Re: [PATCH v2] ftrace: Hide a extra entry in stack trace

[Tatsuya S]

On 10/1/24 10:47 PM, Steven Rostedt wrote:
> On Tue, 1 Oct 2024 22:27:03 +0900
> ts <tatsuya.s2862@xxxxxxxxx> wrote:
>
> > > ...
> > >                 sh-140     [001] ...1.    18.352601: myevent: (vfs_write+0x4/0x560)
> > >                 sh-140     [001] ...1.    18.352602: <stack trace>
> > >    => ksys_write
> > >    => do_syscall_64
> > >    => entry_SYSCALL_64_after_hwframe
> > >                 sh-140     [001] ...1.    18.352602: vfs_write <-ksys_write
> > >                 sh-140     [001] ...1.    18.352604: <stack trace>
> > >    => ftrace_regs_call
> > >    => vfs_write
> > >    => ksys_write
> > >    => do_syscall_64
> > >    => entry_SYSCALL_64_after_hwframe
> > > ------
> > > As you can see, myevent skips "vfs_write".
> > > (and function tracer still have ftrace_regs_call() )
> >
> > Thanks for the other tests. This issue may be function_trace_call()
> > specific problem.
> >
> > So I will change the place to increment skip number.
>
> My fear is that we are going to just break it elsewhere. The problem with
> the "skip" is that there's so many configurations when we get here, we may
> not really know what to skip. If the compiler inlines something, then we
> may skip something we do not want to.
>
> I rather have extra information than not enough.
>
> -- Steve

It may not be clean and be bit redundant, but I think it would be more 
maintainable to treat

"skip(and skipped functions)" separately only at the top(parent) of 
functions that display stack trace.


thanks.