diff options
Diffstat (limited to 'subx/057write.subx')
| -rw-r--r-- | subx/057write.subx | 165 |
1 files changed, 165 insertions, 0 deletions
diff --git a/subx/057write.subx b/subx/057write.subx new file mode 100644 index 00000000..3f2f8a11 --- /dev/null +++ b/subx/057write.subx @@ -0,0 +1,165 @@ +# 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 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 + +# TODO: come up with a way to signal when a write to disk fails +write: # f : fd or (address stream), s : (address array byte) -> <void> + # . 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 5/rm32/EBP . . . . 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 5/rm32/EBP . . . . 0xc/disp8 . # push *(EBP+12) + ff 6/subop/push 1/mod/*+disp8 5/rm32/EBP . . . . 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 + 50/push-EAX + 51/push-ECX + 52/push-EDX + 53/push-EBX + # ECX = f + 8b/copy 1/mod/*+disp8 5/rm32/EBP . . 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 5/rm32/EBP . . . . 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 + 58/pop-to-EAX +$write:end: + # . 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(*_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 |