Re: [RFC/RFA] gdb extension for Harvard architectures

[Jim Blandy <jimb@zwingli.cygnus.com>]

Andrew Cagney <ac131313@cygnus.com> writes:
> >  - If an expression E has some type T, then &E has type T *.
> 
> To be pedantic:
> 
> 	An expression E has some type T, then &E has type T *@data.
> 
> It is defining a pointer from data space to either code or data
> space.

If something isn't an lvalue, the space qualifier is meaningless.

> > This is a fundamental operation, and choosing the wrong behavior here
> > will inevitably cause troubles elsewhere, too.
> > 
> > Suppose you attach the qualifier to the pointer, and not the pointee.
> > That is, `@code' may only be applied to pointer types, and it means
> > that the pointer points to something in code space.
> 
> Sorry, you've lost me.  What is being discussed is the cast operator and 
> its semantics. A cast takes a type and expression parameter and returns 
> an expression.

That was meant to answer the following question you asked:

> The basic framework attached the segment information to the pointee 
> rather than pointer.  Was this an arbitrary decision or based on some 
> theoretical framework.



> To the best of my knowledge, ISO C says nothing about cast operations 
> that convert between code and data pointers.  What we do have is a 
> certain level of accepted behavour.  For instance on a unified byte 
> addressable address space architecture things like:
> 
> 	sizeof(void*) == sizeof((*)())
> 	((*)()) (void*) foo == ((*)()) foo
> 
> However, on a harvard address space architecture we have none of that.

Right.  We don't.  What's your point?