1 ## read a character from stdin, save it to a local on the stack, write it to stdout 2 # 3 # To run: 4 # $ subx translate ex5.subx ex5 5 # $ subx run ex5 6 7 == code 8 # instruction effective address operand displacement immediate 9 # op subop mod rm32 base index scale r32 10 # 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 11 12 ## function main 13 # prolog 14 55/push # push EBP 15 89/copy 3/mod/direct 5/rm32/EBP 4/r32/ESP # copy ESP to EBP 16 # allocate x on the stack 17 81 5/subop/subtract 3/mod/direct 4/rm32/ESP 4/imm32 # subtract 4 bytes from ESP 18 19 ## read(stdin, x, 1) 20 # fd = 0 (stdin) 21 bb/copy 0/imm32 # copy 0 to EBX 22 # initialize x (location to write result to) 23 89/copy 3/mod/direct 1/rm32/ECX 5/r32/EBP # copy EBP to ECX 24 # size = 1 character 25 ba/copy 1/imm32 # copy 1 to EDX 26 # read(fd, x, size) 27 b8/copy 3/imm32 # copy 3 to EAX 28 cd/syscall 0x80/imm8 # int 80h 29 30 ## write(stdout, x, 1) 31 # fd = 1 (stdout) 32 bb/copy 1/imm32 # copy 1 to EBX 33 # initialize x (location to read from) 34 89/copy 3/mod/direct 1/rm32/ECX 5/r32/EBP # copy EBP to ECX 35 # size = 1 character 36 ba/copy 1/imm32 # copy 1 to EDX 37 # write(fd, x, size) 38 b8/copy 4/imm32 # copy 4 to EAX 39 cd/syscall 0x80/imm8 # int 80h 40 41 ## exit(EBX) 42 b8/copy 1/imm32 # copy 1 to EAX 43 cd/syscall 0x80/imm8 # int 80h 44 45 # vim:ft=subx:nowrap