linux-kernel - Re: [PATCH] mm: vmstat.h: Annotate operations between enums

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Message-ID: <CANiDSCt_RALHi4O313bzi=Grr=sCV+Y8WmHmOF8JpttHw6nFpA@mail.gmail.com>
Date: Mon, 2 Dec 2024 18:27:48 +0100
From: Ricardo Ribalda <ribalda@...omium.org>
To: Nathan Chancellor <nathan@...nel.org>
Cc: Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] mm: vmstat.h: Annotate operations between enums

On Mon, 2 Dec 2024 at 17:18, Nathan Chancellor <nathan@...nel.org> wrote:
>
> Hi Ricardo,
>
> On Mon, Dec 02, 2024 at 04:02:19PM +0000, Ricardo Ribalda wrote:
> > Compiler is confused when we do arithmetic operations between two
> > different enum types.
> > In this case NR_VM_STAT_ITEMS and NR_LRU_BASE are not actual
> > enumerators, they are used to find the first and the count of the
> > enumerator.
> >
> > Add a casting to int, to avoid the following llvm 9 warning:
> > ./include/linux/vmstat.h:504:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
> >   504 |         return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
> >       |                            ~~~~~~~~~~~~~~~~~~~~~ ^
> >   505 |                            item];
> >       |                            ~~~~
> > ./include/linux/vmstat.h:511:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
> >   511 |         return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
> >       |                            ~~~~~~~~~~~~~~~~~~~~~ ^
> >   512 |                            NR_VM_NUMA_EVENT_ITEMS +
> >       |                            ~~~~~~~~~~~~~~~~~~~~~~
> > ./include/linux/vmstat.h:518:36: warning: arithmetic between different enumeration types ('enum node_stat_item' and 'enum lru_list') [-Wenum-enum-conversion]
> >   518 |         return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
> >       |                               ~~~~~~~~~~~ ^ ~~~
> > ./include/linux/vmstat.h:524:43: warning: arithmetic between different enumeration types ('enum zone_stat_item' and 'enum numa_stat_item') [-Wenum-enum-conversion]
> >   524 |         return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
> >       |                            ~~~~~~~~~~~~~~~~~~~~~ ^
> >   525 |                            NR_VM_NUMA_EVENT_ITEMS +
> >       |                            ~~~~~~~~~~~~~~~~~~~~~~
> >
> > Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
>
> I think it is just better to disable this specific warning for normal
> and W=1 builds so that it is not visible for people, as this objectively
> makes the code uglier:
>
> https://lore.kernel.org/20241008005136.GA241099@thelio-3990X/
>
> https://lore.kernel.org/20241017-disable-two-clang-enum-warnings-v2-1-163ac04346ae@kernel.org/

Thanks for the heads-up.

Either disabling the config or this patch will work for my usecase (media-ci).

FWIW, we only need 3 patches (plus this) to build media with W=1 and llvm19....

I do not think that this patch is very ugly :P

>
> I have just pinged that patch for acceptance.
>
> Cheers,
> Nathan
>
> > ---
> >  include/linux/vmstat.h | 9 ++++-----
> >  1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
> > index d2761bf8ff32..32c641d25bea 100644
> > --- a/include/linux/vmstat.h
> > +++ b/include/linux/vmstat.h
> > @@ -501,27 +501,26 @@ static inline const char *zone_stat_name(enum zone_stat_item item)
> >  #ifdef CONFIG_NUMA
> >  static inline const char *numa_stat_name(enum numa_stat_item item)
> >  {
> > -     return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
> > -                        item];
> > +     return vmstat_text[(int)NR_VM_ZONE_STAT_ITEMS + item];
> >  }
> >  #endif /* CONFIG_NUMA */
> >
> >  static inline const char *node_stat_name(enum node_stat_item item)
> >  {
> > -     return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
> > +     return vmstat_text[(int)NR_VM_ZONE_STAT_ITEMS +
> >                          NR_VM_NUMA_EVENT_ITEMS +
> >                          item];
> >  }
> >
> >  static inline const char *lru_list_name(enum lru_list lru)
> >  {
> > -     return node_stat_name(NR_LRU_BASE + lru) + 3; // skip "nr_"
> > +     return node_stat_name((int)NR_LRU_BASE + lru) + 3; // skip "nr_"
> >  }
> >
> >  #if defined(CONFIG_VM_EVENT_COUNTERS) || defined(CONFIG_MEMCG)
> >  static inline const char *vm_event_name(enum vm_event_item item)
> >  {
> > -     return vmstat_text[NR_VM_ZONE_STAT_ITEMS +
> > +     return vmstat_text[(int)NR_VM_ZONE_STAT_ITEMS +
> >                          NR_VM_NUMA_EVENT_ITEMS +
> >                          NR_VM_NODE_STAT_ITEMS +
> >                          NR_VM_STAT_ITEMS +
> >
> > ---
> > base-commit: 40384c840ea1944d7c5a392e8975ed088ecf0b37
> > change-id: 20241202-fix-vmstat-88968bcaa955
> >
> > Best regards,
> > --
> > Ricardo Ribalda <ribalda@...omium.org>
> >



-- 
Ricardo Ribalda