[CRIU] [PATCH] sfds: Fix UB in choose_service_fd_base due to calling __builtin_clz(0)

[Andrei Vagin]

Applied, thanks!

On Tue, Apr 10, 2018 at 01:35:04PM +0300, Kirill Tkhai wrote:
> From: Radoslaw Burny <rburny at google.com>
> 
> __builtin_clz(0) leads to undefined behaviour:
> https://gcc.gnu.org/onlinedocs/gcc/Other-Builtins.html
> 
> Set nr = 1 directly to avoid this.
> 
> Link: https://github.com/checkpoint-restore/criu/issues/470
> Signed-off-by: Radoslaw Burny <rburny at google.com>
> Acked-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/util.c |    5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/criu/util.c b/criu/util.c
> index b19bf5175..46d67eca6 100644
> --- a/criu/util.c
> +++ b/criu/util.c
> @@ -589,7 +589,10 @@ static int choose_service_fd_base(struct pstree_item *me)
>  	real_nr = nr;
>  
>  	nr /= (1024 / sizeof(void *));
> -	nr = 1 << (32 - __builtin_clz(nr));
> +	if (nr)
> +		nr = 1 << (32 - __builtin_clz(nr));
> +	else
> +		nr = 1;
>  	nr *= (1024 / sizeof(void *));
>  
>  	if (nr > service_fd_rlim_cur) {
>