Re: [Minios-devel] [UNIKRAFT PATCH v4 02/16] include/uk/arch: assert for undefined behavior in ffs-functions

[Florian Schmidt <Florian.Schmidt@xxxxxxxxx>]

After discussing this with Simon and Sharan, I suggest to remove this 
patch from the series and postpone it. (It's stand-alone, so removing 
this doesn't hurt the rest of the series.) I know I asked for some sort 
of assertion mechanism for this, but it seems there is still some open 
discussion of how exactly to implement it for functions in the 
include/uk/ hierarchy.
Cheers,
Florian

On 09/06/2018 03:48 PM, Yuri Volchkov wrote:
> The behavior of bitops functions in unikraft is undefined, if the
> first/last bit is searched, while none is set (zero is passed as an
> argument). This patch adds an assertion if argument is 0
>
> Signed-off-by: Yuri Volchkov <yuri.volchkov@xxxxxxxxx>
> ---
>   include/uk/arch/x86_64/atomic.h | 18 ++++++++++++++++++
>   1 file changed, 18 insertions(+)
>
> diff --git a/include/uk/arch/x86_64/atomic.h b/include/uk/arch/x86_64/atomic.h
> index c48d5bd..7bab838 100644
> --- a/include/uk/arch/x86_64/atomic.h
> +++ b/include/uk/arch/x86_64/atomic.h
> @@ -30,6 +30,16 @@
>   #error Do not include this header directly
>   #endif
>   
> +#ifdef CONFIG_LIBUKDEBUG
> +#include <uk/assert.h>
> +#define __ukarch_atomic_assert(x) UK_ASSERT(x)
> +#else
> +#define __ukarch_atomic_assert(x) \
> +       do {               \
> +       } while (0)
> +#endif /* CONFIG_LIBUKDEBUG */
> +
> +
>   /**
>    * ukarch_ffs - find first (lowest) set bit in word.
>    * @word: The word to search
> @@ -38,6 +48,8 @@
>    */
>   static inline unsigned int ukarch_ffs(unsigned int word)
>   {
> +       __ukarch_atomic_assert(word);
> +
>         __asm__("bsfl %1,%0"
>                 : "=r" (word)
>                 : "rm" (word));
> @@ -52,6 +64,8 @@ static inline unsigned int ukarch_ffs(unsigned int word)
>    */
>   static inline unsigned int ukarch_fls(unsigned int word)
>   {
> +       __ukarch_atomic_assert(word);
> +
>         __asm__("bsrl %1,%0"
>                 : "=r" (word)
>                 : "rm" (word));
> @@ -66,6 +80,8 @@ static inline unsigned int ukarch_fls(unsigned int word)
>    */
>   static inline unsigned long ukarch_ffsl(unsigned long word)
>   {
> +       __ukarch_atomic_assert(word);
> +
>         __asm__("bsfq %1,%0"
>                 : "=r" (word)
>                 : "rm" (word));
> @@ -80,6 +96,8 @@ static inline unsigned long ukarch_ffsl(unsigned long word)
>    */
>   static inline unsigned long ukarch_flsl(unsigned long word)
>   {
> +       __ukarch_atomic_assert(word);
> +
>         __asm__("bsrq %1,%0"
>                 : "=r" (word)
>                 : "rm" (word));
--
Dr. Florian Schmidt
フローリアン・シュミット
Research Scientist,
Systems and Machine Learning Group
NEC Laboratories Europe
Kurfürsten-Anlage 36, D-69115 Heidelberg
Tel.     +49 (0)6221 4342-265
Fax:     +49 (0)6221 4342-155
e-mail:  florian.schmidt@xxxxxxxxx
============================================================
Registered at Amtsgericht Mannheim, Germany, HRB728558

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