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Fri, 13 Dec 2024 19:13:06 -0800 (PST) Received: from [192.168.0.235] ([38.34.87.7]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-218a1db8676sm4573285ad.12.2024.12.13.19.13.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Dec 2024 19:13:06 -0800 (PST) Message-ID: <31b0c85dbf85486df116ade20caf8685843899b4.camel@gmail.com> Subject: Re: [PATCH bpf-next v5 4/5] bpf: verifier: Support eliding map lookup nullness From: Eduard Zingerman To: Daniel Xu , Andrii Nakryiko Cc: andrii@kernel.org, ast@kernel.org, shuah@kernel.org, daniel@iogearbox.net, john.fastabend@gmail.com, martin.lau@linux.dev, song@kernel.org, yonghong.song@linux.dev, kpsingh@kernel.org, sdf@fomichev.me, haoluo@google.com, jolsa@kernel.org, mykolal@fb.com, bpf@vger.kernel.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, netdev@vger.kernel.org Date: Fri, 13 Dec 2024 19:13:00 -0800 In-Reply-To: References: <92065ca054beccd6d0f35efe9715ef965e8d379f.1734045451.git.dxu@dxuuu.xyz> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.54.1 (3.54.1-1.fc41) Precedence: bulk X-Mailing-List: linux-kselftest@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Fri, 2024-12-13 at 19:44 -0700, Daniel Xu wrote: [...] > > > + /* First handle precisely tracked STACK_ZERO, up to BPF_REG_S= IZE */ > > > + stype =3D state->stack[spi].slot_type; > > > + for (i =3D 0; i < BPF_REG_SIZE && stype[i] =3D=3D STACK_ZERO;= i++) > >=20 > > it's Friday and I'm lazy, but please double-check that this works for > > both big-endian and little-endian :) >=20 > Any tips? Are the existing tests running thru s390x hosts in CI > sufficient or should I add some tests writen in C (and not BPF > assembler)? I can never think about endianness correctly... I think that if test operates on a key like: valid key 15 v 0000000f <-- written to stack as a single u64 value ^^^^^^^ stack zero marks and is executed (e.g. using __retval annotation), then CI passing for s390 should be enough. There is a guide on how to gen a s390 environment locally: https://docs.kernel.org/bpf/s390.html I used it recently to build a vmlinux for s390 with no or minimal issues. Used it to boot long time ago, but don't remember if there were any surprises. > > with Eduard's suggestion this also becomes interesting when you have > > 000mmm mix (as one example), because that gives you a small range, and > > all values might be valid keys for arrays >=20 > Can you define what "small range" means? What range is there with 0's? > Any pointers would be helpful. I think Andrii means that each 'm' adds 8 bits of range. E.g. range for 0000_000m is 0-255, range for 0000_00mm is 0-65535, etc. [...]