subx/examples/ex4.subx


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## read a character from stdin, save it to a global, write it to stdout
#
# To run (from the subx directory):
#   $ subx translate examples/ex4.subx -o examples/ex4
#   $ subx run examples/ex4

== code

# syscall(read, stdin, X, 1)
    # fd = 0 (stdin)
bb/copy-to-EBX  0/imm32
    # initialize X (location to write result to)
b9/copy-to-ECX  X/imm32
    # size = 1 character
ba/copy-to-EDX  1/imm32
    # syscall
b8/copy-to-EAX  3/imm32/read
cd/syscall  0x80/imm8

# syscall(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
b8/copy-to-EAX  4/imm32/write
cd/syscall  0x80/imm8

# syscall(exit, EBX)
b8/copy-to-EAX  1/imm32/exit
cd/syscall  0x80/imm8

== data

X:
    00 00 00 00  # space for read() to write to

# . . vim:nowrap:textwidth=0