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Date: Tue, 15 Feb 2022 01:28:53 +0900 From: Masahiro Yamada <masahiroy@...nel.org> To: Nathan Chancellor <nathan@...nel.org> Cc: Steven Rostedt <rostedt@...dmis.org>, kernel test robot <lkp@...el.com>, chongjiapeng <jiapeng.chong@...ux.alibaba.com>, llvm@...ts.linux.dev, kbuild-all@...ts.01.org, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: kernel/trace/ftrace.c:7157:20: error: unused function 'ftrace_startup_enable' On Tue, Feb 15, 2022 at 12:53 AM Nathan Chancellor <nathan@...nel.org> wrote: > > 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@...el.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. BTW, my hope was to move this warning to W=0 someday. (that is, remove __inline_maybe_unused entirely). I do not know how many warnings are still remaining, though. Is it now more difficult due to CONFIG_WERROR? > 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 -- Best Regards Masahiro Yamada
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