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## read a character from stdin, save it to a local on the stack, write it to stdout
#
# To run:
# $ subx translate ex5.subx ex5
# $ subx run ex5
== 0x08048054 # code segment, after leaving room for ELF header and segment headers
# 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
## function main
# prolog
55/push # push EBP
89/copy 3/mod/direct 5/rm32/EBP 4/r32/ESP # copy ESP to EBP
# allocate x on the stack
81 5/subop/subtract 3/mod/direct 4/rm32/ESP 4/imm32 # subtract 4 bytes from ESP
## read(stdin, x, 1)
# fd = 0 (stdin)
bb/copy 0/imm32 # copy 0 to EBX
# initialize x (location to write result to)
89/copy 3/mod/direct 1/rm32/ECX 5/r32/EBP # copy EBP to ECX
# size = 1 character
ba/copy 1/imm32 # copy 1 to EDX
# read(fd, x, size)
b8/copy 3/imm32 # copy 3 to EAX
cd/syscall 0x80/imm8 # int 80h
## write(stdout, x, 1)
# fd = 1 (stdout)
bb/copy 1/imm32 # copy 1 to EBX
# initialize x (location to read from)
89/copy 3/mod/direct 1/rm32/ECX 5/r32/EBP # copy EBP to ECX
# size = 1 character
ba/copy 1/imm32 # copy 1 to EDX
# write(fd, x, size)
b8/copy 4/imm32 # copy 4 to EAX
cd/syscall 0x80/imm8 # int 80h
## exit(EBX)
b8/copy 1/imm32 # copy 1 to EAX
cd/syscall 0x80/imm8 # int 80h
# vim:ft=subx:nowrap
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