Re: [Minios-devel] [UNIKRAFT PATCH v2 2/2] lib/uknetdev: Fix compliation warning about signed/unsigned comparision

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

Title: s/compliation/compilation/

On 12/10/2019 07:39, Jia He wrote:
> This fixes the compilation warning when compiling libuknetdev
>
> /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))
>                                             ^
>
> The UINT16_MAX is 0xffff (signed int) on my X86 host (gcc version 7.4.0).
I am a bit confused, is this cross-compilation or native compilation? I guess 
the later as you mention x86 host. So I guess you are referring to 
/usr/include/stdint.h, right?
> 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.
I am not sure to understand this. Above you say UINT16_MAX is signed int (aka 
int), so why do you speak about promotion to int here?
Cheers,

--
Julien Grall




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