Re: [dpdk-dev] [PATCH] net: fix compilation with pedantic enabled

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

Hi,

On Tue, Jul 21, 2020 at 01:05:57AM +0100, Ferruh Yigit wrote:
> On 7/16/2020 1:12 PM, Raslan Darawsheh wrote:
> > when trying to compile rte_mpls with pedantic enabled,
> > it will complain about bit field defintion.
> > error: type of bit-field 'bs' is a GCC extension [-Werror=pedantic]
> > error: type of bit-field 'tc' is a GCC extension [-Werror=pedantic]
> > error: type of bit-field 'tag_lsb' is a GCC extension [-Werror=pedantic]
> '
> I tried to reproduce by adding to '-pedantic' to 'rte_net.c' (which uses
> 'rte_mpls.h') but not able to get the warning. Is this happen with specific
> version of the compiler?
> 
> > 
> > This fixes the compilation error.
> > 
> > Fixes: e480cf487a0d ("net: add MPLS header structure")
> > Cc: olivier.matz@6wind.com
> > Cc: stable@dpdk.org
> > 
> > Signed-off-by: Raslan Darawsheh <rasland@mellanox.com>
> > ---
> >  lib/librte_net/rte_mpls.h | 12 ++++++------
> >  1 file changed, 6 insertions(+), 6 deletions(-)
> > 
> > diff --git a/lib/librte_net/rte_mpls.h b/lib/librte_net/rte_mpls.h
> > index db91707..ecd1f64 100644
> > --- a/lib/librte_net/rte_mpls.h
> > +++ b/lib/librte_net/rte_mpls.h
> > @@ -24,13 +24,13 @@ extern "C" {
> >  struct rte_mpls_hdr {
> >  	uint16_t tag_msb;   /**< Label(msb). */
> >  #if RTE_BYTE_ORDER == RTE_BIG_ENDIAN
> > -	uint8_t tag_lsb:4;  /**< Label(lsb). */
> > -	uint8_t tc:3;       /**< Traffic class. */
> > -	uint8_t bs:1;       /**< Bottom of stack. */
> > +	uint32_t tag_lsb:4;  /**< Label(lsb). */
> > +	uint32_t tc:3;       /**< Traffic class. */
> > +	uint32_t bs:1;       /**< Bottom of stack. */
> >  #else
> > -	uint8_t bs:1;       /**< Bottom of stack. */
> > -	uint8_t tc:3;       /**< Traffic class. */
> > -	uint8_t tag_lsb:4;  /**< label(lsb) */
> > +	uint32_t bs:1;       /**< Bottom of stack. */
> > +	uint32_t tc:3;       /**< Traffic class. */
> > +	uint32_t tag_lsb:4;  /**< label(lsb) */
> >  #endif
> >  	uint8_t  ttl;       /**< Time to live. */
> >  } __rte_packed;
> 
> The struct size keeps same after change, do you know if this behavior is part of
> standard and guaranteed?

I have the same fear.

Would it make sense to add __extension__ instead? We already do that
for gre, for instance.