Re: [PATCH 4/4] signals/sigaltstack: Change SS_AUTODISARM to (1U << 31)

[Stas Sergeev]

03.05.2016 20:31, Andy Lutomirski ÐÐÑÐÑ:
> Using bit 4 divides the space of available bits strangely.  Use bit
> 31 instead so that we have a better chance of keeping flag and mode
> bits separate in the long run.
>
> Cc: Stas Sergeev <stsp@xxxxxxx>
> Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
> Cc: Aleksa Sarai <cyphar@xxxxxxxxxx>
> Cc: Amanieu d'Antras <amanieu@xxxxxxxxx>
> Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> Cc: Borislav Petkov <bp@xxxxxxxxx>
> Cc: Brian Gerst <brgerst@xxxxxxxxx>
> Cc: Denys Vlasenko <dvlasenk@xxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Cc: H. Peter Anvin <hpa@xxxxxxxxx>
> Cc: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> Cc: Jason Low <jason.low2@xxxxxx>
> Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
> Cc: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
> Cc: Palmer Dabbelt <palmer@xxxxxxxxxxx>
> Cc: Paul Moore <pmoore@xxxxxxxxxx>
> Cc: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Richard Weinberger <richard@xxxxxx>
> Cc: Sasha Levin <sasha.levin@xxxxxxxxxx>
> Cc: Shuah Khan <shuahkh@xxxxxxxxxxxxxxx>
> Cc: Tejun Heo <tj@xxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Vladimir Davydov <vdavydov@xxxxxxxxxxxxx>
> Cc: linux-api@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxx>
> ---
>   include/uapi/linux/signal.h               | 2 +-
>   tools/testing/selftests/sigaltstack/sas.c | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/uapi/linux/signal.h b/include/uapi/linux/signal.h
> index 738826048af2..cd0804b6bfa2 100644
> --- a/include/uapi/linux/signal.h
> +++ b/include/uapi/linux/signal.h
> @@ -8,7 +8,7 @@
>   #define SS_DISABLE	2
>   
>   /* bit-flags */
> -#define SS_AUTODISARM	(1 << 4)	/* disable sas during sighandling */
> +#define SS_AUTODISARM	(1U << 31)	/* disable sas during sighandling */
And what if we are out of 32 bits for storing both mode and flags? :)
Well, yes, very unlikely, but I did it that way exactly so that
we can eventually promote to 64bit variable.
Doesn't matter at all, of course. Let it be any way you like.