From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mathieu Desnoyers Subject: Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT Date: Tue, 27 Mar 2018 20:44:12 -0400 (EDT) Message-ID: <1513083686.1804.1522197852512.JavaMail.zimbra@efficios.com> References: <20180327024706.2064725-1-ast@fb.com> <20180327130211.284c8924@gandalf.local.home> <20180327131143.4b83534c@gandalf.local.home> <20180327145824.602dfdec@gandalf.local.home> <20180327170438.77c0f8fd@gandalf.local.home> <563f7fa0-5fea-00d3-1eb3-fa00d8cf7e29@fb.com> <430531879.1792.1522192417816.JavaMail.zimbra@efficios.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: rostedt , "David S. Miller" , Daniel Borkmann , Linus Torvalds , Peter Zijlstra , netdev , kernel-team , linux-api , Kees Cook To: Alexei Starovoitov Return-path: Received: from mail.efficios.com ([167.114.142.138]:52516 "EHLO mail.efficios.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752779AbeC1AoO (ORCPT ); Tue, 27 Mar 2018 20:44:14 -0400 In-Reply-To: Sender: netdev-owner@vger.kernel.org List-ID: ----- On Mar 27, 2018, at 8:00 PM, Alexei Starovoitov ast@fb.com wrote: > On 3/27/18 4:13 PM, Mathieu Desnoyers wrote: >> ----- On Mar 27, 2018, at 6:48 PM, Alexei Starovoitov ast@fb.com wrote: >> >>> On 3/27/18 2:04 PM, Steven Rostedt wrote: >>>> >>>> +#ifdef CONFIG_BPF_EVENTS >>>> +#define BPF_RAW_TP() . = ALIGN(8); \ >> >> Given that the section consists of a 16-bytes structure elements >> on architectures with 8 bytes pointers, this ". = ALIGN(8)" should >> be turned into a STRUCT_ALIGN(), especially given that the compiler >> is free to up-align the structure on 32 bytes. > > STRUCT_ALIGN fixed the 'off by 8' issue with kasan, > but it fails without kasan too. > For some reason the whole region __start__bpf_raw_tp - __stop__bpf_raw_tp > comes inited with cccc: > [ 22.703562] i 1 btp ffffffff8288e530 btp->tp cccccccccccccccc func > cccccccccccccccc > [ 22.704638] i 2 btp ffffffff8288e540 btp->tp cccccccccccccccc func > cccccccccccccccc > [ 22.705599] i 3 btp ffffffff8288e550 btp->tp cccccccccccccccc func > cccccccccccccccc > [ 22.706551] i 4 btp ffffffff8288e560 btp->tp cccccccccccccccc func > cccccccccccccccc > [ 22.707503] i 5 btp ffffffff8288e570 btp->tp cccccccccccccccc func > cccccccccccccccc > [ 22.708452] i 6 btp ffffffff8288e580 btp->tp cccccccccccccccc func > cccccccccccccccc > [ 22.709406] i 7 btp ffffffff8288e590 btp->tp cccccccccccccccc func > cccccccccccccccc > [ 22.710368] i 8 btp ffffffff8288e5a0 btp->tp cccccccccccccccc func > cccccccccccccccc > > while gdb shows that everything is good inside vmlinux > for exactly these addresses. > Some other linker magic missing? No, Steven's iteration code is incorrect. +extern struct bpf_raw_event_map __start__bpf_raw_tp; +extern struct bpf_raw_event_map __stop__bpf_raw_tp; That should be: extern struct bpf_raw_event_map __start__bpf_raw_tp[]; extern struct bpf_raw_event_map __stop__bpf_raw_tp[]; + +struct bpf_raw_event_map *bpf_find_raw_tracepoint(const char *name) +{ + const struct bpf_raw_event_map *btp = &__start__bpf_raw_tp; const struct bpf_raw_event_map *btp = __start__bpf_raw_tp; + int i = 0; + + for (; btp < &__stop__bpf_raw_tp; btp++) { for (; btp < __stop__bpf_raw_tp; btp++) { Those start/stop symbols are given their address by the linker automatically (this is a GNU linker extension). We don't want pointers to the symbols, but rather the symbols per se to act as start/stop addresses. Thanks, Mathieu + i++; + if (!strcmp(btp->tp->name, name)) + return btp; + } + return NULL; +} -- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com