linux-kernel - Re: [hnaz-mm:master 272/379] lib/vsprintf.c:991:13: warning: variable 'modbuildid' set but not used

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Message-Id: <20220301102448.ff9bf910213d705842a2dd45@linux-foundation.org>
Date:   Tue, 1 Mar 2022 10:24:48 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     kernel test robot <lkp@...el.com>
Cc:     Maninder Singh <maninder1.s@...sung.com>, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org, Johannes Weiner <hannes@...xchg.org>,
        Vaneet Narang <v.narang@...sung.com>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Petr Mladek <pmladek@...e.com>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        John Ogness <john.ogness@...utronix.de>
Subject: Re: [hnaz-mm:master 272/379] lib/vsprintf.c:991:13: warning:
 variable 'modbuildid' set but not used

On Tue, 1 Mar 2022 20:11:04 +0800 kernel test robot <lkp@...el.com> wrote:

> tree:   https://github.com/hnaz/linux-mm master
> head:   a46912c14343fd3269cc133494988af90b377d9f
> commit: b314f622e664eb263ea03ef7f4580e37146f123f [272/379] kallsyms: enhance %pS/s/b printing when KALLSYSMS is disabled
> config: arm-eseries_pxa_defconfig (https://download.01.org/0day-ci/archive/20220301/202203012040.uFWGm3My-lkp@intel.com/config)
> compiler: arm-linux-gnueabi-gcc (GCC) 11.2.0
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://github.com/hnaz/linux-mm/commit/b314f622e664eb263ea03ef7f4580e37146f123f
>         git remote add hnaz-mm https://github.com/hnaz/linux-mm
>         git fetch --no-tags hnaz-mm master
>         git checkout b314f622e664eb263ea03ef7f4580e37146f123f
>         # save the config file to linux build tree
>         mkdir build_dir
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-11.2.0 make.cross O=build_dir ARCH=arm SHELL=/bin/bash
> 
> If you fix the issue, kindly add following tag as appropriate
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):
> 
>    lib/vsprintf.c: In function 'sprint_module_info':
> >> lib/vsprintf.c:991:13: warning: variable 'modbuildid' set but not used [-Wunused-but-set-variable]
>      991 |         int modbuildid = 0;
>          |             ^~~~~~~~~~

Do we care about this?  [-Wunused-but-set-variable isn't normally set. 
Under what circumstances does it get set in your setup?

I did this:

--- a/lib/vsprintf.c~kallsyms-enhance-%ps-s-b-printing-when-kallsysms-is-disabled-fix
+++ a/lib/vsprintf.c
@@ -988,7 +988,7 @@ static int sprint_module_info(char *buf,
 	unsigned long base;
 	int ret = 0;
 	const char *modname;
-	int modbuildid = 0;
+	int modbuildid __maybe_unused = 0;
 	int len;
 #if IS_ENABLED(CONFIG_STACKTRACE_BUILD_ID)
 	const unsigned char *buildid = NULL;
_


>    lib/vsprintf.c: In function 'va_format':
>    lib/vsprintf.c:1759:9: warning: function 'va_format' might be a candidate for 'gnu_printf' format attribute [-Wsuggest-attribute=format]
>     1759 |         buf += vsnprintf(buf, end > buf ? end - buf : 0, va_fmt->fmt, va);
>          |         ^~~

I wonder what this means.