linux-kernel - Re: [BUG] tracing: dynamic ftrace selftest detected failures

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Message-ID: <20240820112038.7a32b328@gandalf.local.home>
Date: Tue, 20 Aug 2024 11:20:38 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Sami Tolvanen <samitolvanen@...gle.com>
Cc: Mark Rutland <mark.rutland@....com>, Masami Hiramatsu
 <mhiramat@...nel.org>, Linux Trace Kernel
 <linux-trace-kernel@...r.kernel.org>, linux-kernel@...r.kernel.org,
 clang-built-linux <llvm@...ts.linux.dev>, Nathan Chancellor
 <nathan@...nel.org>
Subject: Re: [BUG] tracing: dynamic ftrace selftest detected failures

On Tue, 20 Aug 2024 08:10:42 -0700
Sami Tolvanen <samitolvanen@...gle.com> wrote:

> On Tue, Aug 20, 2024 at 3:48 AM Mark Rutland <mark.rutland@....com> wrote:
> >
> > On Tue, Aug 20, 2024 at 10:03:30AM +0900, Masami Hiramatsu wrote:  
> > > On Mon, 19 Aug 2024 12:02:44 -0400
> > > Steven Rostedt <rostedt@...dmis.org> wrote:
> > >  
> > > > On Tue, 20 Aug 2024 00:56:49 +0900
> > > > Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:  
> > > > >  
> > > > > >
> > > > > > We may need to add "noinline" or something to make sure those functions
> > > > > > don't get inlined for LTO.  
> > > > >
> > > > > Yeah, we need such option at least for function call test.  
> > > >
> > > > Could you add the noinline, and if it fixes the issue send a patch?  
> > >
> > > I found the target function already has "noinline". I tried to add noinline
> > > to the testing function (callsite), but it also did not work.
> > > I think "noinline" is for the compiler, but LTO is done by the linker.  
> >
> > If LTO is breaking noinline, then that has much larger implications for
> > noinstr code and similar, and means that LTO is unsound...  
> 
> The noinline attribute is preserved in LLVM IR, so it should continue
> to work with LTO. Which function are we talking about here? Are you
> sure the function was inlined instead of being dropped completely?
> Does marking the function __used help?

Hmm, maybe it was dropped, as the functions are basically just stubs.

Masami, can you add __used to the functions in trace_selftests_dynamic.c
and see if that fixes it?

-- Steve