Messages in this thread | | | Date | Tue, 2 Aug 2016 23:15:34 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: perf test BPF failing on f24: fix |
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Em Tue, Aug 02, 2016 at 02:03:33PM -0700, Alexei Starovoitov escreveu: > On Tue, Aug 02, 2016 at 04:51:02PM -0300, 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 ~]# > > > > 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. > > [root@jouet ~]# perf probe SyS_epoll_wait > > 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) > > that change will break all sorts of scripts that relying on syscalls to start > with sys_
Is there a promise that internal kernel functions will not change names?
> I guess we can workaround in user space, but what was the motivation to > disable kprobe attach on sys_* while it's still in kallsyms?
Was it disabled? What I noticed whas that the sys_epoll_wait wasn't present in the DWARF info present in the vmlinux file, which would be good for others to confirm, which I'll check on other machines here at home, tomorrow.
- Arnaldo
> > > > You can now use it in all perf tools, such as: > > > > perf record -e probe:SyS_epoll_wait_2 -aR sleep 1 > > > > [root@jouet ~]# > > > > So I am changing the BPF perf test to use the CamelCase notation alias: > > > > Failing (with sys_epoll_wait): > > > > [root@jouet ~]# perf test BPF > > 37: Test BPF filter : > > 37.1: Test basic BPF filtering : FAILED! > > 37.2: Test BPF prologue generation : Skip > > 37.3: Test BPF relocation checker : Skip > > [root@jouet ~]# > > > > Changing to (SyS_epoll_wait): > > > > [root@jouet ~]# perf test BPF > > 37: Test BPF filter : > > 37.1: Test basic BPF filtering : Ok > > 37.2: Test BPF prologue generation : Ok > > 37.3: Test BPF relocation checker : Ok > > [root@jouet ~]# > > > > I'm adding a fix that just makes it use SyS_epoll_wait. > > > > - Arnaldo
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