Re: [PATCH] asm-generic: bug.h: add unreachable() in BUG() for CONFIG_BUG not set

[Randy Dunlap]

On 10/17/21 12:09 PM, Arnd Bergmann wrote:
> On Sun, Oct 17, 2021 at 7:49 PM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
> > When CONFIG_BUG is not set/enabled, there is a warning
> > on ARCH=m68k, gcc version 11.1.0-nolibc from Arnd's crosstools:
> >
> > ../fs/afs/dir.c: In function 'afs_dir_set_page_dirty':
> > ../fs/afs/dir.c:51:1: error: no return statement in function returning non-void [-Werror=return-type]
> >
> > Adding "unreachable()" in the BUG() macro silences the warning.
>
> No, I don't think this is the right solution:
>
> > -#define BUG() do {} while (1)
> > +#define BUG() do {unreachable();} while (1)
>
> Marking this code unreachable() means the compiler is free
> to assume any code path leading here will never be entered,
> which leads to additional undefined behavior and other warnings
> rather than just hanging reproducibly.
>
> The endless loop here should normally be sufficient to tell the
> compiler that the function never returns, so it sounds like a
> problem in gcc for m68k.

Sounds likely.

> Did you see any other issues like this one on m68k, or the
> same one on another architecture?

No and no.

thanks.
--
~Randy