linux-kernel - Re: [PATCH v1 1/1] panic: Fix compilation error (`make W=1`)

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Message-ID: <aHB7fV7QgNp8Fre4@U-2FWC9VHC-2323.local>
Date: Fri, 11 Jul 2025 10:48:29 +0800
From: Feng Tang <feng.tang@...ux.alibaba.com>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
	linux-kernel@...r.kernel.org,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Petr Mladek <pmladek@...e.com>
Subject: Re: [PATCH v1 1/1] panic: Fix compilation error (`make W=1`)

On Thu, Jul 10, 2025 at 06:49:47PM -0700, Nathan Chancellor wrote:
> On Fri, Jul 11, 2025 at 08:54:25AM +0800, Feng Tang wrote:
> > On Thu, Jul 10, 2025 at 03:01:33PM -0700, Andrew Morton wrote:
> > > On Thu, 10 Jul 2025 12:48:16 +0300 Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> > > 
> > > > Compiler is not happy about the recently added code:
> > > > 
> > > > lib/sys_info.c:52:19: error: variable 'sys_info_avail' is not needed and will not be emitted [-Werror,-Wunneeded-internal-declaration]
> > > >    52 | static const char sys_info_avail[] = "tasks,mem,timers,locks,ftrace,all_bt,blocked_tasks";
> > > >       |                   ^~~~~~~~~~~~~~
> > > > 
> > > > Fix it in the same way how, for example, lib/vsprintf.c does in the similar
> > > > cases, i.e. by using string literal directly as sizeof() parameter.
> > > > 
> > > > ...
> > > >
> > > 
> > > > --- a/lib/sys_info.c
> > > > +++ b/lib/sys_info.c
> > > > @@ -49,13 +49,11 @@ unsigned long sys_info_parse_param(char *str)
> > > >  
> > > >  #ifdef CONFIG_SYSCTL
> > > >  
> > > > -static const char sys_info_avail[] = "tasks,mem,timers,locks,ftrace,all_bt,blocked_tasks";
> > > > -
> > > >  int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
> > > >  					  void *buffer, size_t *lenp,
> > > >  					  loff_t *ppos)
> > > >  {
> > > > -	char names[sizeof(sys_info_avail) + 1];
> > > > +	char names[sizeof("tasks,mem,timers,locks,ftrace,all_bt,blocked_tasks") + 1];
> > > >  	struct ctl_table table;
> > > >  	unsigned long *si_bits_global;
> > > >  
> > > 
> > > Yes, that's neater than the fix we currently have.  I'll grab, thanks.
> > 
> > Hi Andrew, Andy,
> > 
> > sys_info_avail[] has another purpose for being a counterpart of si_names[],
> > which could be extended in future, so we make it obviously stand-alone. As
> > for definition of si_names[], we explicitly added comment:  
> > 
> > 	/*
> > 	 * When 'si_names' gets updated,  please make sure the 'sys_info_avail'
> > 	 * below is updated accordingly.
> > 	 */
> > 	static const struct sys_info_name  si_names[] = {
> > 		{ SYS_INFO_TASKS,		"tasks" },
> > 		{ SYS_INFO_MEM,			"mem" },
> > 		
> > which has also been discussed in another thread:
> > https://lore.kernel.org/lkml/aG3o2RFHc5iXnJef@U-2FWC9VHC-2323.local/
> > 
> > And I suggest to keep sys_info_avail[], and either Nathan or Sergey's patch
> > works for me.
> 
> We could do something like this to keep the sizeof() obvious and
> separate, while still eliminating the variable? Happy to bike shed
> aspects of it like the macro name and such.
> 
> diff --git a/lib/sys_info.c b/lib/sys_info.c
> index 46d6f4f1ad2a..c1df502a2c0d 100644
> --- a/lib/sys_info.c
> +++ b/lib/sys_info.c
> @@ -14,7 +14,7 @@ struct sys_info_name {
>  };
>  
>  /*
> - * When 'si_names' gets updated,  please make sure the 'sys_info_avail'
> + * When 'si_names' gets updated,  please make sure SYS_INFO_MAX_LEN
>   * below is updated accordingly.
>   */
>  static const struct sys_info_name  si_names[] = {
> @@ -49,13 +49,13 @@ unsigned long sys_info_parse_param(char *str)
>  
>  #ifdef CONFIG_SYSCTL
>  
> -static const char sys_info_avail[] = "tasks,mem,timers,locks,ftrace,all_bt,blocked_tasks";
> +#define SYS_INFO_MAX_LEN (sizeof("tasks,mem,timers,locks,ftrace,all_bt,blocked_tasks") + 1)
>  
>  int sysctl_sys_info_handler(const struct ctl_table *ro_table, int write,
>  					  void *buffer, size_t *lenp,
>  					  loff_t *ppos)
>  {
> -	char names[sizeof(sys_info_avail) + 1];
> +	char names[SYS_INFO_MAX_LEN];
>  	struct ctl_table table;
>  	unsigned long *si_bits_global;
  
Looks great to me, thanks!

We can even move the SYS_INFO_MAX_LEN definition close to si_names[],
initially sys_info_avail[] was next to si_names[], and was moved inside 
"#ifdef CONFIG_SYSCTL" region for compiling CONFIG_SYSCTL=n case.

> ---
> 
> > Sorry for the inconvenience, and I should upgrade my gcc :) 
> 
> I am not sure that GCC has this warning, I have only ever seen it with
> clang.

Got it.

Thanks,
Feng