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ChaiVM - Virtual machine for chai bytecode.

You can read more about chai isa here

How to build:

$ make build

How to use

$ build/chai <app.chai>

Chai bytecode currently is just a Sequence of instructions.

For instance, there is disassembler of simple app.chai

fn main 8 0 {
  Ldia 6
  Star r2
  Ldia 8
  Star r3
  Ldra r3
  Mul r2
  Printc acc
  Mov 0 r0
  Ret
}

Where Ret returns exit code r0. "main" is name of the starting function, 8 is number of registers in it, 0 is number of arguments passing into the function. This script compiled to chai-bytecode should print "0", because '0' == 48.

Chai file format

Except for classes, our file format is similar to jvm ClassFile Structure. Its content is the following:

  • Constants count (imm)
  • Constant[]
  • klass_info count (imm)
  • klass_info[]
  • func_info count (imm)
  • func_info[]

Where imm is 2 bytes.

Constant has a 1 byte tag that specifies its type(ConstI64, or ConstFuncNameAndType and so on) and the payload then.

klass_info structure:

klass_info {
  imm ConstRawStr              // Klass name index in constant pool
  u1 nFields                   // Count of fields
  field_info[]                 // field_infos array
}

field_info {
  imm ConstRawStr              // Field name index in constant pool
  u1 type                      // 0 if primitive, some class otherwise
  union {
    u1 tag                     // (first byte 0, second determines) 1 for i64, 2 for f64
    imm klassNum               // Klass number, counting only klasses from top to bottom
  }
}

func_info structure:

func_info {
  imm accessFlagsCount
  imm ConstFuncNameAndType
  imm attsCount                // Count of attributes. Now only Code attribute exists
  imm attNameIndex             // Id of attribute, Now can be arbitrary
  imm attLen                   // Size of the Code atribute in bytes 
  u1 maxRegisters              // Number of registers used in function
  u1 nargs                     // Number of arguments to pass
  u4 codeLen                   // Size of code(instructions only) in bytes
  u1[] code                    // Instructions, byte array.
}

Strings

All strings are contained in CodeManager.stringPool_. Some of them initialized with starting of VM but you also can create own string in runtime via StringConcat or StringSlice instructions.