Messages in this thread | | | Subject | Re: perf test BPF failing on f24: fix | From | "Wangnan (F)" <> | Date | Wed, 3 Aug 2016 11:41:59 +0800 |
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On 2016/8/3 10:41, Wangnan (F) wrote: > > > 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@jouet ~]# grep -i sys_epoll_wait /proc/kallsyms >> ffffffffbd295b50 T SyS_epoll_wait >> ffffffffbd295b50 T sys_epoll_wait >> [root@jouet ~]# >> >> I noticed that it is some sort of aliasing so I checked the other >> variant: >> >> [root@jouet ~]# 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@jouet ~]# > > 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@jouet ~]# 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. >
Still unable reproduce. I tried tip/core/core, which is '4.7.0+'. I also turns off CONFIG_DEBUG_INFO. In this case, testcase BPF prologue fails as expected, and basic BPF test is okay.
After removing vmlinux, with kallsyms information 'perf probe sys_epoll_wait' sets only 1 kprobe, but it still works.
I think there is a bug in your vmlinux. Could you please do a bisect to find which commit causes this problem?
Thank you.
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