[dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing

[Ananyev, Konstantin]

Hi Daniel,
So for my own curiosity: what went wrong here?
Did compiler avoid to generate a code for while {} loop?
Or something else?
BTW, it is an internal function, so instead of introducing new typedef,
we can just change the type of buf?
Let say to uint8_t *?
>From gcc manual page: "  A character type may alias any other type."
Would that work?
Konstantin

> -----Original Message-----
> From: dev [mailto:dev-bounces at dpdk.org] On Behalf Of Daniel Mrzyglod
> Sent: Tuesday, November 24, 2015 4:31 PM
> To: dev at dpdk.org
> Subject: [dpdk-dev] [PATCH v2] net: fix build with gcc 4.4.7 and strict aliasing
> 
> This fix is for IPv6 checksum offload error on RHEL65.
> Any optimalisation above -O0 provide error in IPv6 checksum
> flag "-fstrict-aliasing" is default for optimalisation above -O0.
> 
> Fixes: 2b039d5f20a3 ("net: fix build with gcc 4.4.7 and strict aliasing")
> 
> Signed-off-by: Daniel Mrzyglod <danielx.t.mrzyglod at intel.com>
> ---
>  lib/librte_net/rte_ip.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/librte_net/rte_ip.h b/lib/librte_net/rte_ip.h
> index 71c519a..5b7554a 100644
> --- a/lib/librte_net/rte_ip.h
> +++ b/lib/librte_net/rte_ip.h
> @@ -169,7 +169,8 @@ __rte_raw_cksum(const void *buf, size_t len, uint32_t sum)
>  {
>  	/* workaround gcc strict-aliasing warning */
>  	uintptr_t ptr = (uintptr_t)buf;
> -	const uint16_t *u16 = (const uint16_t *)ptr;
> +	typedef uint16_t __attribute__((__may_alias__)) u16_p;
> +	const u16_p *u16 = (const u16_p *)ptr;
> 
>  	while (len >= (sizeof(*u16) * 4)) {
>  		sum += u16[0];
> --
> 2.5.0