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. 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? -- Steve
