Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754515AbbGWCkP (ORCPT ); Wed, 22 Jul 2015 22:40:15 -0400 Received: from szxga02-in.huawei.com ([119.145.14.65]:24048 "EHLO szxga02-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753818AbbGWCkN (ORCPT ); Wed, 22 Jul 2015 22:40:13 -0400 Message-ID: <55B053FE.90808@huawei.com> Date: Thu, 23 Jul 2015 10:39:58 +0800 From: xiakaixu User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:17.0) Gecko/20130801 Thunderbird/17.0.8 MIME-Version: 1.0 To: Alexei Starovoitov CC: , , , , , , , , , Subject: Re: [PATCH v2 4/5] bpf: Implement function bpf_perf_event_read() that get the selected hardware PMU conuter References: <1437552572-84748-1-git-send-email-xiakaixu@huawei.com> <1437552572-84748-5-git-send-email-xiakaixu@huawei.com> <55B04003.3000904@plumgrid.com> <55B04DA5.6020807@huawei.com> <55B04FEB.4090800@plumgrid.com> In-Reply-To: <55B04FEB.4090800@plumgrid.com> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.111.101.23] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1658 Lines: 53 于 2015/7/23 10:22, Alexei Starovoitov 写道: > On 7/22/15 7:12 PM, xiakaixu wrote: >> So you mean like this? >> >> u64 bpf_perf_event_read(u64 r1, u64 index,...) >> { >> struct bpf_perf_event_array *array = (void *) (long) r1; >> struct perf_event *event; >> ... >> event = array->events[index]; >> ... >> } > > yes. the only thing needed is to add: > if (index >= array->map.max_entries) > return -E2BIG; > before accessing array->events[index]; > >>> > >>>> >>+const struct bpf_func_proto bpf_perf_event_read_proto = { >>>> >>+ .func = bpf_perf_event_read, >>>> >>+ .gpl_only = false, >>>> >>+ .ret_type = RET_INTEGER, >>>> >>+ .arg1_type = ARG_CONST_MAP_PTR, >>>> >>+ .arg2_type = ARG_PTR_TO_MAP_KEY, >>> > >>> >make it arg2_type = ARG_ANYTHING then you'll just index >>> >into array the way prog_array does and similar to bpf_tail_call. > >> ARG_ANYTHING means any (initialized) argument is ok, but we here > > correct. > >> really want is map key. So I'm not sure ARG_ANYTHING is suitable. >> You know ARG_ANYTHING is not checked enough in verifier. > > why? during perf_event_array creation time we check that key_size == u32 > so we can accept any integer. > ARG_PTR_TO_MAP_KEY forces program author to use stack instead of > passing index directly. Direct index is obviously faster. Copy that. We will follow them in V3. > > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/