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Mon, 28 Aug 2023 06:54:21 -0700 (PDT) From: Jiri Olsa X-Google-Original-From: Jiri Olsa Date: Mon, 28 Aug 2023 15:54:18 +0200 To: Rong Tao Cc: olsajiri@gmail.com, alexandre.torgue@foss.st.com, andrii@kernel.org, ast@kernel.org, bpf@vger.kernel.org, chantr4@gmail.com, daniel@iogearbox.net, deso@posteo.net, eddyz87@gmail.com, haoluo@google.com, iii@linux.ibm.com, john.fastabend@gmail.com, kpsingh@kernel.org, laoar.shao@gmail.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-stm32@st-md-mailman.stormreply.com, martin.lau@linux.dev, mcoquelin.stm32@gmail.com, mykolal@fb.com, rongtao@cestc.cn, sdf@google.com, shuah@kernel.org, song@kernel.org, xukuohai@huawei.com, yonghong.song@linux.dev, zwisler@google.com Subject: Re: [PATCH bpf-next v8] selftests/bpf: trace_helpers.c: optimize kallsyms cache Message-ID: References: MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20230828_065426_112987_EDA6DAD0 X-CRM114-Status: GOOD ( 24.71 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Mon, Aug 28, 2023 at 08:57:21AM +0800, Rong Tao wrote: > Hi, jirka. Thanks for your reply. > > > > @@ -164,13 +165,14 @@ int main(int argc, char **argv) > > > } > > > > > > /* initialize kernel symbol translation */ > > > - if (load_kallsyms()) { > > > + ksyms = load_kallsyms(); > > > > if we keep the load_kallsyms/ksym_search/ksym_get_addr functions as described > > in [1] the samples/bpf would stay untouched apart from the Makefile change > > Maybe we should make this modification, wouldn't it be better? After all, > not modifying the source code of samples/bpf is not really a reason not to > make modifications to load_kallsyms(), what do you think? I think we want separate selftest and samples changes and I don't see other way to do that > > In addition, if we continue to keep the original ksym_search() interface, > the following problems are very difficult to deal with: > > Source code ksym_search [1] > > struct ksym *ksym_search(long key) > { > int start = 0, end = sym_cnt; > int result; > > /* kallsyms not loaded. return NULL */ > if (sym_cnt <= 0) > return NULL; > > while (start < end) { > size_t mid = start + (end - start) / 2; > > result = key - syms[mid].addr; > if (result < 0) > end = mid; > else if (result > 0) > start = mid + 1; > else > return &syms[mid]; <<< > } > > if (start >= 1 && syms[start - 1].addr < key && > key < syms[start].addr) > /* valid ksym */ > return &syms[start - 1]; <<< > > /* out of range. return _stext */ > return &syms[0]; <<< > } > > The original ksym_search() interface directly returns the global syms > address, which is also dangerous for multi-threading. If we allocate new > memory for this, it is not a perfect solution. the assumption was that the original ksym_search touches the global syms allocated before running tests.. then tests that actually need fresh kallsyms data (because of bpf_testmod load/unload) would get their own copy of kallsyms jirka > > If we rewrite > > struct ksym *ksym_search(long key) > > to > struct ksym ksym_search(long key) > > This also affects the source code in samples/bpf. > > The same problem exists with ksym_get_addr(). > > Best wishes, > Rong Tao > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git/tree/tools/testing/selftests/bpf/trace_helpers.c#n100 > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel