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

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Message-ID: <20240820181109.4203158d@gandalf.local.home>
Date: Tue, 20 Aug 2024 18:11:09 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: "Masami Hiramatsu (Google)" <mhiramat@...nel.org>
Cc: Sami Tolvanen <samitolvanen@...gle.com>, Mark Rutland
 <mark.rutland@....com>, 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 Wed, 21 Aug 2024 07:05:39 +0900
Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:


> Does the noinline attribute prevent embedding callsite too? I mean
> 
> extern callee()
> 
> noinline callee()
> {
> ...
> }
> 
> caller()
> {
> 	callee() // (*)
> }
> 
> In this case, does noinline prevent LTO to embed the callee at the callsite(*)
> or prevent LTO remove the callee() symbol?
>

Even though we have it passed as a parameter, I think the compiler and
linker is smart enough to see that and notice its use, and that the
function passed in is a nop, which doesn't break the flow.

Can you add the __used and see if it fixes it?

-- Steve