So, the test is added to test this cfg pass, the cfg pass is added to make this test pass, meanwhile compiler does not generate such code. I don't see a point, tbh.