Re: svn commit: r322875 - head/sys/dev/nvme

> Author: imp
> Date: Fri Aug 25 04:33:06 2017
> New Revision: 322875
> URL: 
> https://svnweb.freebsd.org/changeset/base/322875
> 
> 
> Log:
>   Use _Static_assert
>   
>   These files are compiled in userland too, so we can't use sys/systm.h
>   and rely on CTASSERT. Switch to using _Static_assert instead.
>   
>   MFC After: 3 days
>   Sponsored by: Netflix
> 
> Modified:
>   head/sys/dev/nvme/nvme.h
>   head/sys/dev/nvme/nvme_util.c

As I remember _Static_assert is from C11, not
the older C99.

As I understand head/sys/dev/nvme/nvme.h use by
C++ code could now reject attempts to use
_Static_assert .

There have been at least one old bugzilla report
for such. An example is 205453 (back around
2015-Dec).

From back then:

> # more main.cc
> #include "/usr/include/sys/cdefs.h"
> _Static_assert(1,"Test");
> int main(void)
> {
>     return 0;
> }
> 
> For example:
> 
> # g++49 main.cc
> main.cc:2:15: error: expected constructor, destructor, or type conversion before '(' token
>  _Static_assert(1,"Test");
> . . .
> g++49, g++5, and powerpc64-portbld-freebsd11.0-g++ all reject the above source the same way that libcxxrt/guard.cc compiles are rejected during powerpc64-portbld-freebsd11.0-g++ based buildworld lib32 -m32 compiles. 
> 
> gcc49, gcc5, and powerpc64-portbld-freebsd11.0-gcc all accept the above instead (when in main.c instead of main.cc so it is handle as C code), with or without the include. _Static_assert is specific to C11 and is not part of C++. It takes explicit definitions to make the syntax acceptable as C++.
> 
> Note: clang++ (3.7) accepts the use of the C11 _Static_assert, with or without the include, going well outside the C++ language definition.
> 
> . . .
> 
> Fixed in r297299 .

(The context was a C++ file head/contrib/libcxxrt/guard.cc so C++'s
static_assert was used instead and -std=c++11 was added for the
library in question [libcxxrt].)

Unless head/sys/dev/nvme/nvme.h is not to be used from
C++ code: use of _Static_assert in the header would appear
to be a problem.

===
Mark Millard
markmi at dsl-only.net