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Fri, 02 Oct 2026 04:48:43 -0700 (PDT) Content-Type: text/plain; charset=UTF-8 Date: Fri, 02 Oct 2026 11:48:42 +0000 Message-Id: Cc: "Alan Maguire" , "Martin KaFai Lau" , "Yonghong Song" , "Jiri Olsa" , "Ihor Solodrai" , "Quentin Monnet" , "Nathan Chancellor" , "Nicolas Schier" , , =?utf-8?q?Thomas_Wei=C3=9Fschuh?= , "Christian Heusel" , "Luis Chamberlain" , "Petr Pavlu" , "Sami Tolvanen" , , "Steven Rostedt" , "Masami Hiramatsu" , "Mathieu Desnoyers" , , "Arnaldo Carvalho de Melo" , "Namhyung Kim" , "Ian Rogers" , , "Jiri Kosina" , "Benjamin Tissoires" , , "Tejun Heo" , "David Vernet" , "Andrea Righi" , "Changwoo Min" , , "Shuah Khan" , , "Miguel Ojeda" , , "Arnd Bergmann" , , , "Hazem Mohamed Abuelfotoh" , "Bjoern Doebel" , "Martin Pohlack" , Subject: Re: [PATCH bpf-next v4 04/12] bpf: take the vmlinux BTF from the btf_vmlinux module From: "Alexei Starovoitov" To: "Jay Wang" , , "Daniel Borkmann" , "Andrii Nakryiko" , "Eduard Zingerman" , "Kumar Kartikeya Dwivedi" In-Reply-To: <20261001225214.12351-5-wanjay@amazon.com> References: <20261001225214.12351-1-wanjay@amazon.com> <20261001225214.12351-5-wanjay@amazon.com> X-Mailer: mkdraft (claude review draft; edit before sending) Content-Transfer-Encoding: 8bit Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 On Thu, Oct 01, 2026 at 10:52 PM Jay Wang wrote: > + err = __sys_bpf(cmd, USER_BPFPTR(uattr), size, USER_BPFPTR(uattr_common), size_common); > + if (IS_MODULE(CONFIG_DEBUG_INFO_BTF) && err < 0 && bpf_btf_vmlinux_retry(cmd, misses)) > + err = __sys_bpf(cmd, USER_BPFPTR(uattr), size, USER_BPFPTR(uattr_common), > + size_common); Running the command twice when it failed and a global counter moved is not going to fly. Missing BTF is not always an error. With =m and BTF not loaded yet take int prog(struct xdp_md *ctx) with func_info. That is everything libbpf loads. do_check_common() calls btf_prepare_func_args(env, 0). find_canonical_prog_ctx_type() returns NULL, btf_is_prog_ctx_type() returns false, the arg becomes ARG_PTR_TO_MEM and func_info_aux[0].unreliable is set. The prog loads. err == 0. No retry. >From then on freplace of that prog fails with "Cannot replace static functions" and fentry/fexit see its args as scalars, even after BTF is loaded. With =y both work. That is the only reason why "a socket filter does not load it". In v3 such prog loaded BTF. systemd built with BPF_FRAMEWORK loads int sd_bind4(struct bpf_sock_addr *ctx) from manager_setup_cgroup() at every boot. The result of the verification cannot depend on who touched BTF first. bpf-ci is right too. The first run writes into uattr. It's starting to feel that this is dead end. So much complexity to save few Mbyte. pw-bot: cr