full-stack-hello

full-stack-hello is a minimal virtual machine kit capable of performing tasks at any level of the technical stack on which a typical 'Hello World' program execution depends. It means:

• Instruction Set Architecture (ISA);
• Virtual machine implementing the ISA;
• Assembly and/or Compiler following the ISA;
• Runtime support such as standard libraries and ELF;

Instruction set

Opcode	Description
OP_ADD	sum two operands
OP_SUB	subtract two operands
OP_MUL	multiply two operands
OP_DIV	divide two two operands
OP_MOD	Modulo, remainder of operand 1 divided by operand 2
OP_PRINT	print integer or string
OP_JLT	jump to specified address (in operand 2) if operand 1 is less than 0
OP_JLE	jump to specified address (in operand 2) if operand 1 is less than or equal to 0
OP_JZ	jump to specified address (in operand 2) if operand 1 is equal to 0
OP_JGE	jump to specified address (in operand 2) if operand 1 is greater than or equal to 0
OP_JGT	jump to specified address (in operand 2) if operand 1 is greater than 0
OP_JNZ	jump to specified address (in operand 2) if operand 1 is not equal to 0
OP_JMP	jump to specified address
OP_CALL	call to specified address
OP_RET	return to where called from
OP_HALT	terminate VM

Assembly Notation

• Registers are specified by # as temporary storage.
  • print #1 dumps the content of register #1.
• An immediate value (or simply an immediate or imm) is a piece of data that is stored as part of the instruction itself instead of being in a memory location or a register.
  • mul $-2 $2 #4 stores the result of (-2) * (2) into register #4.
• A valid Label name ends with : and is referred as :X in any JMP/CALL instructions to jump to label X.

  A:
  print $1
  jmp :A
  

  • Infinite loop that dumps constant 1.

Build and Verify

$ make
cc -Wall -std=gnu99 -g -c -o vm.o -MMD -MF .vm.o.d vm.c
cc -Wall -std=gnu99 -g -c -o as.o -MMD -MF .as.o.d as.c
cc -Wall -std=gnu99 -g -c -o driver.o -MMD -MF .driver.o.d driver.c
cc -Wall -std=gnu99 -g -o as_exec vm.o as.o driver.o
$ make check
42
tests/halt.s pass

Hello World
tests/hello.s pass

42
50
150
tests/test.s pass

$ make test
python tests/run_tests.py
..
----------------------------------------------------------------------
Ran 4 tests in 0.002s

OK

Assembler Usage

Specify -h to obtain the description of the assembler.

$ ./as_exec -h
Usage: as_exec [-w] [-x] [-o <out_file>] <in_file>
       -w Assemble <in_file> and write to an ELF file, see -o below
       -o if -w is specifed, <out_file> is used to store the object code
       -x Load <in_file> and execute it

       <in_file> the file name to be used by commands above

For example, if the assembly file in concern is tests/coverage.s

1. Assemble an assembly source file and evaluate (execute) it.

   ./as_exec tests/hello.s
   

2. Assemble an assembly source file and write to default ELF file tests/hello.o.

   ./as_exec -w tests/hello.s
   

3. Assemble an assembly source file and write to default ELF file tests/temp.o.

   ./as_exec -o tests/temp.o -w tests/hello.s
   

4. Laod an assembled ELF file tests/hello.o and evaluate (rexcute) it.

   ./as_exec -x tests/hello.o
   

The common ELF tools, such as objdump, can be applied to the output ELF file.

objdump -x tests/hello.o

Currently, the ELF support is very limited and could be improved.

Licensing

full-stack-hello is freely redistributable under the two-clause BSD License. Use of this source code is governed by a BSD-style license that can be found in the LICENSE file.