Re: [Minios-devel] [UNIKRAFT PATCH 2/2] lib/uknetdev: Fix compliation warning about signed/unsigned comparision

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 11/10/2019 09:52, Jia He wrote:
> This fixes the compliation warning when compiling libuknetdev
Typo s/compliation/compilation/

> /root/hj/UK/unikraft/lib/uknetdev/netbuf.c: In function
> 'uk_netbuf_alloc_buf':
> /root/hj/UK/unikraft/lib/uknetdev/netbuf.c:120:35: warning: comparison
> between signed and unsigned integer expressions [-Wsign-compare]
>    if (likely(UINT16_MAX - headroom > NETBUF_ADDR_ALIGNMENT)) {
>                                     ^
> /root/hj/UK/unikraft/include/uk/arch/lcpu.h:48:43: note: in definition
> of macro 'likely'
>   #define likely(x)   (__builtin_expect((!!(x)), 1))
>                                             ^
> Signed-off-by: Jia He <justin.he@xxxxxxx>
> ---
>   lib/uknetdev/netbuf.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/lib/uknetdev/netbuf.c b/lib/uknetdev/netbuf.c
> index 96a5f68..108bd36 100644
> --- a/lib/uknetdev/netbuf.c
> +++ b/lib/uknetdev/netbuf.c
> @@ -36,7 +36,7 @@
>   #include <uk/print.h>
>   
>   /* Used to align netbuf's priv and data areas to `long long` data type */
> -#define NETBUF_ADDR_ALIGNMENT (sizeof(long long))
> +#define NETBUF_ADDR_ALIGNMENT (int)(sizeof(long long))
Maybe I am missing something but:

UINT16_MAX - headrom should be unsigned, right?

IIRC, sizeof() is also returning an unsigned. So how this is solving the problem 
here?
>   #define NETBUF_ADDR_ALIGN_UP(x) ALIGN_UP((x), NETBUF_ADDR_ALIGNMENT)
>   
>   void uk_netbuf_init_indir(struct uk_netbuf *m,
Cheers,

--
Julien Grall

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