diff options
Diffstat (limited to 'linux/108write.subx')
| -rw-r--r-- | linux/108write.subx | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/linux/108write.subx b/linux/108write.subx new file mode 100644 index 00000000..84060c62 --- /dev/null +++ b/linux/108write.subx @@ -0,0 +1,162 @@ +# 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 size 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 + +# TODO: come up with a way to signal when a write to disk fails +write: # f: fd or (addr stream byte), s: (addr array byte) + # . prologue + 55/push-ebp + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # if (s == 0) return + 81 7/subop/compare 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 0/imm32 # compare *(ebp+12) + 74/jump-if-= $write:end/disp8 + # if (f < 0x08000000) _write(f, s) and 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) + 73/jump-if-addr>= $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->size + 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->size], s) + # . . push s + ff 6/subop/push 1/mod/*+disp8 5/rm32/ebp . . . . 0xc/disp8 . # push *(ebp+12) + # . . push &f->data[f->size] + 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: + # . epilogue + 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: # (stream byte) + # current write index + 0/imm32 + # current read index + 0/imm32 + # size + 0x10/imm32 + # data (2 lines x 8 bytes/line) + 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 + +# . . vim:nowrap:textwidth=0 |