JLWalsh / StackVM

A stack-based virtual machine written in C

Stack VM

A VM written in C

In short, Stack VM (SVM for short) is a barebones virtual machine written in C. As the name states, it is a stack-based machine. The machine will features detailed types (i.e not just one type to represent numbers like in JS), native string support, and (hopefully) be lightweight enough to be ported to small embedded devices. As of now, the SVM is capable of operating on primitives such as integers, and more complex types such as strings. It currently has support for memory allocation operations, but they might be removed in favour of a more object-oriented instruction set that would replace OP_ALLOC [size] with something like OP_NEW [objectid].

To get started

In case you want to try it out or contribute to this project, you will need:

• CMake
  • So far, the project has been succesfully compiled with MinGW32 and GCC on Linux
• Clang-format, because C can get messy :)

To build the project solution

mkdir solution
cd solution
cmake ..    

To generate using a specific generator (i.e MinGW Makefiles, Visual Studio solution, etc), see the CMake doc on generators. Or use CMake GUI!

To run tests

After having built the project, from the solution directory:

cd test
ctest --verbose

Types

In a near future, all these types will be part of the VM in some way:

Type	Size	Description
Integer	2	A signed whole number
Unsigned integer	2	A non-signed whole number
Pointer	4	A non-signed whole number capable of representing a memory location
Long	8	A signed whole-number
Unsigned long	8	A non-signed whole number
Float	32	A high-precision number
Byte	1	A group of eight bits
Opcode	2	An opcode used only in the bytecode, alias of unsigned integer

Program structure

StackVM programs can be loaded with constants of any type. Constants will be loaded in a special chunk of heap space that is read-only. Constants are especially useful for things like strings, as we can reference them using pointers, instead of storing them directly in the program. Note that any data between the header and the program is considered to be part of the constants section, and therefore will be loaded into memory. Here is a rough drawing of the program structure:

Required?	Byte offset	Length (in bytes)	Description
Yes	0	8 (ULONG)	File/executable length
Yes	8	4 (ULONG)	Constants length
No	16	Determined by previous entry	Constant values that will be loaded into memory
Yes!	After constants	Determined by executable length - constants length	The program itself!

To build the project

make or make build

Or in debug

make build-debug

To clean the project

make clean