Re: [PATCH v3 2/2] stack: enable build with MSVC

[Andre Muezerie <andremue@linux.microsoft.com>]

On Tue, Feb 04, 2025 at 10:30:03AM +0000, Bruce Richardson wrote:
> On Mon, Feb 03, 2025 at 05:58:38PM -0800, Andre Muezerie wrote:
> > An implementation compatible with MSVC is provided for
> > atomic128_cmp_exchange in rte_stack_lf_c11.h.
> > 
> > Now that the issues preventing the code needed to build lib/stack
> > have been addressed, it can be enabled so that it also gets built
> > when using the MSVC compiler.
> > 
> > Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
> > ---
> >  lib/stack/meson.build        |  6 ------
> >  lib/stack/rte_stack_lf_c11.h | 27 +++++++++++++++++++++++++++
> >  2 files changed, 27 insertions(+), 6 deletions(-)
> > 
> > diff --git a/lib/stack/meson.build b/lib/stack/meson.build
> > index 7631a14784..18177a742f 100644
> > --- a/lib/stack/meson.build
> > +++ b/lib/stack/meson.build
> > @@ -1,12 +1,6 @@
> >  # SPDX-License-Identifier: BSD-3-Clause
> >  # Copyright(c) 2019 Intel Corporation
> >  
> > -if is_ms_compiler
> > -    build = false
> > -    reason = 'not supported building with Visual Studio Toolset'
> > -    subdir_done()
> > -endif
> > -
> >  sources = files('rte_stack.c', 'rte_stack_std.c', 'rte_stack_lf.c')
> >  headers = files('rte_stack.h')
> >  # subheaders, not for direct inclusion by apps
> > diff --git a/lib/stack/rte_stack_lf_c11.h b/lib/stack/rte_stack_lf_c11.h
> > index 60d46e963b..898d43edb2 100644
> > --- a/lib/stack/rte_stack_lf_c11.h
> > +++ b/lib/stack/rte_stack_lf_c11.h
> > @@ -8,6 +8,33 @@
> >  #include <rte_branch_prediction.h>
> >  #include <rte_prefetch.h>
> >  
> > +#ifdef RTE_TOOLCHAIN_MSVC
> > +/**
> > + * The maximum lock-free data size that can be manipulated atomically using C11
> > + * standard is limited to 8 bytes.
> > + *
> > + * This implementation for rte_atomic128_cmp_exchange operates on 16-byte
> > + * data types and is made available here so that it can be used without the
> > + * need to unnecessarily expose other non-C11 atomics present in
> > + * rte_atomic_64.h when using MSVC.
> > + */
> > +static inline int
> > +rte_atomic128_cmp_exchange(rte_int128_t *dst,
> > +			   rte_int128_t *exp,
> > +			   const rte_int128_t *src,
> > +			   unsigned int weak,
> > +			   int success,
> > +			   int failure)
> > +{
> > +	return (int)_InterlockedCompareExchange128(
> > +		(int64_t volatile *) dst,
> > +		src->val[1], /* exchange high */
> > +		src->val[0], /* exchange low */
> > +		(int64_t *) exp /* comparand result */
> > +	);
> > +}
> > +#endif /* RTE_TOOLCHAIN_MSVC */
> > +
> 
> Is there a particular reason for having this only in the stack library,
> more than more generically available?
> 
> /Bruce

The PR history shows that the intention with MSVC (which is a new toolchain/platform)
was to block visibility of the rte_atomic APIs from day 1.

More details can be seen here:
https://github.com/JoverZhang/dpdk/pull/21/commits/27da6a1234148fef43687d324ab2221df0631b5c

If there's a strong need we could revert that decision, but for now it seems it
would be better to follow the established direction.
--
Andre Muezerie