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Tue, 22 Apr 2025 14:07:38 -0700 (PDT) Received: from ezingerman-mba ([2620:10d:c090:500::6:9822]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22c50eb4622sm90017845ad.108.2025.04.22.14.07.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 22 Apr 2025 14:07:38 -0700 (PDT) From: Eduard Zingerman To: Kumar Kartikeya Dwivedi Cc: bpf@vger.kernel.org, Alexei Starovoitov , Andrii Nakryiko , Daniel Borkmann , Martin KaFai Lau , Emil Tsalapatis , Barret Rhoden , kkd@meta.com, kernel-team@meta.com Subject: Re: [RFC PATCH bpf-next/net v1 08/13] bpf: Add dump_stack() analogue to print to BPF stderr In-Reply-To: <20250414161443.1146103-9-memxor@gmail.com> (Kumar Kartikeya Dwivedi's message of "Mon, 14 Apr 2025 09:14:38 -0700") References: <20250414161443.1146103-1-memxor@gmail.com> <20250414161443.1146103-9-memxor@gmail.com> Date: Tue, 22 Apr 2025 14:07:35 -0700 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Precedence: bulk X-Mailing-List: bpf@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Kumar Kartikeya Dwivedi writes: > Introduce a kernel function which is the analogue of dump_stack() > printing some useful information and the stack trace. This is not > exposed to BPF programs yet, but can be made available in the future. > > When we have a PC for a BPF program in the stack trace, also > additionally output the filename and line number to make the trace > helpful. The rest of the trace can be passed into ./decode_stacktrace.sh > to obtain the line numbers for kernel symbols. > > Signed-off-by: Kumar Kartikeya Dwivedi > --- Seems to work as advertised. Reviewed-by: Eduard Zingerman [...] > +static int dump_stack_bpf_linfo(u64 ip, const char **filep) > +{ > + struct bpf_prog *prog = bpf_prog_ksym_find(ip); > + int idx = -1, insn_start, insn_end, len; > + struct bpf_line_info *linfo; > + void **jited_linfo; > + struct btf *btf; > + > + btf = prog->aux->btf; > + linfo = prog->aux->linfo; > + jited_linfo = prog->aux->jited_linfo; > + > + if (!btf || !linfo || !prog->aux->jited_linfo) > + return -1; > + len = prog->aux->func ? prog->aux->func[prog->aux->func_idx]->len : prog->len; > + > + linfo = &prog->aux->linfo[prog->aux->linfo_idx]; > + jited_linfo = &prog->aux->jited_linfo[prog->aux->linfo_idx]; > + > + insn_start = linfo[0].insn_off; > + insn_end = insn_start + len; > + > + for (int i = 0; linfo[i].insn_off >= insn_start && linfo[i].insn_off < insn_end; i++) { > + if (jited_linfo[i] >= (void *)ip) > + break; > + idx = i; > + } > + > + if (idx == -1) > + return -1; > + > + *filep = btf_name_by_offset(btf, linfo[idx].file_name_off); > + *filep = strrchr(*filep, '/') ?: *filep; > + *filep += 1; Nit: `+= 1` not needed if '/' was not found? > + > + return BPF_LINE_INFO_LINE_NUM(linfo[idx].line_col); > +} [...]