Re: [PATCH 1/1] mm,swapops: Fix compile error on set_pmd_migration_entry.

[Barry Song <21cnbao@gmail.com>]

On Sat, Dec 27, 2025 at 12:46 AM wale zhang <wale.zhang.ftd@gmail.com> wrote:
>
> On Thu, Dec 25, 2025 at 6:22 PM Barry Song <21cnbao@gmail.com> wrote:
> >
> > On Thu, Dec 25, 2025 at 10:41 PM Wale Zhang <wale.zhang.ftd@gmail.com> wrote:
> > >
> > > ../include/linux/swapops.h: In function ‘set_pmd_migration_entry’:
> > > ../include/linux/swapops.h:346:1: error: no return statement in function returning non-void [-Werror=return-type]
> > >   346 | }
> > >       | ^
> > > cc1: some warnings being treated as errors
> > >
> > > Signed-off-by: Wale Zhang <wale.zhang.ftd@gmail.com>
> >
> > Sorry. NAK.
> >
> > This looks odd. We already have a BUILD_BUG(), so no fix is needed.
> >
> > we should already have:
> > ././include/linux/compiler_types.h:631:45: error: call to
> > ‘__compiletime_assert_907’ declared with attribute error: BUILD_BUG
> > failed
> >   631 |         _compiletime_assert(condition, msg,
> > __compiletime_assert_, __COUNTER__)
> >       |                                             ^
> > ././include/linux/compiler_types.h:612:25: note: in definition of
> > macro ‘__compiletime_assert’
> >   612 |                         prefix ## suffix();
> >          \
> >       |                         ^~~~~~
> >
> > Do you actually see this being built? If so, please help identify why it
> > gets built.
>
> Hello Barry,
>
> I compile the 6.19-rc2 for arm64 with -O0, this kind of error log will appear.
> In file included from /home/wale/repo/linux/master/include/linux/leafops.h:11,
>                  from
> /home/wale/repo/linux/master/include/linux/userfaultfd_k.h:19,
>                  from /home/wale/repo/linux/master/include/linux/mm_inline.h:10,
>                  from /home/wale/repo/linux/master/mm/internal.h:13,
>                  from /home/wale/repo/linux/master/mm/fadvise.c:24:
> /home/wale/repo/linux/master/include/linux/swapops.h: In function
> ‘set_pmd_migration_entry’:
> /home/wale/repo/linux/master/include/linux/swapops.h:346:1: error: no
> return statement in function returning non-void [-Werror=return-type]
>   346 | }
>       | ^
> cc1: some warnings being treated as errors
> make[4]: *** [/home/wale/repo/linux/master/scripts/Makefile.build:287:
> mm/fadvise.o] Error 1
> make[4]: *** Waiting for unfinished jobs....
>
> There is an example on my
> github(https://github.com/wale-ftd/linux/commits/linux-6.12/) that
> used -O0 to compile the 6.12 kernel. If you're interested, you can
> check them out.

This is not my question. The BUILD_BUG here means this code
should never be built. If it is built, then that indicates a bug.
So my question is: under what kernel configuration would this
code actually get built?

Thanks
Barry