Re: [RFC PATCH] rseq: Validate read-only fields under DEBUG_RSEQ config

[kernel test robot <lkp@intel.com>]

Hi Mathieu,

[This is a private test report for your RFC patch.]
kernel test robot noticed the following build warnings:

[auto build test WARNING on tip/sched/core]
[also build test WARNING on akpm-mm/mm-everything linus/master v6.12-rc4 next-20241022]
[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/Mathieu-Desnoyers/rseq-Validate-read-only-fields-under-DEBUG_RSEQ-config/20241019-011655
base:   tip/sched/core
patch link:    https://lore.kernel.org/r/20241018171219.256647-1-mathieu.desnoyers%40efficios.com
patch subject: [RFC PATCH] rseq: Validate read-only fields under DEBUG_RSEQ config
config: s390-allmodconfig (https://download.01.org/0day-ci/archive/20241023/202410231007.2hFp5Cwl-lkp@intel.com/config)
compiler: clang version 20.0.0git (https://github.com/llvm/llvm-project 5886454669c3c9026f7f27eab13509dd0241f2d6)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20241023/202410231007.2hFp5Cwl-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/202410231007.2hFp5Cwl-lkp@intel.com/

All warnings (new ones prefixed by >>):

   In file included from arch/s390/purgatory/purgatory.c:10:
   In file included from include/linux/kexec.h:18:
   In file included from include/linux/vmcore_info.h:6:
   In file included from include/linux/elfcore.h:7:
   In file included from include/linux/sched/task_stack.h:9:
>> include/linux/sched.h:1368:16: warning: field 'rseq_fields' with variable sized type 'struct rseq' not at the end of a struct or class is a GNU extension [-Wgnu-variable-sized-type-not-at-end]
    1368 |         struct rseq                     rseq_fields;
         |                                         ^
   1 warning generated.


vim +1368 include/linux/sched.h

  1357	
  1358	#ifdef CONFIG_RSEQ
  1359		struct rseq __user *rseq;
  1360		u32 rseq_len;
  1361		u32 rseq_sig;
  1362		/*
  1363		 * RmW on rseq_event_mask must be performed atomically
  1364		 * with respect to preemption.
  1365		 */
  1366		unsigned long rseq_event_mask;
  1367	# ifdef CONFIG_DEBUG_RSEQ
> 1368		struct rseq			rseq_fields;
  1369	# endif
  1370	#endif
  1371	

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