Re: [Minios-devel] [UNIKRAFT PATCH] lib/ukalloc: fix wrong return value in uk_malloc_ifpages

[Simon Kuenzer <simon.kuenzer@xxxxxxxxx>]

Hey Florian,

On 24.08.2018 13:23, Florian Schmidt wrote:
> uk_malloc_ifpages returned the wrong pointer, because it added
> sizeof(size_t) to a pointer of type size_t. Hence, the return value
> wasn't offset from intptr by size_t bytes, but by size_t*size_t bytes.
>
> This patch makes intptr a void* in places in which its property as
> size_t* isn't used.
>
> Signed-off-by: Florian Schmidt <florian.schmidt@xxxxxxxxx>
> ---
>   lib/ukalloc/alloc.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/lib/ukalloc/alloc.c b/lib/ukalloc/alloc.c
> index 52e9a77..2f5e364 100644
> --- a/lib/ukalloc/alloc.c
> +++ b/lib/ukalloc/alloc.c
> @@ -167,7 +167,7 @@ static inline size_t uk_alloc_size_to_order(size_t size)
>   
>   void *uk_malloc_ifpages(struct uk_alloc *a, size_t size)
>   {
> -       size_t *intptr;
> +       void *intptr;
>         size_t order;
>         size_t realsize = sizeof(order) + size;
>   
> @@ -181,7 +181,7 @@ void *uk_malloc_ifpages(struct uk_alloc *a, size_t size)
>         if (!intptr)
>                 return NULL;
>   
> -	*intptr = order;
> +       *(size_t *)intptr = order;
>         return intptr + sizeof(order);
Hum... pointer arithmetics on your calculation of your returned value 
was causing the problem. I somehow do not like that the solution is 
placed somewhere else in the function to make the return statement correct.
What if you would have done this on the return?:

return (void *)((uintptr_t)intptr + sizeof(order))

Or you could declare intptr as uintptr_t. I think this is clearer to 
understand what it going on.
>   }
>   
> @@ -229,7 +229,7 @@ void *uk_realloc_ifpages(struct uk_alloc *a, void *ptr, size_t size)
>   int uk_posix_memalign_ifpages(struct uk_alloc *a,
>                                 void **memptr, size_t align, size_t size)
>   {
> -       size_t *intptr;
> +       void *intptr;
>         size_t realsize;
>         size_t order;
>   
> @@ -259,7 +259,7 @@ int uk_posix_memalign_ifpages(struct uk_alloc *a,
>         if (!intptr)
>                 return ENOMEM;
>   
> -	*intptr = order;
> +       *(size_t *)intptr = order;
>         *memptr = (void *) ALIGN_UP((uintptr_t)intptr + sizeof(order), align);
>         return 0;
>   }
Thanks,

Simon

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