On Thu, 8 Jun 2023 16:52:34 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Wed, 17 May 2023 19:59:04 +0900 > "Masami Hiramatsu (Google)" <mhiramat@xxxxxxxxxx> wrote: > > > Add fprobe events for tracing function entry and exit instead of kprobe > > events. With this change, we can continue to trace function entry/exit > > even if the CONFIG_KPROBES_ON_FTRACE is not available. Since > > CONFIG_KPROBES_ON_FTRACE requires the CONFIG_DYNAMIC_FTRACE_WITH_REGS, > > it is not available if the architecture only supports > > CONFIG_DYNAMIC_FTRACE_WITH_ARGS. And that means kprobe events can not > > probe function entry/exit effectively on such architecture. > > But this can be solved if the dynamic events supports fprobe events. > > > > The fprobe event is a new dynamic events which is only for the function > > (symbol) entry and exit. This event accepts non register fetch arguments > > so that user can trace the function arguments and return values. > > > > The fprobe events syntax is here; > > > > f[:[GRP/][EVENT]] FUNCTION [FETCHARGS] > > f[MAXACTIVE][:[GRP/][EVENT]] FUNCTION%return [FETCHARGS] > > I finally got around to look at these (I know you already queued them), but > looking at the above, the "%return" is redundant. > > > > > E.g. > > > > # echo 'f vfs_read $arg1' >> dynamic_events > > # echo 'f vfs_read%return $retval' >> dynamic_events > > # cat dynamic_events > > f:fprobes/vfs_read__entry vfs_read arg1=$arg1 > > f:fprobes/vfs_read__exit vfs_read%return arg1=$retval > > Can't we just have: > > f:fprobes/vfs_read__entry vfs_read arg1=$arg1 > f:fprobes/vfs_read__exit vfs_read arg1=$retval > > Where if "$retval" is specified, it automatically becomes a return? If > anything else is specified, it errors out. That is, if $retval is > specified, it becomes a return probe, as a return probe can only have > $retval. If anything else is specified, it errors out if $retval is also > specified. Hmm, current implementation design doesn't allow that. It parses the 'place' and 'args' sequencially because what 'args' is available depends on the place. > > Now if it's a void function, and you just want to make it a return then we > can have your: > > f:fprobes/vfs_read__exit vfs_read%return > > Thoughts? But this sounds useful. Let me try to scan the argument to find $retval. Thank you, > > -- Steve > > > -- Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
