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f994592d93
To work like strace and dereference syscall pointer args we need to insert probes (or tracepoints) right after we copy those bytes from userspace. Since we're formatting the syscall args at raw_syscalls:sys_enter time, we need to have a formatter that just stores the position where, later, when we get the probe:vfs_getname, we can insert the pointer contents. Now, if a probe:vfs_getname with this format is in place: # perf probe -l probe:vfs_getname (on getname_flags:72@/home/git/linux/fs/namei.c with pathname) That was, in this case, put in place with: # perf probe 'vfs_getname=getname_flags:72 pathname=filename:string' Added new event: probe:vfs_getname (on getname_flags:72 with pathname=filename:string) You can now use it in all perf tools, such as: perf record -e probe:vfs_getname -aR sleep 1 # Then 'perf trace' will notice that and do the pointer -> contents expansion: # trace -e open touch /tmp/bla 0.165 (0.010 ms): touch/17752 open(filename: /etc/ld.so.cache, flags: CLOEXEC) = 3 0.195 (0.011 ms): touch/17752 open(filename: /lib64/libc.so.6, flags: CLOEXEC) = 3 0.512 (0.012 ms): touch/17752 open(filename: /usr/lib/locale/locale-archive, flags: CLOEXEC) = 3 0.582 (0.012 ms): touch/17752 open(filename: /tmp/bla, flags: CREAT|NOCTTY|NONBLOCK|WRONLY, mode: 438) = 3 # Roughly equivalent to strace's output: # strace -rT -e open touch /tmp/bla 0.000000 open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3 <0.000039> 0.000317 open("/lib64/libc.so.6", O_RDONLY|O_CLOEXEC) = 3 <0.000102> 0.001461 open("/usr/lib/locale/locale-archive", O_RDONLY|O_CLOEXEC) = 3 <0.000072> 0.000405 open("/tmp/bla", O_WRONLY|O_CREAT|O_NOCTTY|O_NONBLOCK, 0666) = 3 <0.000055> 0.000641 +++ exited with 0 +++ # Now we need to either look for at all syscalls that are marked as pointers and have some well known names ("filename", "pathname", etc) and set the arg formatter to the one used for the "open" syscall in this patch. This implementation works for syscalls with just a string being copied from userspace, for matching syscalls with more than one string being copied via the same probe/trace point (vfs_getname) we need to extend the vfs_getname probe spec to include the pointer too, but there are some problems with that in 'perf probe' or the kernel kprobes code, need to investigate before considering supporting multiple strings per syscall. Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Borislav Petkov <bp@suse.de> Cc: David Ahern <dsahern@gmail.com> Cc: Frederic Weisbecker <fweisbec@gmail.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Milian Wolff <mail@milianw.de> Cc: Namhyung Kim <namhyung@kernel.org> Cc: Stephane Eranian <eranian@google.com> Link: http://lkml.kernel.org/n/tip-xvuwx6nuj8cf389kf9s2ue2s@git.kernel.org Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com> |
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