# write-byte: write a single byte to a buffered-file. The write may be buffered. # flush: write out any buffered writes to disk. # # TODO: Come up with a way to signal failure to write to disk. This is hard # since the failure may impact previous calls that were buffered. == data # The buffered file for standard output. Stdout: # file descriptor or (address stream) 01 00 00 00 # 1 = standard output # current write index 00 00 00 00 # current read index 00 00 00 00 # length (8) 08 00 00 00 # data 00 00 00 00 00 00 00 00 # 8 bytes # TODO: 8 bytes is too small. We'll need to grow the buffer for efficiency. But # I don't want to type in 1024 bytes here. == code # instruction effective address register 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 # main: e8/call run-tests/disp32 # 'run-tests' is a function created automatically by SubX. It calls all functions that start with 'test-'. # syscall(exit, Num-test-failures) 8b/copy 0/mod/indirect 5/rm32/.disp32 . . 3/r32/EBX Num-test-failures/disp32 # copy *Num-test-failures to EBX b8/copy-to-EAX 1/imm32/exit cd/syscall 0x80/imm8 # Write lower byte of 'n' to 'f'. write-byte: # f : (address buffered-file), n : num -> # . prolog 55/push-EBP 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP # . save registers 51/push-ECX 57/push-EDI # EDI = f 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 7/r32/EDI 8/disp8 . # copy *(EBP+8) to EDI # ECX = f->write 8b/copy 1/mod/*+disp8 7/rm32/EDI . . . 1/r32/ECX 4/disp8 . # copy *(EDI+4) to ECX # if (f->write >= f->length) flush and clear f's stream 3b/compare 1/mod/*+disp8 7/rm32/EDI . . . 1/r32/ECX 0xc/disp8 . # compare ECX with *(EDI+12) 7c/jump-if-lesser $write-byte:to-stream/disp8 # . flush(f) # . . push args 57/push-EDI # . . call e8/call flush/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # . clear-stream(stream = f+4) # . . push args 8d/copy-address 1/mod/*+disp8 7/rm32/EDI . . . 0/r32/EAX 4/disp8 . # copy EDI+4 to EAX 50/push-EAX # . . call e8/call clear-stream/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP $write-byte:to-stream: # write to stream # f->data[f->read] = LSB(n) 31/xor 3/mod/direct 0/rm32/EAX . . . 0/r32/EAX . . # clear EAX 8a/copy-byte 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 0/r32/AL 0xc/disp8 . # copy byte at *(EBP+12) to AL 88/copy-byte 1/mod/*+disp8 4/rm32/sib 7/base/EDI 1/index/ECX . 0/r32/AL 0x10/disp8 . # copy AL to *(EDI+ECX+16) # ++f->read ff 0/subop/increment 1/mod/*+disp8 7/rm32/EDI . . . . 4/disp8 . # increment *(EDI+4) $write-byte:end: # . restore registers 5f/pop-to-EDI 59/pop-to-ECX # . epilog 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP 5d/pop-to-EBP c3/return flush: # f : (address buffered-file) -> # . prolog 55/push-EBP 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP # . save registers 50/push-EAX 51/push-ECX # EAX = f 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . 0/r32/EAX 8/disp8 . # copy *(EBP+8) to EAX # write-stream(f->fd, data = f+4) # . . push args 8d/copy-address 1/mod/*+disp8 0/rm32/EAX . . . 1/r32/ECX 4/disp8 . # copy EAX+4 to ECX 51/push-ECX ff 6/subop/push 0/mod/indirect 0/rm32/EAX . . . . . . # push *EAX # . . call e8/call write-stream/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP $flush:end: # . restore registers 59/pop-to-ECX 58/pop-to-EAX # . epilog 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP 5d/pop-to-EBP c3/return # - tests test-write-byte-single: # - check that read-byte returns first byte of 'file' # setup # . clear-stream(_test-stream) # . . push args 68/push _test-stream/imm32 # . . call e8/call clear-stream/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # . clear-stream(_test-buffered-file+4) # . . push args b8/copy-to-EAX _test-buffered-file/imm32 05/add-to-EAX 4/imm32 50/push-EAX # . . call e8/call clear-stream/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # write-byte(_test-buffered-file, 'A') # . . push args 68/push 0x41/imm32 68/push _test-buffered-file/imm32 # . . call e8/call write-byte/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # flush(_test-buffered-file) # . . push args 68/push _test-buffered-file/imm32 # . . call e8/call flush/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 4/imm32 # add to ESP # check-ints-equal(*_test-stream->data, 'A', msg) # . . push args 68/push "F - test-write-byte-single"/imm32 68/push 0x41/imm32 # . . push *_test-stream->data b8/copy-to-EAX _test-stream/imm32 ff 6/subop/push 1/mod/*+disp8 0/rm32/EAX . . . . 0xc/disp8 . # push *(EAX+12) # . . call e8/call check-ints-equal/disp32 # . . discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP # . end c3/return # . . vim:nowrap:textwidth=0