Re: C's trikery semantic opens up backdoor in new Linux kernel

[Hyman Rosen <hyrosen@mail.com>]

Dave Thompson wrote:
 > you can accomplish the same thing by writing out (desired declarations etc.
> from) the contents of the include-d file changed as specified.

Note that a Standard C++ compiler is not required to represent
such a modified structure in the same way as the original. If
the class name for the modified class is the same as the original,
and the program includes both, the behavior is undefined. If you
attempt to examine an object of the original type using a pointer
to the new type, the behavior is undefined.

In Standard C++, the technical meaning of "undefined behavior" is
that if an operation with undefined behavior is ever encountered
by a program, the behavior of the entire program is completely
unspecifed by the standard, even for things that happen before
that operation. Violating the One-Definition Rule (that is, the
definition of a type or function must be exactly the same throughout
an entire program, when the language permits a definition to appear
more than once) makes a program undefined as well.