Re: [dpdk-dev] [PATCH] ixgbe: fix clang compile - remove truncation errors

[Neil Horman <nhorman@tuxdriver.com>]

On Fri, Nov 28, 2014 at 03:31:00PM +0000, Bruce Richardson wrote:
> When compiling with clang, errors were being emitted due to truncation
> of values when assigning to the tx_offload_mask bit fields.
> 
> dpdk.org/lib/librte_pmd_ixgbe/ixgbe_rxtx.c:404:27: fatal error: implicit truncation from 'int' to bitfield changes value from -1 to 127 [-Wbitfield-constant-conversion]
> 		    tx_offload_mask.l2_len = ~0;
> 
> The fix proposed here is to define a static const value of the same type
> with all fields set to 1s, and use that instead of constants for assigning to.
> 
> Other options would be to explicitily define the suitable constants that
> would not truncate for each individual field e.g. 0x7f for l2_len, 0x1FF
> for l3_len, etc., but this solution here has the advantage that it works
> without any changes to values if the field sizes are ever modified.
> 
> Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> ---
>  lib/librte_pmd_ixgbe/ixgbe_rxtx.c | 29 +++++++++++++++--------------
>  1 file changed, 15 insertions(+), 14 deletions(-)
> 
> diff --git a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
> index 8559ef6..4f71194 100644
> --- a/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
> +++ b/lib/librte_pmd_ixgbe/ixgbe_rxtx.c
> @@ -367,6 +367,7 @@ ixgbe_set_xmit_ctx(struct igb_tx_queue* txq,
>  		volatile struct ixgbe_adv_tx_context_desc *ctx_txd,
>  		uint64_t ol_flags, union ixgbe_tx_offload tx_offload)
>  {
> +	static const union ixgbe_tx_offload offload_allones = { .data = ~0 };
Do you want to make this a static data structure?  If you make it a macro like
this:
#define ALLONES {.data = ~0}
Then you save the extra data space in the .data area (not that its that much),
and you can define it in a header file and use it in multiple c files (if you
need to)
Neil