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

[Olivier MATZ <olivier.matz@6wind.com>]

Hi Bruce, Hi Neil,

On 11/30/2014 02:05 AM, Neil Horman wrote:
> 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)

I found that the following code works:

	tx_offload_mask.l2_len |= ~0;

(note the '|=' instead of '=')

I would avoid to create a macro. What do you think?

Regards,
Olivier