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

["Justin He (Arm Technology China)" <Justin.He@xxxxxxx>]

Hi Julien

> -----Original Message-----
> From: Julien Grall <julien.grall@xxxxxxx>
> Sent: Friday, October 11, 2019 5:00 PM
> To: Justin He (Arm Technology China) <Justin.He@xxxxxxx>; minios-
> devel@xxxxxxxxxxxxxxxxxxxx; Simon Kuenzer <simon.kuenzer@xxxxxxxxx>;
> Costin Lupu <costin.lupu@xxxxxxxxx>
> Cc: Sharan.Santhanam@xxxxxxxxx; Felipe Huici <felipe.huici@xxxxxxxxx>;
> Kaly Xin (Arm Technology China) <Kaly.Xin@xxxxxxx>;
> Santiago.Pagani@xxxxxxxxx; nd <nd@xxxxxxx>
> Subject: Re: [UNIKRAFT PATCH 2/2] lib/uknetdev: Fix compliation warning
> about signed/unsigned comparision
> 
> 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?
Because UINT16_MAX and headroom are both unsigned short,
Integer types smaller than int are promoted when an operation is
performed on them. Thus, the left side of equation is "int", and 
the right side is size_t.


--
Cheers,
Justin (Jia He)


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