Hello! Sorry if I appear to be posting a lot of questions (if you
saw my LLVM one, thanks again for the help) I'm trying to throw
some things together and learn a lot.
So I've been researching compilers and virtual machines recently,
I've managed to implement some fairly good front ends and the
past few weeks I've been looking into various options for back
ends. Something that really interests me in virtual machine type
systems.
I looked into things like the JVM and Google's V8 JavaScript
engine and read that they directly execute native code--reason
for their speed (at least V8).
So I did some research and found tons of code snippets and stuff
for C/C++ (of course) but from that I managed to write this in D:
import std.stdio, core.memory;
void main()
{
uint* opcodes = cast(uint*)GC.malloc(2);
opcodes[0] = 0xCC;
/* System call of some sort */
/* Function pointer */
void* delegate() func;
func.ptr = cast(void*)opcodes;
/* Call function */
func();
GC.free(opcodes);
}
This reserves some memory and places some CPU instructions, makes
a function pointer to that block of memory, calls it, and frees
the memory. The only problem is, is that most processors and OS's
block direct memory execution like this, to my understanding
there is some way to mark this block of memory executable. (Cause
without doing so there is a segmentation fault) I've seen ways to
do this in Linux and Windows in C/C++ but I have no clue where to
start with this in D. If anyone has any ideas for at least Linux
that would be great, thanks a lot everyone!
