From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: Re: [PATCH v6 bpf-next 08/11] bpf: introduce BPF_RAW_TRACEPOINT Date: Tue, 27 Mar 2018 17:51:55 -0700 Message-ID: <34b9892d-c091-7b83-d8e8-79c0ff813140@fb.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> <1513083686.1804.1522197852512.JavaMail.zimbra@efficios.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1513083686.1804.1522197852512.JavaMail.zimbra@efficios.com> Sender: netdev-owner@vger.kernel.org To: Mathieu Desnoyers Cc: rostedt , "David S. Miller" , Daniel Borkmann , Linus Torvalds , Peter Zijlstra , netdev , kernel-team , linux-api , Kees Cook List-Id: linux-api@vger.kernel.org On 3/27/18 5:44 PM, Mathieu Desnoyers wrote: > ----- 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. right. that part I fixed first. Turned out it was in init.data section and got poisoned. this fixes it: @@ -258,6 +258,7 @@ LIKELY_PROFILE() \ BRANCH_PROFILE() \ TRACE_PRINTKS() \ + BPF_RAW_TP() \ TRACEPOINT_STR() /* @@ -585,7 +586,6 @@ *(.init.rodata) \ FTRACE_EVENTS() \ TRACE_SYSCALLS() \ - BPF_RAW_TP() \ KPROBE_BLACKLIST() \ ERROR_INJECT_WHITELIST() \ MEM_DISCARD(init.rodata) \ and it works :) I will clean few other nits I found while debugging and respin.