Re: [PATCH] net: fix IPv4 cksum simple function

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Nov 05, 2024 at 11:49:52AM +0100, David Marchand wrote:
> On Tue, Nov 5, 2024 at 11:20 AM Morten Brørup <mb@smartsharesystems.com> wrote:
> > > But there is still the question of packed structures with MSVC.
> > > Tyler proposal seemed to rely on the current __rte_packed conventional
> > > position.
> > > https://patchwork.dpdk.org/project/dpdk/patch/1713225913-20792-2-git-
> > > send-email-roretzla@linux.microsoft.com/
> > > Note that I am not a fan of this push/pop stuff.
> > >
> > > Maybe Andre will find a better solution.
> >
> > If we cannot come up with a clean solution that looks like an attribute (like GCC), we should accept MSVC's style with push/pop and learn to live with it.
> 
> Well, there is probably not many solutions.
> OVS does the same as what you suggest.
> 
> 
> >
> > Perhaps something like:
> >
> > #ifdef RTE_TOOLCHAIN_MSVC
> > #define __RTE_PACKED(...) \
> > __pragma(pack(push, 1)) \
> > __VA_ARGS__ \
> > __pragma(pack(pop))
> > #else
> > #define __RTE_PACKED(...) __VA_ARGS__ __attribute__((__packed__))
> > #endif
> >
> > This would also move the "packed" information to the top of the struct, making the code easier to read - i.e. easier to notice that the structure is packed when not hidden away at the end of the structure.
> 
> __RTE_PACKED(struct __rte_aligned(2) rte_ipv4_hdr {
> ...
> });
> 
> Agreed, looks better.
> 
Not convinced it looks better myself. Rather than packing the structure,
can we instead put aligned(2) on the 32-bit fields inside it?

/Bruce