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_ 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? > > 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
