From: Nathan Chancellor <nathan@kernel.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: kernel test robot <lkp@intel.com>,
chongjiapeng <jiapeng.chong@linux.alibaba.com>,
llvm@lists.linux.dev, kbuild-all@lists.01.org,
linux-kernel@vger.kernel.org
Subject: Re: kernel/trace/ftrace.c:7157:20: error: unused function 'ftrace_startup_enable'
Date: Mon, 14 Feb 2022 08:53:04 -0700 [thread overview]
Message-ID: <Ygp64CsyyKyRykqE@dev-arch.archlinux-ax161> (raw)
In-Reply-To: <20220214102000.1d3af66e@gandalf.local.home>
Hi Steve,
On Mon, Feb 14, 2022 at 10:20:00AM -0500, Steven Rostedt wrote:
> On Sun, 13 Feb 2022 21:03:29 +0800
> kernel test robot <lkp@intel.com> wrote:
>
> > All errors (new ones prefixed by >>):
> >
> > >> kernel/trace/ftrace.c:7157:20: error: unused function 'ftrace_startup_enable' [-Werror,-Wunused-function]
> > static inline void ftrace_startup_enable(int command) { }
> > ^
> > 1 error generated.
>
> Strange. I always thought that static inline functions do not cause
> warnings when not used? Especially, since they are often in headers when
> things are turned off. Or is it because this is in a C file?
With -Wunused-function, clang will warn about unused static inline
functions within a .c file (but not .h), whereas GCC will not warn for
either. The unused attribute was added to the definition of inline to
make clang's behavior match GCC's.
> Is this a new warning caused by a commit, or is it a new warning because
> the compiler now complains about it?
However, in commit 6863f5643dd7 ("kbuild: allow Clang to find unused
static inline functions for W=1 build"), Masahiro made it so that the
unused attribute does not get added at W=1 so that instances of unused
static inline functions can be caught and eliminated (or put into use,
if the function should have been used), hence this report.
I will be honest, I don't know why the robot flagged 172f7ba9772c as the
commit that introduced this warning but it seems legitimate if
CONFIG_DYNAMIC_FTRACE is not enabled, since ftrace_startup_enable() is
only ever used within an '#ifdef CONFIG_DYNAMIC_FTRACE' block so I guess
the stub is unnecessary?
Cheers,
Nathan
next prev parent reply other threads:[~2022-02-14 15:53 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-13 13:03 kernel/trace/ftrace.c:7157:20: error: unused function 'ftrace_startup_enable' kernel test robot
2022-02-14 15:20 ` Steven Rostedt
2022-02-14 15:53 ` Nathan Chancellor [this message]
2022-02-14 16:28 ` Masahiro Yamada
2022-02-14 17:00 ` Nathan Chancellor
2022-02-14 18:57 ` Steven Rostedt
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