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 09:30:58AM +0100, Thomas Monjalon wrote:
> 24/03/2021 05:26, Tyler Retzlaff:
> > +#ifndef __cplusplus
> >  #ifndef asm
> >  #define asm __asm__
> >  #endif
> > +#endif
> 
> It requires more explanations.
> Which compilers do not define asm?
> What happens with C++ if asm is undefined?

i guess the subject line on my commit didn't communicate this properly
sorry.

asm is a keyword in both the C and C++ standards. for C++ the keyword is
not permitted to be re-defined.

here is the relevant text from the standard, in particular item (2).

  17.6.4.3.1 Macro names [macro.names]

  1
  A translation unit that includes a standard library header shall not
  #define or #undef names declared in any standard library header.

  2
  A translation unit shall not #define or #undef names lexically identical
  to keywords, to the identifiers listed in Table 3, or to the attribute-tokens
  described in 7.6.

so when including rte_common.h into a translation unit that is being
compiled C++ the rte_common.h violates the standard by leaking the
#define asm macro.

this problem appears as soon as you try to build a C++ based dpdk
application with clang using windows C++ runtime and #include <list>.