Re: [PATCH] kernel/compat.c: mark expected switch fall-throughs

From: Arnd Bergmann
Date: Tue Apr 16 2019 - 04:33:16 EST

On Tue, Apr 16, 2019 at 9:29 AM Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx> wrote:
> In preparation to enabling -Wimplicit-fallthrough, mark switch cases
> where we are expecting to fall through.
> This patch aims to suppress up to 3 missing-break-in-switch false
> positives on some architectures.
> Cc: Arnd Bergmann <arnd@xxxxxxxx>
> Cc: Deepa Dinamani <deepa.kernel@xxxxxxxxx>
> Cc: Gustavo A. R. Silva <gustavo@xxxxxxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: Jann Horn <jannh@xxxxxxxxxx>
> Signed-off-by: Stephen Rothwell <sfr@xxxxxxxxxxxxxxxx>

Acked-by: Arnd Bergmann <arnd@xxxxxxxx>

> ---
> kernel/compat.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
> I know that this makes the lines longer than 80 characters, but I
> though that this was better than adding new lines.

It's a bit inconsistent though since put_compat_sigset() has the
comments in separate lines, as of commit 89976005536c
("include/linux/compat.h: mark expected switch fall-throughs").

I don't care either way, but it might be better to do it the same way
for both.

We could also consider just getting rid of put_compat_sigset() and
get_compat_sigset() but replacing them with a combined
put_sigset()/get_sigset() that does the right thing for both native
and compat tasks. This lets us kill a couple of compat system
calls that only differ in their sigset_t argument. On little-endian
systems (which are the vast majority of the installed base), there
is no difference anyway there is no overhead anyway since
native and compat sigset_t are identical.