1 ## read a character from stdin, save it to a local on the stack, write it to stdout 2 # 3 # To run (from the subx directory): 4 # $ subx translate examples/ex5.subx -o examples/ex5 5 # $ subx run examples/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 # main: 13 # allocate x on the stack 14 81 5/subop/subtract 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # subtract from ESP 15 16 # read(stdin, x, 1) 17 # fd = 0 (stdin) 18 bb/copy . . . . . . . 0/imm32 # copy to EBX 19 # initialize x (location to write result to) 20 8d/copy-address 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 1/r32/ECX 4/disp8 . # copy ESP+4 to ECX 21 # size = 1 character 22 ba/copy . . . . . . . 1/imm32 # copy to EDX 23 # read(fd, x, size) 24 b8/copy . . . . . . . 3/imm32/read # copy to EAX 25 cd/syscall 0x80/imm8 26 27 # write(stdout, x, 1) 28 # fd = 1 (stdout) 29 bb/copy . . . . . . . 1/imm32 # copy to EBX 30 # initialize x (location to read from) 31 8d/copy-address 1/mod/*+disp8 4/rm32/sib 4/base/ESP 4/index/none 1/r32/ECX 4/disp8 . # copy ESP+4 to ECX 32 # size = 1 character 33 ba/copy . . . . . . . 1/imm32 # copy to EDX 34 # write(fd, x, size) 35 b8/copy . . . . . . . 4/imm32/write # copy to EAX 36 cd/syscall 0x80/imm8 37 38 # exit(EBX) 39 b8/copy . . . . . . . 1/imm32/exit # copy to EAX 40 cd/syscall 0x80/imm8 41 42 # vim:ft=subx:nowrap