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## read a character from stdin, save it to a global, write it to stdout
#
# To run:
# $ subx translate ex4.subx -o ex4
# $ subx run ex4
== code
# instruction effective address operand displacement immediate
# op subop mod rm32 base index scale r32
# 1-3 bytes 3 bits 2 bits 3 bits 3 bits 3 bits 2 bits 2 bits 0/1/2/4 bytes 0/1/2/4 bytes
# read(stdin, x, 1)
# fd = 0 (stdin)
bb/copy 0/imm32 # copy 0 to EBX
# initialize x (location to write result to)
b9/copy x/imm32 # copy to ECX
# size = 1 character
ba/copy 1/imm32 # copy 1 to EDX
# read(fd, x, size)
b8/copy 3/imm32/read # copy 3 to EAX
cd/syscall 0x80/imm8
# write(stdout, x, 1)
# fd = 1 (stdout)
bb/copy 1/imm32 # copy 1 to EBX
# initialize x (location to read from)
b9/copy x/imm32 # copy to ECX
# size = 1 character
ba/copy 1/imm32 # copy 1 to EDX
# write(fd, x, size)
b8/copy 4/imm32/write # copy 4 to EAX
cd/syscall 0x80/imm8
# exit(EBX)
b8/copy 1/imm32/exit # copy 1 to EAX
cd/syscall 0x80/imm8
== data
x:
00 00 00 00 # space for read() to write to
# vim:ft=subx:nowrap
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