linux-kernel - Re: vmlinux.o: warning: objtool: stackleak_erase()+0x35: call to ftrace_likely

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Date:   Mon, 4 Apr 2022 15:25:02 -0400
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, kernel test robot <lkp@...el.com>
Subject: Re: vmlinux.o: warning: objtool: stackleak_erase()+0x35: call to
 ftrace_likely_update() leaves .noinstr.text section

On Mon, 4 Apr 2022 11:27:47 -0700
Kees Cook <keescook@...omium.org> wrote:

> I got CCed on this because of stackleak_erase() triggering, this, but it
> appears to be an existing issue for other callers too. It looks like
> __branch_check__() shouldn't be emitting ftrace_likely_update() calls
> for noinstr functions...
> 
> I have no idea how a macro is meant to check for function attributes,
> though... :(

Ignore it. It's the branch tracer enabled (that is, every "if ()" is being
traced).

Although I still use the branch profiler, I do not believe anyone uses the
branch tracer. The branch profiler updates an array of counters that tells
when the branch was true or false, the branch tracer actually traces
(records an event) for every branch in the system!

I think I'll just send a patch to nuke the tracer. I'm sure Peter Zijlstra
will be happy when I do that. But I still want the profiler, as I find that
useful.

-- Steve