[PATCH] tracing/hist: make err_text array fully const

[PATCH] tracing/hist: make err_text array fully const

[Huiwen He]

The err_text array contains string literals that are never modified.
Previously it was declared as:

    static const char *err_text[]

which makes the strings themselves const but allows the pointers
in the array to be changed.

Change it to:

    static const char * const err_text[]

This prevents accidental modification of the array pointers,
fixes checkpatch warnings, and allows the compiler to place the
entire array in the read-only data section (.rodata).

Signed-off-by: Huiwen He <hehuiwen@kylinos.cn>
---
 kernel/trace/trace_events_hist.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/trace/trace_events_hist.c b/kernel/trace/trace_events_hist.c
index 1d536219b624..3be35ebdaa62 100644
--- a/kernel/trace/trace_events_hist.c
+++ b/kernel/trace/trace_events_hist.c
@@ -80,7 +80,7 @@ enum { ERRORS };
 #undef C
 #define C(a, b)		b
 
-static const char *err_text[] = { ERRORS };
+static const char * const err_text[] = { ERRORS };
 
 struct hist_field;
 
-- 
2.25.1

Re: [PATCH] tracing/hist: make err_text array fully const

[kernel test robot]

Hi Huiwen,

kernel test robot noticed the following build warnings:

[auto build test WARNING on trace/for-next]
[also build test WARNING on linus/master v6.18-rc4 next-20251104]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Huiwen-He/tracing-hist-make-err_text-array-fully-const/20251104-125932
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/20251104045558.1644671-1-hehuiwen%40kylinos.cn
patch subject: [PATCH] tracing/hist: make err_text array fully const
config: riscv-randconfig-001-20251105 (https://download.01.org/0day-ci/archive/20251105/202511051436.6ZUGn3Af-lkp@intel.com/config)
compiler: riscv32-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251105/202511051436.6ZUGn3Af-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511051436.6ZUGn3Af-lkp@intel.com/

All warnings (new ones prefixed by >>):

   kernel/trace/trace_events_hist.c: In function 'hist_err':
>> kernel/trace/trace_events_hist.c:808:46: warning: passing argument 4 of 'tracing_log_err' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
     tracing_log_err(tr, last_cmd_loc, last_cmd, err_text,
                                                 ^~~~~~~~
   In file included from kernel/trace/trace_dynevent.h:14,
                    from kernel/trace/trace_synth.h:5,
                    from kernel/trace/trace_events_hist.c:22:
   kernel/trace/trace.h:2113:21: note: expected 'const char **' but argument is of type 'const char * const*'
           const char **errs, u8 type, u16 pos);
           ~~~~~~~~~~~~~^~~~


vim +808 kernel/trace/trace_events_hist.c

4b147936fa50965 Tom Zanussi      2018-01-15  802  
edfeed318d59ff2 Tom Zanussi      2022-01-28  803  static void hist_err(struct trace_array *tr, u8 err_type, u16 err_pos)
7bbab38d07f3185 Masami Hiramatsu 2018-11-05  804  {
edfeed318d59ff2 Tom Zanussi      2022-01-28  805  	if (!last_cmd)
edfeed318d59ff2 Tom Zanussi      2022-01-28  806  		return;
edfeed318d59ff2 Tom Zanussi      2022-01-28  807  
726721a51838e39 Tom Zanussi      2020-05-28 @808  	tracing_log_err(tr, last_cmd_loc, last_cmd, err_text,
726721a51838e39 Tom Zanussi      2020-05-28  809  			err_type, err_pos);
7bbab38d07f3185 Masami Hiramatsu 2018-11-05  810  }
7bbab38d07f3185 Masami Hiramatsu 2018-11-05  811  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] tracing/hist: make err_text array fully const

[kernel test robot]

Hi Huiwen,

kernel test robot noticed the following build warnings:

