Re: [dpdk-dev] [PATCH 2/3] crypto: fix pedentic compilation errors

["De Lara Guarch, Pablo" <pablo.de.lara.guarch@intel.com>]

> -----Original Message-----
> From: Gaëtan Rivet [mailto:gaetan.rivet@6wind.com]
> Sent: Wednesday, November 22, 2017 2:32 PM
> To: Neil Horman <nhorman@tuxdriver.com>
> Cc: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>; Akhil Goyal
> <akhil.goyal@nxp.com>; Doherty, Declan <declan.doherty@intel.com>;
> dev@dpdk.org; De Lara Guarch, Pablo <pablo.de.lara.guarch@intel.com>;
> stable@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 2/3] crypto: fix pedentic compilation errors
> 
> On Wed, Nov 22, 2017 at 08:56:14AM -0500, Neil Horman wrote:
> > On Wed, Nov 22, 2017 at 09:10:17AM +0100, Nelio Laranjeiro wrote:
> > >  /root/dpdk/x86_64-native-linuxapp-gcc/include/rte_crypto.h:126:28:
> error: ISO C forbids zero-size array ‘sym’ [-Werror=pedantic]
> > >    struct rte_crypto_sym_op sym[0];
> > >                             ^~~
> > >
> > > Fixes: d2a4223c4c6d ("cryptodev: do not store pointer to op specific
> > > params")
> > > Cc: pablo.de.lara.guarch@intel.com
> > > Cc: stable@dpdk.org
> > >
> > > Signed-off-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
> > > ---
> > >  lib/librte_cryptodev/rte_crypto.h | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/lib/librte_cryptodev/rte_crypto.h
> > > b/lib/librte_cryptodev/rte_crypto.h
> > > index 3d672fe7d..dc6e91d1d 100644
> > > --- a/lib/librte_cryptodev/rte_crypto.h
> > > +++ b/lib/librte_cryptodev/rte_crypto.h
> > > @@ -123,7 +123,7 @@ struct rte_crypto_op {
> > >
> > >  	RTE_STD_C11
> > >  	union {
> > > -		struct rte_crypto_sym_op sym[0];
> > > +		struct rte_crypto_sym_op *sym;
> > >  		/**< Symmetric operation parameters */
> > >  	}; /**< operation specific parameters */  };
> > > --
> > > 2.11.0
> > >
> > >
> > As Laura notes, this isn't the right solution.  In addition to adding a 64 bit
> > pointer, it I think also results in incorrect semantics.  That is to say, the
> > allocation path for this structure allocates the rte_crypto_op and
> additional
> > memory for the sym array contiguously, which the sym[0] syntax
> correctly
> > interprets to mean the storage for the array is inline with the structure.
> > Changing to a pointer means you are using the first elements of the array
> > storage as your pointer, which could be filled with any old value, leading
> to
> > corruption.
> >
> > If you can't use zero length array semantics (which I assume you cant, as I
> > don't think clang supports that), a better soution might be to remove the
> sym
> > variable entirely, and replace it with a macro that access the sym array as
> an
> > offset from the start of the pointer.  That would seem to be an ABI
> change, but
> > if you went through that process you would wind up with the same sized
> struct,
> > which would be nice
> >
> > Neil
> >
> 
> ISO C forbids zero-size arrays, but ISO C99 allows flexible arrays.
> Why is this symbole within a union? Why not remove the union, change
> sym[0] to sym[]?

It is a union because there were going to be other types of crypto operations (might still happen in the future).
For instance:

union{
	struct rte_crypto_sym_op sym[0];
	struct rte_crypto_asym_op asym[0];
}

Thanks,
Pablo
> 
> --
> Gaëtan Rivet
> 6WIND