backend: basic x86_64 assembly codegen for some global vars

[ehaas]

Some basic assembly codegen, tested with:

/* main.c */
int printf(const char *fmt, ...);
extern char foo[];
extern int bar;
extern double baz;

int main(void)
{
    printf("%s\n%d\n%lf\n", foo, bar, baz);
    return 0;
}

/* test.c */
char foo[] = "hello";
int bar = 42;
double baz = 3.14;

~$ gcc -c main.c
~$ arocc -O0 test.c main.o`
~$ ./a.out
hello
42
3.140000

I structured things the way I did so that aro (the frontend module) wouldn't depend on this assembly backend (as in, needing to import it so that it can call it from Driver). The way things are set up now, a do-nothing function can be passed as the final argument of Driver.main. But I'm not sure if that's the best way to achieve that.

My next goal is to get very basic function generation going and then I can revive the EXPECTED_OUTPUT tests.

[Vexu]

I structured things the way I did so that aro (the frontend module) wouldn't depend on this assembly backend (as in, needing to import it so that it can call it from Driver). The way things are set up now, a do-nothing function can be passed as the final argument of Driver.main. But I'm not sure if that's the best way to achieve that.

I'd be OK with placing the genAsm function in backend.zig and the Driver calling it from there unless you want to do it like this.

[ehaas]

I'd be OK with placing the genAsm function in backend.zig and the Driver calling it from there unless you want to do it like this.

It looks like backend currently does not depend on frontend so I was trying to preserve that property - is it worth keeping it that way?

[ehaas]

I changed things around a bit to use an optional function instead of anytype, and just have codegen return FatalError for unimplemented things instead of a new kind of error.

[Vexu]

It looks like backend currently does not depend on frontend so I was trying to preserve that property - is it worth keeping it that way?

The backend should be kept separate, I didn't notice this used Compilation for all the type details. I guess this could also be moved to the main module since it's not standalone like the backend module is.

Either way feel free to merge as is.