On Mon, Feb 26, 2024 at 01:23:35PM +0000, Konstantin Ananyev wrote:
>
>
> >
> > The current location used for __rte_aligned(a) for alignment of types
> > and variables is not compatible with MSVC. There is only a single
> > location accepted by both toolchains.
> >
> > For variables standard C11 offers alignas(a) supported by conformant
> > compilers i.e. both MSVC and GCC.
> >
> > For types the standard offers no alignment facility that compatibly
> > interoperates with C and C++ but may be achieved by relocating the
> > placement of __rte_aligned(a) to the aforementioned location accepted
> > by all currently supported toolchains.
> >
> > To allow alignment for both compilers do the following:
> >
> > * Move __rte_aligned from the end of {struct,union} definitions to
> > be between {struct,union} and tag.
> >
> > The placement between {struct,union} and the tag allows the desired
> > alignment to be imparted on the type regardless of the toolchain being
> > used for all of GCC, LLVM, MSVC compilers building both C and C++.
> >
> > * Replace use of __rte_aligned(a) on variables/fields with alignas(a).
> >
> > Signed-off-by: Tyler Retzlaff <roret...@linux.microsoft.com>
> > Acked-by: Morten Brørup <m...@smartsharesystems.com>
> > ---
> > lib/ring/rte_ring_core.h | 16 +++++++++-------
> > lib/ring/rte_ring_peek_zc.h | 4 ++--
> > 2 files changed, 11 insertions(+), 9 deletions(-)
> >
> > diff --git a/lib/ring/rte_ring_core.h b/lib/ring/rte_ring_core.h
> > index b770873..497d535 100644
> > --- a/lib/ring/rte_ring_core.h
> > +++ b/lib/ring/rte_ring_core.h
> > @@ -19,6 +19,8 @@
> > * instead.
> > */
> >
> > +#include <stdalign.h>
> > +
> > #ifdef __cplusplus
> > extern "C" {
> > #endif
> > @@ -78,7 +80,7 @@ struct rte_ring_headtail {
> >
> > union __rte_ring_rts_poscnt {
> > /** raw 8B value to read/write *cnt* and *pos* as one atomic op */
> > - RTE_ATOMIC(uint64_t) raw __rte_aligned(8);
> > + alignas(8) RTE_ATOMIC(uint64_t) raw;
>
> One small question - here and below, would it possible to do
> 'alignas(sizeof(uint64_t))' instead of 'alignas(8)?
> Or MSVC has some restrictions here?
it should be okay to use a constant expression with alignas(n) even with
MSVC because it is conformant, if it isn't it would be a bug. it is one benefit
over using __declspec(align(a)).
i'll update the series to use sizeof.
>
>
> > struct {
> > uint32_t cnt; /**< head/tail reference counter */
> > uint32_t pos; /**< head/tail position */
> > @@ -94,7 +96,7 @@ struct rte_ring_rts_headtail {
> >
