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

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Message-Id: <20240821091503.097e729cecb8560f8f51a646@kernel.org>
Date: Wed, 21 Aug 2024 09:15:03 +0900
From: Masami Hiramatsu (Google) <mhiramat@...nel.org>
To: Steven Rostedt <rostedt@...dmis.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 Tue, 20 Aug 2024 19:49:14 -0400
Steven Rostedt <rostedt@...dmis.org> wrote:

> On Wed, 21 Aug 2024 08:43:51 +0900
> Masami Hiramatsu (Google) <mhiramat@...nel.org> wrote:
> 
> > > Can you add the __used and see if it fixes it?  
> > 
> > Adding __used to DYN_FTRACE_TEST_NAME() and DYN_FTRACE_TEST_NAME2() does
> > not change, the test still fails.
> 
> OK, now that sounds like a bug in LTO itself.

Hmm, I think __used just preserve the function exists as a function. But the
callsite can be optimized. This mean the __used function code is duplicated,
and embedded one copy in the callsite, but keep another copy as a function
which can be used from outside. But "noinline" attribute seems to be expected
not embedded in the callsite (because that is what "inlined" mean), so it
looks like a bug.

Thank you,

> 
> -- Steve


-- 
Masami Hiramatsu (Google) <mhiramat@...nel.org>