path: root/linux/ex4.subx

# Read a character from stdin, save it to a global, write it to stdout.
#
# To run:
#   $ bootstrap/bootstrap translate ex4.subx -o ex4
#   $ bootstrap/bootstrap run ex4

== data

# the global variable we save to
X:
    0/imm32  # space for read() to write to

== code

Entry:
# read(stdin, X, 1)
# . fd = 0 (stdin)
bb/copy-to-ebx  0/imm32
# . data = X (location to write result to)
b9/copy-to-ecx  X/imm32
# . size = 1 character
ba/copy-to-edx  1/imm32
# . syscall
e8/call  syscall_read/disp32

# write(stdout, X, 1)
# . fd = 1 (stdout)
bb/copy-to-ebx  1/imm32
# . initialize X (location to read from)
b9/copy-to-ecx  X/imm32
# . size = 1 character
ba/copy-to-edx  1/imm32
# . syscall
e8/call  syscall_write/disp32

# exit(ebx)
e8/call  syscall_exit/disp32

# . . vim:nowrap:textwidth=0