On Mon, Jan 06, 2025 at 11:00:15AM +0000, Bruce Richardson wrote:
> On Fri, Jan 03, 2025 at 01:26:34PM -0800, Andre Muezerie wrote:
> > On Fri, Jan 03, 2025 at 11:24:02AM -0800, Stephen Hemminger wrote:
> > > On Fri, 3 Jan 2025 07:36:48 -0800
> > > Andre Muezerie <[email protected]> wrote:
> > >
> > > > From: Andre Muezerie <[email protected]>
> > > > To: [email protected]
> > > > Cc: [email protected], [email protected]
> > > > Subject: [PATCH v11 0/3] add diagnostics macros to make code portable
> > > > Date: Fri, 3 Jan 2025 07:36:48 -0800
> > > > X-Mailer: git-send-email 1.8.3.1
> > > >
> > > > It was a common pattern to have "GCC diagnostic ignored" pragmas
> > > > sprinkled over the code and only activate these pragmas for certain
> > > > compilers (gcc and clang). Clang supports GCC's pragma for
> > > > compatibility with existing source code, so #pragma GCC diagnostic
> > > > and #pragma clang diagnostic are synonyms for Clang
> > > > (https://clang.llvm.org/docs/UsersManual.html).
> > > >
> > > > Now that effort is being made to make the code compatible with MSVC
> > > > these expressions would become more complex. It makes sense to hide
> > > > this complexity behind macros. This makes maintenance easier as these
> > > > macros are defined in a single place. As a plus the code becomes
> > > > more readable as well.
> > >
> > > Since 90% of these cases are about removing const from a pointer,
> > > maybe it would be better to have a macro that did that?
> > >
> > > Would not work for base driver code which is pretending to be platform
> > > independent.
> >
> > Most of the warnings I've seen were about dropping the volatile qualifier,
> > like the one below:
> >
> > ../drivers/net/i40e/i40e_rxtx_vec_sse.c:42:32: warning: cast from 'volatile
> > struct i40e_32byte_rx_desc::(unnamed at
> > ../drivers/net/i40e/base/i40e_type.h:803:2) *' to
> > '__attribute__((__vector_size__(2 * sizeof(long long)))) long long *' drops
> > volatile qualifier [-Wcast-qual]
> > 42 | _mm_store_si128((__m128i
> > *)&rxdp[i].read,
> > | ^
> >
> > To make sure I understood your suggestion correctly, you're proposing to
> > replace this
> >
> > __rte_diagnostic_push
> > __rte_diagnostic_ignored_wcast_qual
> > _mm_store_si128((__m128i *)&rxdp[i].read, dma_addr0);
> > __rte_diagnostic_pop
> >
> >
> > with something like this?
> >
> > _mm_store_si128(RTE_IGNORE_CAST_QUAL((__m128i *)&rxdp[i].read),
> > dma_addr0);
> >
> > This could be done, and I think it does look better, despite the slight
> > line length increase.
>
> +1 for this option. One macro can be used to drop all qualifiers, both
> const and volatile, right?
Yes, a single macro can drop all qualifiers. I did realize though that the
macro must involve the entire expression - it cannot be used just around one
parameter, unfortunately.
It would look like:
RTE_IGNORE_CAST_QUAL(_mm_store_si128((__m128i *)&rxdp[i].read,
dma_addr0);)
This is still the same line length as before, but not as elegant.
For some code blocks where many consecutive lines (4+) would require this macro
I feel that it might still make sense to use
__rte_diagnostic_ignored_wcast_qual, because using RTE_IGNORE_CAST_QUAL might
result in additional lines anyways due to 80 column width limit. I'm planning
to submit a new version of the patchset with this mixed approach unless there
are objections.
