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Date: Wed, 3 Aug 2016 10:41:51 +0800 From: "Wangnan (F)" <wangnan0@...wei.com> To: Arnaldo Carvalho de Melo <acme@...nel.org> CC: Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: perf test BPF failing on f24: fix On 2016/8/3 3:51, Arnaldo Carvalho de Melo wrote: > Hi Wang, > > Something changed and a function used in a perf test for BPF is > not anymore appearing on vmlinux, albeit still available on > /proc/kallsyms: > > # readelf -wi /lib/modules/4.7.0+/build/vmlinux | grep -w sys_epoll_wait > # > > But: > > [root@...et ~]# grep -i sys_epoll_wait /proc/kallsyms > ffffffffbd295b50 T SyS_epoll_wait > ffffffffbd295b50 T sys_epoll_wait > [root@...et ~]# > > I noticed that it is some sort of aliasing so I checked the other > variant: > > [root@...et ~]# readelf -wi /lib/modules/4.7.0+/build/vmlinux | grep -w SyS_epoll_wait > <2bc9b85> DW_AT_name : (indirect string, offset: 0xe7524): SyS_epoll_wait > [root@...et ~]# I also see no sys_epoll_wait in output of 'readelf -wi', but I can't reproduce the whole problem. > Trying to use perf probe also produces the same resuls I notice when > running the perf test that is failing: > > [root@...et ~]# perf probe sys_epoll_wait > Failed to find debug information for address ffffffffbd295b50 > Probe point 'sys_epoll_wait' not found. > Error: Failed to add events. For me: # uname -r 4.7.0 # perf probe -v sys_epoll_wait probe-definition(0): sys_epoll_wait symbol:sys_epoll_wait file:(null) line:0 offset:0 return:0 lazy:(null) 0 arguments Looking at the vmlinux_path (8 entries long) Using /lib/modules/4.7.0/build/vmlinux for symbols Open Debuginfo file: /lib/modules/4.7.0/build/vmlinux Try to find probe point from debuginfo. Symbol sys_epoll_wait address found : ffffffff81281240 Matched function: SyS_epoll_wait found inline addr: 0xffffffff81281240 Probe point found: SyS_epoll_wait+0 found inline addr: 0xffffffff812813a7 Probe point found: SyS_epoll_pwait+135 found inline addr: 0xffffffff8128157a Probe point found: compat_SyS_epoll_pwait+154 Found 3 probe_trace_events. Opening /sys/kernel/debug/tracing//kprobe_events write=1 Writing event: p:probe/sys_epoll_wait _text+2626112 Writing event: p:probe/sys_epoll_wait_1 _text+2626471 Writing event: p:probe/sys_epoll_wait_2 _text+2626938 Added new events: probe:sys_epoll_wait (on sys_epoll_wait) probe:sys_epoll_wait_1 (on sys_epoll_wait) probe:sys_epoll_wait_2 (on sys_epoll_wait) You can now use it in all perf tools, such as: perf record -e probe:sys_epoll_wait_2 -aR sleep 1 I'll try different kernel version and kconfig. Thank you.
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