MACHINE LANGUAGE EXECUTOR

  Run machine code without an object file format.


USAGE

  mlx ADDRESS OFFSET PROGRAM [ARGUMENTS]
  
    The machine language executor maps the contents of a PROGRAM
    file into memory at ADDRESS and calls a function that begins
    at OFFSET. 
  
    If ADDRESS is 0, the kernel will select an address instead.


DEMO 

  An illustration of how to produce a crude implementation of
  the pwd (Print Working Directory) utility for Linux/x86_64.

  $ make
  as -o src/x86_64.o src/x86_64.s
  cc -o bin/mlx src/mlx.c src/x86_64.o -Wall -Werror

  $ cat > /tmp/pwd.ml << EOF
                # Allocate 2048 bytes on the stack.
  48 31 f6              # xor rsi, rsi
  66 be 00 08           # mov si, 2048
  48 29 f4              # sub rsp, rsi

                # getcwd(buffer, 2048)
  48 89 e7              # mov rdi, rsp
  6a 4f                 # push SYS_GETCWD
  58                    # pop rax
  0f 05                 # syscall

                # Get the buffered string length.
  48 31 c0              # xor rax, rax
  48 31 c9              # xor rcx, rcx
  48 ff c9              # dec rcx
  f2 ae                 # repnz scasb
  48 89 ca              # mov rdx, rcx
  48 f7 d2              # not rdx

                # Replace the NUL terminator with NL.
  48 ff cf              # dec rdi
  b0 0a                 # mov al, '\n'
  88 07                 # mov [rdi], al

                # write(STDOUT_FILENO, buffer, strlen(buffer))
  48 89 e6              # mov rsi, rsp
  6a 01                 # push STDOUT_FILENO
  5f                    # pop rdi
  6a 01                 # push SYS_WRITE
  58                    # pop rax
  0f 05                 # syscall

                # Deallocate the buffer.
  66 81 c4 00 08        # add sp, 2048

                # Return EXIT_SUCCESS.
  48 31 c0              # xor rax, rax
  c3                    # ret
EOF


  $ misc/encode < /tmp/pwd.ml > /tmp/pwd

  $ xxd /tmp/pwd
  00000000: 4831 f666 be00 0848 29f4 4889 e76a 4f58  H1.f...H).H..jOX
  00000010: 0f05 4831 c048 31c9 48ff c9f2 ae48 89ca  ..H1.H1.H....H..
  00000020: 48f7 d248 ffcf b00a 8807 4889 e66a 015f  H..H......H..j._
  00000030: 6a01 580f 0566 81c4 0008 4831 c0c3       j.X..f....H1..

  $ bin/mlx 0 0 /tmp/pwd
  /home/user/src/mlx

  $ echo $?
  0


AUTHOR

  Justin Swartz <justin.swartz@risingedge.co.za>