Re: [dpdk-dev] [PATCH] eal: standard c++ forbids defining the keyword asm as a macro

[Tyler Retzlaff <roretzla@linux.microsoft.com>]

On Wed, Mar 24, 2021 at 06:52:40PM +0100, Thomas Monjalon wrote:
> 24/03/2021 18:28, Tyler Retzlaff:
> > 
> > so to qualify. you mean maybe it is breaking compilation of c++ in a
> > compiler that explicitly violates c++ standard when compiling c++? that
> > would mean it is not a c++ compiler.
> 
> The asm keyword is part of all C++ standards?
> It seems asm is non-standard in C,
> that's why we use __asm__.

the keyword is standard the meaning of the keyword is implementation
defined for both C and C++. though the C11 standard describes a
"common implementation is via statement of the form ..." [J.5.10]

> > in general i don't think it is a good practice to have dpdk introduce
> > names into the application namespace unqualified, but the point you make
> > is valid it can break c++ compilation if something was using this macro
> > as a convenience to the compiler specific extension __asm__. there will
> > be further issues with varying syntaxes that __asm__-style extensions
> > take from compiler to compiler as well.
> 
> Yes we need to make sure there is no specific extension involved.
> Is C++ asm the same as the C __asm__?

i don't think I can answer that as it depends on the compiler. there may
be no implementation at all or different implementations for asm or __asm__.
so basically neither form is portable (for an arch). though for __asm__
probably there is de-facto standardization around what gcc does and clang
mimics.

> > would you prefer that i change the preprocessor protection to include only
> > windows? since i'm certain that this will break for any c++ compiler on
> > windows the moment any stl header is included.
> 
> No, C++ is probably the right scope.
> 
> I don't know yet. I would like to understand the global picture,
> and have it properly documented in this commit log.

yep, no problem. i suspect we are probably the only ones using c++ and
dpdk (though others can speak up if they do too) which may be why this
has gone unnoticed until now.