# write: like _write, but also support in-memory streams in addition to file # descriptors. # # Our first dependency-injected and testable primitive. We can pass it either # a file descriptor or an address to a stream. If a file descriptor is passed # in, we _write to it using the right syscall. If a 'fake file descriptor' or # stream is passed in, we append to the stream. This lets us redirect output # in tests and check it later. # # We assume our data segment will never begin at an address shorter than # 0x08000000, so any smaller arguments are assumed to be real file descriptors. # # A stream looks like this: # read: int # index at which to read next # write: int # index at which writes go # data: (array byte) # prefixed by length as usual == 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 # 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 cd/syscall 0x80/imm8 write: # f : fd or (address stream), s : (address array byte) -> bytes_written/EAX # (If we ever leave the Linux kernel behind, it may be better to return # the number of bytes *not* written. Success would then be signaled by # returning 0.) # prolog 55/push-EBP 89/copy 3/mod/direct 5/rm32/EBP . . . 4/r32/ESP . . # copy ESP to EBP # if (f < 0x08000000) _write(f, s), return # f can't be a user-mode address, so treat it as a kernel file descriptor 81 7/subop/compare 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 8/disp8 0x08000000/imm32 # compare *(EBP+8) 7d/jump-if-greater-or-equal $write:fake/disp8 # push args ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 0xc/disp8 . # push *(EBP+12) ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 8/disp8 . # push *(EBP+8) # call e8/call _write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP eb/jump $write:end/disp8 $write:fake: # otherwise, treat 'f' as a stream to append to # save registers 51/push-ECX 52/push-EDX 53/push-EBX # ECX = f 8b/copy 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none 1/r32/ECX 8/disp8 . # copy *(EBP+8) to ECX # EDX = f.write 8b/copy 0/mod/indirect 1/rm32/ECX . . . 2/r32/EDX . . # copy *ECX to EDX # EBX = f.length 8b/copy 1/mod/*+disp8 1/rm32/ECX . . . 3/r32/EBX 8/disp8 . # copy *(ECX+8) to EBX # EAX = _append-3(&f.data[f.write], &f.data[f.length], s) # push s ff 6/subop/push 1/mod/*+disp8 4/rm32/sib 5/base/EBP 4/index/none . . 0xc/disp8 . # push *(EBP+12) # push &f.data[f.length] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 3/index/EBX . 3/r32/EBX 0xc/disp8 . # copy ECX+EBX+12 to EBX 53/push-EBX # push &f.data[f.write] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 1/base/ECX 2/index/EDX . 3/r32/EBX 0xc/disp8 . # copy ECX+EDX+12 to EBX 53/push-EBX # call e8/call _append-3/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP # f.write += EAX 01/add 0/mod/indirect 1/rm32/ECX . . . 0/r32/EAX . . # add EAX to *ECX # restore registers 5b/pop-to-EBX 5a/pop-to-EDX 59/pop-to-ECX $write:end: # epilog 89/copy 3/mod/direct 4/rm32/ESP . . . 5/r32/EBP . . # copy EBP to ESP 5d/pop-to-EBP c3/return clear-stream: # f : (address stream) -> # 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 # ECX = f.length 8b/copy 1/mod/*+disp8 0/rm32/EAX . . . 1/r32/ECX 8/disp8 . # copy *(EAX+8) to ECX # ECX = &f.data[f.length] 8d/copy-address 1/mod/*+disp8 4/rm32/sib 0/base/EAX 1/index/ECX . 1/r32/ECX 0xc/disp8 . # copy EAX+ECX+12 to ECX # f.write = 0 c7/copy 0/mod/direct 0/rm32/EAX . . . . . 0/imm32 # copy to *EAX # f.read = 0 c7/copy 1/mod/*+disp8 0/rm32/EAX . . . . 4/disp8 0/imm32 # copy to *(EAX+4) # EAX = f.data 81 0/subop/add 3/mod/direct 0/rm32/EAX . . . . . 0xc/imm32 # add to EAX # while (true) $clear-stream:loop: # if EAX >= ECX break 39/compare 3/mod/direct 0/rm32/EAX . . . 1/r32/ECX . . # compare EAX with ECX 7d/jump-if-greater-or-equal $clear-stream:end/disp8 # *EAX = 0 c7/copy 0/mod/direct 0/rm32/EAX . . . . . 0/imm32 # copy to *EAX # EAX += 4 81 0/subop/add 3/mod/direct 0/rm32/EAX . . . . . 4/imm32 # add to EAX eb/jump $clear-stream:loop/disp8 $clear-stream: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 test-write-single: # 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 # write(_test-stream, "Ab") # push args 68/push "Ab"/imm32 68/push _test-stream/imm32 # call e8/call write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # check-ints-equal(EAX, 2) # push args 68/push "F - test-read-single: return EAX"/imm32 68/push 2/imm32 50/push-EAX # call e8/call check-ints-equal/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 0xc/imm32 # add to ESP # check-ints-equal(*_test-stream.data, 41/A 62/b 00 00, msg) # push args 68/push "F - test-write-single"/imm32 68/push 0x006241/imm32/Ab # 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 test-write-appends: # 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 # write(_test-stream, "C") # push args 68/push "C"/imm32 68/push _test-stream/imm32 # call e8/call write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # write(_test-stream, "D") # push args 68/push "D"/imm32 68/push _test-stream/imm32 # call e8/call write/disp32 # discard args 81 0/subop/add 3/mod/direct 4/rm32/ESP . . . . . 8/imm32 # add to ESP # check-ints-equal(*_test-stream.data, 43/C 44/D 00 00, msg) # push args 68/push "F - test-write-appends"/imm32 68/push 0x00004443/imm32/C-D # 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 == data _test-stream: # 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 # vim:nowrap:textwidth=0