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Date:   Thu, 24 Feb 2022 11:01:30 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        joao@overdrivepizza.com, hjl.tools@gmail.com, jpoimboe@redhat.com,
        andrew.cooper3@citrix.com, linux-kernel@vger.kernel.org,
        ndesaulniers@google.com, keescook@chromium.org,
        samitolvanen@google.com, mark.rutland@arm.com,
        alyssa.milburn@intel.com, mbenes@suse.cz,
        alexei.starovoitov@gmail.com
Subject: Re: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry__ location
Message-ID: <20220224110130.4f4ae4ac@gandalf.local.home>
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        <20220224151322.714815604@infradead.org>
        <20220225005520.c69be2fbdbd28028361792d9@kernel.org>
        <20220224105847.5c899324@gandalf.local.home>
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On Thu, 24 Feb 2022 10:58:47 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> On Fri, 25 Feb 2022 00:55:20 +0900
> Masami Hiramatsu <mhiramat@kernel.org> wrote:
> 
> > >  unsigned long ftrace_location(unsigned long ip)
> > >  {
> > > -	return ftrace_location_range(ip, ip);
> > > +	struct dyn_ftrace *rec;
> > > +	unsigned long offset;
> > > +	unsigned long size;
> > > +
> > > +	rec = lookup_rec(ip, ip);
> > > +	if (!rec) {
> > > +		if (!kallsyms_lookup_size_offset(ip, &size, &offset))
> > > +			goto out;
> > > +
> > > +		if (!offset)    
> > 
> > Isn't this 'if (offset)' ?  
> 
> No, the point to only look for the fentry location if the ip passed in
> points to the start of the function. IOW, +0 offset.
> 

I do agree with Masami that it is confusing. Please add a comment:

		/* Search the entire function if ip is the start of the function */
		if (!offset)
			[..]

-- Steve

> 
> 
> >   
> > > +			rec = lookup_rec(ip - offset, (ip - offset) + size);
> > > +	}
> > > +
> > > +	if (rec)
> > > +		return rec->ip;
> > > +
> > > +out:
> > > +	return 0;