Re: [PATCH] include/c: re-add type checking in container_of()

[Ruediger Meier <sweet_f_a@gmx.de>]

On Monday 03 December 2018, Karel Zak wrote:
> On Sun, Dec 02, 2018 at 07:23:45PM +0100, Ruediger Meier wrote:
> > From: Ruediger Meier <ruediger.meier@ga-group.nl>
> >
> > This reverts parts of commit eb06d5d4, which seems to be based on
> > Linux kernel commit c7acec71. Unlike the original kernel patch we
> > did not add that even stronger type checking by using macro
> > BUILD_BUG_ON_MSG. So basically we removed a useful warning when
> > compiling such broken code:
> >
> >       struct st {
> >             int a;
> >             char b;
> >       };
> >       struct st t = { .a = 1, .b = 2 };
> >       struct st *x = container_of(&t.a, struct st, b);
> >       printf("%p %p\n", (void *)&t, (void *)x);
> >
> > Moreover we also introduced a new compiler warning for intel/icc:
> >    "arithmetic on pointer to void or function type"
> >
> > Let's just revert the update of container_of() because adding a
> > kernel-like BUILD_BUG_ON_MSG would be too much noise and also
> > problematic (see kernel commit c03567a8). Also note that the
> > original problem addressed by the kernel commit seems to be only
> > reproducible with gcc 4.9, not with any later gcc nor clang,icc.
> > Moreover, currently we have no such use-case in the UL sources
> > anyways.
>
> Interesting, I do not see any issue with list_entry(() now ;-)


BTW this is a nice webtool where you can see the issues quickly:

https://godbolt.org/z/Z2XvPc

cu,
Rudi