On Tue, Aug 02, 2016 at 11:15:34PM -0300, Arnaldo Carvalho de Melo wrote: > 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.
as far as I can see sys_ and SyS_ both present in kallsyms, so kprobe infra should recognize both, the question is why perf decided to ingore sys_ version?
