## example showing file syscalls # Create a file, open it for writing, write a character to it, close it, open # it for reading, read a character from it, close it, delete it, and return # the character read. # # To run: # $ subx translate ex8.subx ex8 # $ subx run ex8 # Expected result: # $ echo $? # 97 == code # 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 ## creat(filename) bb/copy . . . . . . . filename/imm32 # copy to EBX b9/copy . . . . . . . 0x180/imm32/fixed-perms # copy to ECX b8/copy . . . . . . . 8/imm32/creat # copy 8 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h ## stream = open(filename, O_WRONLY, 0) # we can't use 'fd' because it looks like a hex byte bb/copy . . . . . . . filename/imm32 # copy to EBX b9/copy . . . . . . . 1/imm32/wronly # copy 1 to ECX ba/copy . . . . . . . 0x180/imm32/fixed-perms # copy 0 to EDX b8/copy . . . . . . . 5/imm32/open # copy 5 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h # save stream bb/copy . . . . . . . stream/imm32 # copy to EBX 89/copy 0/mod/indirect 3/rm32/EBX 0/r32/EAX # copy EAX to *EBX ## write(stream, "a", 1) # load stream bb/copy . . . . . . . stream/imm32 # copy to EBX 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX # b9/copy . . . . . . . a/imm32 # copy to ECX ba/copy . . . . . . . 1/imm32/size # copy 1 to EDX b8/copy . . . . . . . 4/imm32/write # copy 4 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h ## close(stream) # load stream bb/copy . . . . . . . stream/imm32 # copy to EBX 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX # b8/copy . . . . . . . 6/imm32/close # copy 6 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h ## stream = open(filename, O_RDONLY, 0) bb/copy . . . . . . . filename/imm32 # copy to EBX b9/copy . . . . . . . 0/imm32/rdonly # copy 0 to ECX ba/copy . . . . . . . 0x180/imm32/fixed-perms # copy to EDX b8/copy . . . . . . . 5/imm32/open # copy 5 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h # save stream bb/copy . . . . . . . stream/imm32 # copy to EBX 89/copy 0/mod/indirect 3/rm32/EBX 0/r32/EAX # copy EAX to *EBX ## read(stream, b, 1) # load stream bb/copy . . . . . . . stream/imm32 # copy to EBX 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX # b9/copy . . . . . . . b/imm32 # copy to ECX ba/copy . . . . . . . 1/imm32/size # copy 1 to EDX b8/copy . . . . . . . 3/imm32/read # copy 3 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h ## close(stream) # load stream bb/copy . . . . . . . stream/imm32 # copy to EBX 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX # b8/copy . . . . . . . 6/imm32/close # copy 6 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h ## unlink(filename) bb/copy . . . . . . . filename/imm32 # copy to EBX b8/copy . . . . . . . 0xa/imm32/unlink # copy 10 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h ## exit(b) # load b bb/copy . . . . . . . b/imm32 # copy to EBX 8b/copy 0/mod/indirect 3/rm32/EBX 3/r32/EBX # copy *EBX to EBX # b8/copy . . . . . . . 1/imm32/exit # copy 1 to EAX cd/syscall . . . . . . . 0x80/imm8 # int 80h == data stream: 00 00 00 00 a: 61 00 00 00 b: 00 00 00 00 filename: 2e 66 6f 6f 00 00 00 00 # vim:ft=subx:nowrap:tw&