mmastrac/bootstrap

Bootstrapping VM for bare metal to trusted C compilation

bootstrap's Issues

Avoid hard-coded length for label parser in bootstrap2

bootstrap2 assumes that all labels in bootstrap3 are 8 characters long. This makes for a lot of unnecessary underscores in bootstrap3.

This is probably not a complex bit of work, but #2 might make this easier.

Reduce use of hardcoded addresses in bootstrap2

bootstrap2 hardcodes a whole bunch of addresses, and uses a bunch of registers for others. Most (if not all) of these address could be pushed into the jump table at the start of the program (or alternatively, create an aux address table) to make this program easier to modify.

bootstrap3's %call should use stack to stage args

As return values and arguments share the same register (r0), attempting to make a call to another function where the return value is in another position other than the first one causes that argument to get corrupted.

For example:

%call function @foo, @ret will first clobber @ret (aka r0) with @foo, then attempt to put the clobbered value of r0 into r1.

Instead, %call should push the arguments to the stack and then pop them into registers. This is far less efficient, but we're not worried about efficiency in this stage.

This could potentially simplify some argument handling in bootstrap4/compiler0 as well.

Implement %tcall in bootstrap3

Having a tail call macro in bootstrap3 would simplify a lot of code. This code would need to adjust the stack pointer like %ret does before making the call to the procedure.

Create calling convention for bootstrap3

bootstrap3 currently uses an ad-hoc calling convention. After #1 is implemented we could create macros for a function prefix/suffix that would allow us to automatically save and restore a set of registers to the stack on function entry/exit.

There is currently a calling convention in bootstrap4 but that might be too much and too complex for this particular stage. It might be best to just always assume that there are 8 parameters to every function and create the prefix and suffix with that assumption.

This is a pretty big chunk of work as it requires refactoring almost every function in this file.

Make the macros hardcoded in bootstrap2 dynamic

These macros could be hoisted out of bootstrap2 and defined ad-hoc by bootstrap3. This is a good first issue to work on.

file not being created, invalid opcode

when I run it I get this

$ sh ./bootstrap/make.sh 
open: No such file or directory
Invalid opcode

I tried changing this line

//		int r = open((const char*)&program[arg1], arg2, 0777);
		int r = open((const char*)&program[arg1], arg2|O_RDWR|O_CREAT, 0777);

and this happens

$ sh ./bootstrap/make.sh 
Invalid opcode
Invalid opcode