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This test places a kprobe to function getname_flags() in the kernel
which has the following prototype:

  struct filename *getname_flags(const char __user *filename, int flags, int *empty)

The 'filename' argument points to a filename located in user space memory.

Looking at commit 88903c46 ("tracing/probe: Add ustring type for
user-space string") the kprobe should indicate that user space memory is
accessed.

Output before:

   [root@m35lp76 perf]# ./perf test 66 67
   66: Use vfs_getname probe to get syscall args filenames   : FAILED!
   67: Check open filename arg using perf trace + vfs_getname: FAILED!
   [root@m35lp76 perf]#

Output after:

   [root@m35lp76 perf]# ./perf test 66 67
   66: Use vfs_getname probe to get syscall args filenames   : Ok
   67: Check open filename arg using perf trace + vfs_getname: Ok
   [root@m35lp76 perf]#

Comments from Masami Hiramatsu:

This bug doesn't happen on x86 or other archs on which user address
space...