[auto build test WARNING on trace/for-next]
[also build test WARNING on linus/master v6.18-rc4 next-20251105]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Huiwen-He/tracing-hist-make-err_text-array-fully-const/20251104-125932
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/20251104045558.1644671-1-hehuiwen%40kylinos.cn
patch subject: [PATCH] tracing/hist: make err_text array fully const
config: sh-randconfig-r121-20251105 (https://download.01.org/0day-ci/archive/20251105/202511051755.CU1HPYCx-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 15.1.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251105/202511051755.CU1HPYCx-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511051755.CU1HPYCx-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> kernel/trace/trace_events_hist.c:808:53: sparse: sparse: incorrect type in argument 4 (different modifiers) @@     expected char const **errs @@     got char const *const * @@
   kernel/trace/trace_events_hist.c:808:53: sparse:     expected char const **errs
   kernel/trace/trace_events_hist.c:808:53: sparse:     got char const *const *

vim +808 kernel/trace/trace_events_hist.c

4b147936fa5096 Tom Zanussi      2018-01-15  802  
edfeed318d59ff Tom Zanussi      2022-01-28  803  static void hist_err(struct trace_array *tr, u8 err_type, u16 err_pos)
7bbab38d07f318 Masami Hiramatsu 2018-11-05  804  {
edfeed318d59ff Tom Zanussi      2022-01-28  805  	if (!last_cmd)
edfeed318d59ff Tom Zanussi      2022-01-28  806  		return;
edfeed318d59ff Tom Zanussi      2022-01-28  807  
726721a51838e3 Tom Zanussi      2020-05-28 @808  	tracing_log_err(tr, last_cmd_loc, last_cmd, err_text,
726721a51838e3 Tom Zanussi      2020-05-28  809  			err_type, err_pos);
7bbab38d07f318 Masami Hiramatsu 2018-11-05  810  }
7bbab38d07f318 Masami Hiramatsu 2018-11-05  811  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] tracing/hist: make err_text array fully const

[Huiwen He]

Hi Steven and Masami,

Sorry, I didn’t notice this warning when building the kernel locally.
Please ignore this patch. After further analysis, I found that unless the
prototype of tracing_log_err() is modified, this patch has no effect. It
might not be worth doing this, since the tracing_log_err() interface is
already used in multiple files in the trace subsystem.

Best regards,
Huiwen He

Re: [PATCH] tracing/hist: make err_text array fully const

[kernel test robot]

Hi Huiwen,

kernel test robot noticed the following build errors:

[auto build test ERROR on trace/for-next]
[also build test ERROR on linus/master v6.18-rc4 next-20251105]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Huiwen-He/tracing-hist-make-err_text-array-fully-const/20251104-125932
base:   https://git.kernel.org/pub/scm/linux/kernel/git/trace/linux-trace for-next
patch link:    https://lore.kernel.org/r/20251104045558.1644671-1-hehuiwen%40kylinos.cn
patch subject: [PATCH] tracing/hist: make err_text array fully const
config: x86_64-kexec (https://download.01.org/0day-ci/archive/20251105/202511052258.kdB9B0rI-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251105/202511052258.kdB9B0rI-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202511052258.kdB9B0rI-lkp@intel.com/

All errors (new ones prefixed by >>):

>> kernel/trace/trace_events_hist.c:808:46: error: passing 'const char *const[49]' to parameter of type 'const char **' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
     808 |         tracing_log_err(tr, last_cmd_loc, last_cmd, err_text,
         |                                                     ^~~~~~~~
   kernel/trace/trace.h:2113:21: note: passing argument to parameter 'errs' here
    2113 |                             const char **errs, u8 type, u16 pos);
         |                                          ^
   1 error generated.


vim +808 kernel/trace/trace_events_hist.c

4b147936fa5096 Tom Zanussi      2018-01-15  802  
edfeed318d59ff Tom Zanussi      2022-01-28  803  static void hist_err(struct trace_array *tr, u8 err_type, u16 err_pos)
7bbab38d07f318 Masami Hiramatsu 2018-11-05  804  {
edfeed318d59ff Tom Zanussi      2022-01-28  805  	if (!last_cmd)
edfeed318d59ff Tom Zanussi      2022-01-28  806  		return;
edfeed318d59ff Tom Zanussi      2022-01-28  807  
726721a51838e3 Tom Zanussi      2020-05-28 @808  	tracing_log_err(tr, last_cmd_loc, last_cmd, err_text,
726721a51838e3 Tom Zanussi      2020-05-28  809  			err_type, err_pos);
7bbab38d07f318 Masami Hiramatsu 2018-11-05  810  }
7bbab38d07f318 Masami Hiramatsu 2018-11-05  811  

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki