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## read a character from stdin, save it to a global, write it to stdout
#
# To run:
# $ subx translate ex4.subx ex4
# $ subx run ex4
== 0x08048074 # code segment, after leaving room for ELF header and segment headers
# opcode ModR/M SIB displacement immediate
# instruction mod, reg, Reg/Mem bits scale, index, base
# 1-3 bytes 0/1 byte 0/1 byte 0/1/2/4 bytes 0/1/2/4 bytes
## read(stdin, x, 1)
# fd = 0 (stdin)
bb 0/imm32 # copy 0 to EBX
# set location to write to
b9 a7 90 04 08 # copy 0x080490a7 to ECX
# size = 1 character
ba 1/imm32 # copy 1 to EDX
# syscall = read
b8 3/imm32 # copy 3 to EAX
# call
cd 128/imm8 # int 80h
## write(stdout, x, 1)
# fd = 1 (stdout)
bb 1/imm32 # copy 1 to EBX
# set location to write to
b9 a7 90 04 08 # copy 0x080490a7 to ECX
# size = 1 character
ba 1/imm32 # copy 1 to EDX
# syscall = write
b8 4/imm32 # copy 3 to EAX
# call
cd 128/imm8 # int 80h
## exit(EBX)
b8 1/imm32 # copy 1 to EAX
cd 128/imm8 # int 80h
== 0x080490a7
00 00 00 00 # space for read() to write to
# vim:ft=subx:nowrap
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