1 ## read a character from stdin, save it to a global, write it to stdout 2 # 3 # To run: 4 # $ subx translate ex4.subx ex4 5 # $ subx run ex4 6 7 == 0x08048074 # code segment, after leaving room for ELF header and segment headers 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 ## read(stdin, x, 1) 13 # fd = 0 (stdin) 14 bb/copy 0/imm32 # copy 0 to EBX 15 # initialize x (location to write result to) 16 b9/copy 0x080490a7/imm32 # copy to ECX 17 # size = 1 character 18 ba/copy 1/imm32 # copy 1 to EDX 19 # read(fd, x, size) 20 b8/copy 3/imm32 # copy 3 to EAX 21 cd/syscall 0x80/imm8 # int 80h 22 23 ## write(stdout, x, 1) 24 # fd = 1 (stdout) 25 bb/copy 1/imm32 # copy 1 to EBX 26 # initialize x (location to read from) 27 b9/copy 0x080490a7/imm32 # copy to ECX 28 # size = 1 character 29 ba/copy 1/imm32 # copy 1 to EDX 30 # write(fd, x, size) 31 b8/copy 4/imm32 # copy 4 to EAX 32 cd/syscall 0x80/imm8 # int 80h 33 34 ## exit(EBX) 35 b8/copy 1/imm32 # copy 1 to EAX 36 cd/syscall 0x80/imm8 # int 80h 37 38 == 0x080490a7 39 00 00 00 00 # space for read() to write to 40 41 # vim:ft=subx:nowrap