On Tue, Nov 19, 2024 at 11:00:56AM +0000, Konstantin Ananyev wrote: > > > > -----Original Message----- > > From: Morten Brørup <m...@smartsharesystems.com> > > Sent: Tuesday, November 19, 2024 8:32 AM > > To: Andre Muezerie <andre...@linux.microsoft.com>; > > roret...@linux.microsoft.com; techbo...@dpdk.org > > Cc: yuying.zh...@intel.com; aman.deep.si...@intel.com; > > anatoly.bura...@intel.com; bruce.richard...@intel.com; > > byron.mar...@intel.com; conor.wa...@intel.com; > > cristian.dumitre...@intel.com; david.h...@intel.com; dev@dpdk.org; > > dsosnow...@nvidia.com; gak...@marvell.com; jer...@marvell.com; > > jingjing...@intel.com; kirill.rybalche...@intel.com; > > konstantin.v.anan...@yandex.ru; ma...@nvidia.com; or...@nvidia.com; > > radu.nico...@intel.com; ruifeng.w...@arm.com; > > sameh.gobr...@intel.com; sivaprasad.tumm...@amd.com; sk...@marvell.com; > > step...@networkplumber.org; > > suanmi...@nvidia.com; vattun...@marvell.com; viachesl...@nvidia.com; > > vladimir.medved...@intel.com; > > yipeng1.w...@intel.com > > Subject: RE: [PATCH v5 01/16] eal: provide pack start macro for MSVC > > > > > From: Andre Muezerie [mailto:andre...@linux.microsoft.com] > > > Sent: Tuesday, 19 November 2024 05.35 > > > > > > From: Tyler Retzlaff <roret...@linux.microsoft.com> > > > > > > MSVC struct packing is not compatible with GCC. Provide a macro that > > > can be used to push existing pack value and sets packing to 1-byte. > > > The existing __rte_packed macro is then used to restore the pack value > > > prior to the push. > > > > > > Instead of providing macros exclusively for MSVC and for GCC the > > > existing macro is deliberately utilized to trigger a warning if no > > > existing packing has been pushed allowing easy identification of > > > locations where the __rte_msvc_pack is missing. > > > > > > Signed-off-by: Tyler Retzlaff <roret...@linux.microsoft.com> > > > --- > > > lib/eal/include/rte_common.h | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/lib/eal/include/rte_common.h > > > b/lib/eal/include/rte_common.h > > > index 4d299f2b36..409890863e 100644 > > > --- a/lib/eal/include/rte_common.h > > > +++ b/lib/eal/include/rte_common.h > > > @@ -103,8 +103,10 @@ typedef uint16_t unaligned_uint16_t; > > > * Force a structure to be packed > > > */ > > > #ifdef RTE_TOOLCHAIN_MSVC > > > -#define __rte_packed > > > +#define __rte_msvc_pack __pragma(pack(push, 1)) > > > +#define __rte_packed __pragma(pack(pop)) > > > #else > > > +#define __rte_msvc_pack > > > #define __rte_packed __attribute__((__packed__)) > > > #endif > > > > > > -- > > > 2.47.0.vfs.0.3 > > > > Before proceeding with this, can we please discuss the alternative, > > proposed here: > > https://inbox.dpdk.org/dev/cajfav8ystgibbe+nkt9mc30r0+zp64_kgurhozqd90rd2hx...@mail.gmail.com/ > > > > The definition of the packing macro in OVS, for reference: > > https://github.com/openvswitch/ovs/blob/main/include/openvswitch/compiler.h#L209 > > Yes, that one looks much nicer to me too. > Could I also ask to avoid creeping _msvc_ into DPDK namespace. >
These are all good comments. I'll look more into it. > > > > The current solution requires __rte_packed to be placed at the end of a > > structure, although __attribute__((packed)) is normally > > allowed at the beginning (between the "struct" tag and the name of the > > structure), which introduces a high risk of contributors placing > > it "incorrectly", thus causing errors. > > > > I have a strong preference for an __RTE_PACKED(decl) variant. > > > > Here's a third alternative: > > #ifdef RTE_TOOLCHAIN_MSVC > > #define __rte_msvc_pack_begin __pragma(pack(push, 1)) > > #define __rte_msvc_pack_end __pragma(pack(pop)) > > #else > > #define __rte_msvc_pack_begin > > #define __rte_msvc_pack_end > > #endif > > > > The third alternative is also problematic, e.g. if a contributor forgets > > the _end after the structure declaration, or adds another > > structure declaration before the _end. > > > > -Morten
