linux-kernel - Re: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry_

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Date:   Wed, 09 Mar 2022 17:17:49 +0530
From:   "Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Steven Rostedt <rostedt@...dmis.org>
Cc:     alexei.starovoitov@...il.com, alyssa.milburn@...el.com,
        andrew.cooper3@...rix.com, hjl.tools@...il.com,
        joao@...rdrivepizza.com, jpoimboe@...hat.com,
        keescook@...omium.org, linux-kernel@...r.kernel.org,
        mark.rutland@....com, mbenes@...e.cz,
        Masami Hiramatsu <mhiramat@...nel.org>,
        ndesaulniers@...gle.com, samitolvanen@...gle.com, x86@...nel.org
Subject: Re: [PATCH v2 12/39] x86/ibt,ftrace: Search for __fentry__ location

Peter Zijlstra wrote:
> On Thu, Mar 03, 2022 at 09:34:13AM -0500, Steven Rostedt wrote:
>> On Thu, 3 Mar 2022 14:04:52 +0100
>> Peter Zijlstra <peterz@...radead.org> wrote:
>> 
>> > > @@ -1596,7 +1596,7 @@ static int check_ftrace_location(struct kprobe *p)
>> > > {
>> > > 	unsigned long ftrace_addr;
>> > > 
>> > > -	ftrace_addr = ftrace_location((unsigned long)p->addr);
>> > > +	ftrace_addr = ftrace_location_range((unsigned long)p->addr, (unsigned long)p->addr);  
>> > 
>> > Yes, although perhaps a new helper. I'll go ponder during lunch.
>> 
>> Is there more places to add that to make it worth creating a helper?
> 
> This is what I ended up with, I've looked at all ftrace_location() sites
> there are, seems to work too, both the built-in boot time ftrace tests
> and the selftests work splat-less.
> 
> I should update the Changelog some though.
> 
> Naveen also mentioned register_ftrace_direct() could be further cleaned
> up, but I didn't want to do too much in once go.

Not a problem, I can send those as cleanups atop this series.

> 
> ---
> 
> Subject: x86/ibt,ftrace: Search for __fentry__ location
> From: Peter Zijlstra <peterz@...radead.org>
> Date: Wed Feb 23 10:01:38 CET 2022
> 
> Have ftrace_location() search the symbol for the __fentry__ location
> when it isn't at func+0 and use this for {,un}register_ftrace_direct().
> 
> This avoids a whole bunch of assumptions about __fentry__ being at
> func+0.
> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---

This version looks good to me.
Acked-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>


Thanks,
Naveen