Re: [PATCH] eal: provide rte attribute macro for GCC attribute

[Thomas Monjalon <thomas@monjalon.net>]

18/02/2024 15:51, Mattias Rönnblom:
> On 2024-02-18 13:24, Thomas Monjalon wrote:
> > 15/02/2024 23:20, Tyler Retzlaff:
> >> Provide a new macro __rte_attribute(a) that when directly used
> >> compiles to empty for MSVC and to __attribute__(a) when using GCC/LLVM.
> >>
> >> Replace direct use of __attribute__ in __rte_xxx macros where there is
> >> existing empty expansion of the macro for MSVC allowing removal of
> >> repeated #ifdef RTE_TOOLCHAIN_MSVC per macro to expand empty.
> > 
> > I'm not sure it makes sense.
> > I prefer seeing clearly what is empty with MSVC.
> 
> Anything __rte_attribute() is empty on MSVC. You could rename it 
> __rte_attribute_ignored_by_msvc() for clarity.

Yes it would bring more clarity.
But I still prefer #ifdef which may work with more compilers.

> One could note that on the ignore list are things like "may_alias" and 
> "packed", so whatever comes out of a MSVC build should not be expected 
> to actually work.
> 
> Unless I'm missing something, for all the attributes that will have 
> MSVC-propriety equivalent, the usage pattern would have to change, since 
> the syntax is different in incompatible ways.
> 
> Wouldn't it be better to ask the MSVC team to add support GCC 
> attributes? ICC and LLVM managed, so why not Microsoft. Then you would 
> solve this issue for all Open Source projects, not only DPDK.

We can expect MSVC to improve.
That's another reason why I prefer to keep #ifdef to keep track easily.