Re: [PATCH v2 4/5] perf kvm: Support sampling guest callchains

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

Hi Tianyi,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 8a749fd1a8720d4619c91c8b6e7528c0a355c0aa]

url:    https://github.com/intel-lab-lkp/linux/commits/Tianyi-Liu/KVM-Add-arch-specific-interfaces-for-sampling-guest-callchains/20231008-230042
base:   8a749fd1a8720d4619c91c8b6e7528c0a355c0aa
patch link:    https://lore.kernel.org/r/SY4P282MB108433024762F1F292D47C2A9DCFA%40SY4P282MB1084.AUSP282.PROD.OUTLOOK.COM
patch subject: [PATCH v2 4/5] perf kvm: Support sampling guest callchains
config: i386-tinyconfig (https://download.01.org/0day-ci/archive/20231009/202310090338.4PmYjmBS-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20231009/202310090338.4PmYjmBS-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/202310090338.4PmYjmBS-lkp@intel.com/

All warnings (new ones prefixed by >>):

   arch/x86/events/core.c: In function 'perf_callchain_guest32':
>> arch/x86/events/core.c:2784:43: warning: passing argument 1 of 'perf_guest_read_virt' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
    2784 |                 if (!perf_guest_read_virt(&fp->next_frame, &frame.next_frame,
         |                                           ^~~~~~~~~~~~~~~
   In file included from arch/x86/events/core.c:15:
   include/linux/perf_event.h:1531:41: note: expected 'void *' but argument is of type 'const u32 *' {aka 'const unsigned int *'}
    1531 | static inline bool perf_guest_read_virt(void*, void*, unsigned int)     { return 0; }
         |                                         ^~~~~
   arch/x86/events/core.c:2787:43: warning: passing argument 1 of 'perf_guest_read_virt' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
    2787 |                 if (!perf_guest_read_virt(&fp->return_address, &frame.return_address,
         |                                           ^~~~~~~~~~~~~~~~~~~
   include/linux/perf_event.h:1531:41: note: expected 'void *' but argument is of type 'const u32 *' {aka 'const unsigned int *'}
    1531 | static inline bool perf_guest_read_virt(void*, void*, unsigned int)     { return 0; }
         |                                         ^~~~~
   arch/x86/events/core.c: In function 'perf_callchain_guest':
   arch/x86/events/core.c:2808:51: warning: passing argument 1 of 'perf_guest_read_virt' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
    2808 |                         if (!perf_guest_read_virt(&fp->next_frame, &frame.next_frame,
         |                                                   ^~~~~~~~~~~~~~~
   include/linux/perf_event.h:1531:41: note: expected 'void *' but argument is of type 'struct stack_frame * const*'
    1531 | static inline bool perf_guest_read_virt(void*, void*, unsigned int)     { return 0; }
         |                                         ^~~~~
   arch/x86/events/core.c:2811:51: warning: passing argument 1 of 'perf_guest_read_virt' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
    2811 |                         if (!perf_guest_read_virt(&fp->return_address, &frame.return_address,
         |                                                   ^~~~~~~~~~~~~~~~~~~
   include/linux/perf_event.h:1531:41: note: expected 'void *' but argument is of type 'const long unsigned int *'
    1531 | static inline bool perf_guest_read_virt(void*, void*, unsigned int)     { return 0; }
         |                                         ^~~~~


vim +2784 arch/x86/events/core.c

  2775	
  2776	static inline void
  2777	perf_callchain_guest32(struct perf_callchain_entry_ctx *entry)
  2778	{
  2779		struct stack_frame_ia32 frame;
  2780		const struct stack_frame_ia32 *fp;
  2781	
  2782		fp = (void *)perf_guest_get_frame_pointer();
  2783		while (fp && entry->nr < entry->max_stack) {
> 2784			if (!perf_guest_read_virt(&fp->next_frame, &frame.next_frame,
  2785				sizeof(frame.next_frame)))
  2786				break;
  2787			if (!perf_guest_read_virt(&fp->return_address, &frame.return_address,
  2788				sizeof(frame.return_address)))
  2789				break;
  2790			perf_callchain_store(entry, frame.return_address);
  2791			fp = (void *)frame.next_frame;
  2792		}
  2793	}
  2794	

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