Re: Is void* compatible with function pointers?

[deadalnix via Digitalmars-d]

On Tuesday, 24 June 2014 at 01:41:13 UTC, Steven Schveighoffer 
wrote:
This is because most CPUs consider the instructions as 
immutable.
Even x86 do not provide any guarantee (which makes it very hard
to swap implementation outside of a VM).

Remember, these are not functions, but function pointers. You 
are not modifying the function at all.


void* is not a function and can come from anything that is 
mutable.

Casting from void* to function is pretty guaranteed to be
undefined behavior on all plateforms, unless you emit the 
proper
barriers.

Can you demonstrate a C example that will fail on ARM?

Anything that JIT is affected. Consider the pseudocode:

void JIT() {
    void* code = malloc(XXX);
    // Write instructions into the allocated chunk of memory.

    membar(); // Memory barrier to avoid reordering.

    auto fun = cast(void function()) code;
    fun(); // Even if your codegen is correct, anything can 
happen this point.
}