[PATCH v11 0/3] add diagnostics macros to make code portable

[Bruce Richardson]

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 <andremue at linux.microsoft.com> wrote:
> > 
> > > From: Andre Muezerie <andremue at linux.microsoft.com>
> > > To: andremue at linux.microsoft.com
> > > Cc: dev at dpdk.org,  stephen at networkplumber.org
> > > 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?