diff options
Diffstat (limited to 'linux/112read-byte.subx')
| -rw-r--r-- | linux/112read-byte.subx | 418 |
1 files changed, 418 insertions, 0 deletions
diff --git a/linux/112read-byte.subx b/linux/112read-byte.subx new file mode 100644 index 00000000..7510a9e8 --- /dev/null +++ b/linux/112read-byte.subx @@ -0,0 +1,418 @@ +# read-byte-buffered: one higher-level abstraction atop 'read'. +# +# There are many situations where 'read' is a lot to manage, and we need +# to abstract some details away. One of them is when we want to read a file +# character by character. In this situation we follow C's FILE data structure, +# which manages the underlying file descriptor together with the buffer it +# reads into. We call our version 'buffered-file'. Should be useful with other +# primitives as well, in later layers. + +== data + +# The buffered file for standard input. Also illustrates the layout for +# buffered-file: a pointer to the backing store, followed by a 'buffer' stream +Stdin: # buffered-file + # file descriptor or (addr stream byte) + 0/imm32 # standard input +$Stdin->buffer: + # inlined fields for a stream + # current write index + 0/imm32 + # current read index + 0/imm32 + # size + 8/imm32 + # 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 + +# Return next byte value in eax, with top 3 bytes cleared. +# On reaching end of file, return 0xffffffff (Eof). +read-byte-buffered: # f: (addr buffered-file) -> byte-or-Eof/eax: byte + # . prologue + 55/push-ebp + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # . save registers + 51/push-ecx + 56/push-esi + # esi = f + 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 8/disp8 . # copy *(ebp+8) to esi + # ecx = f->read + 8b/copy 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 8/disp8 . # copy *(esi+8) to ecx + # if (f->read >= f->write) populate stream from file + 3b/compare 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 4/disp8 . # compare ecx with *(esi+4) + 7c/jump-if-< $read-byte-buffered:from-stream/disp8 + # . clear-stream(stream = f+4) + # . . push args + 8d/copy-address 1/mod/*+disp8 6/rm32/esi . . . 0/r32/eax 4/disp8 . # copy esi+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 + # . f->read must now be 0; update its cache at ecx + 31/xor 3/mod/direct 1/rm32/ecx . . . 1/r32/ecx . . # clear ecx + # . eax = read(f->fd, stream = f+4) + # . . push args + 50/push-eax + ff 6/subop/push 0/mod/indirect 6/rm32/esi . . . . . . # push *esi + # . . call + e8/call read/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp + # if (eax == 0) return 0xffffffff + 3d/compare-eax-and 0/imm32 + 75/jump-if-!= $read-byte-buffered:from-stream/disp8 + b8/copy-to-eax 0xffffffff/imm32/Eof + eb/jump $read-byte-buffered:end/disp8 +$read-byte-buffered:from-stream: + # byte-or-Eof = f->data[f->read] + 31/xor 3/mod/direct 0/rm32/eax . . . 0/r32/eax . . # clear eax + 8a/copy-byte 1/mod/*+disp8 4/rm32/sib 6/base/esi 1/index/ecx . 0/r32/AL 0x10/disp8 . # copy byte at *(esi+ecx+16) to AL + # ++f->read + ff 0/subop/increment 1/mod/*+disp8 6/rm32/esi . . . . 8/disp8 . # increment *(esi+8) +$read-byte-buffered:end: + # . restore registers + 5e/pop-to-esi + 59/pop-to-ecx + # . epilogue + 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp + 5d/pop-to-ebp + c3/return + +# - tests + +test-read-byte-buffered-single: + # - check that read-byte-buffered 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->buffer) + # . . push args + 68/push $_test-buffered-file->buffer/imm32 + # . . call + e8/call clear-stream/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # . write(_test-stream, "Ab") + # . . push args + 68/push "Ab"/imm32 + 68/push _test-stream/imm32 + # . . call + e8/call write/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp + # read-byte-buffered(_test-buffered-file) + # . . push args + 68/push _test-buffered-file/imm32 + # . . call + e8/call read-byte-buffered/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # check-ints-equal(eax, 'A', msg) + # . . push args + 68/push "F - test-read-byte-buffered-single"/imm32 + 68/push 0x41/imm32 + 50/push-eax + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp + # . end + c3/return + +test-read-byte-buffered-multiple: + # - call read-byte-buffered twice, check that second call returns second byte + # setup + # . clear-stream(_test-stream) + # . . push args + 68/push _test-stream/imm32 + # . . call + e8/call clear-stream/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # . clear-stream($_test-buffered-file->buffer) + # . . push args + 68/push $_test-buffered-file->buffer/imm32 + # . . call + e8/call clear-stream/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # . write(_test-stream, "Ab") + # . . push args + 68/push "Ab"/imm32 + 68/push _test-stream/imm32 + # . . call + e8/call write/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp + # read-byte-buffered(_test-buffered-file) + # . . push args + 68/push _test-buffered-file/imm32 + # . . call + e8/call read-byte-buffered/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # read-byte-buffered(_test-buffered-file) + # . . push args + 68/push _test-buffered-file/imm32 + # . . call + e8/call read-byte-buffered/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # check-ints-equal(eax, 'b', msg) + # . . push args + 68/push "F - test-read-byte-buffered-multiple"/imm32 + 68/push 0x62/imm32 + 50/push-eax + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp + # . end + c3/return + +test-read-byte-buffered-end-of-file: + # - call read-byte-buffered on an empty 'file', check that it returns Eof + # setup + # . clear-stream(_test-stream) + # . . push args + 68/push _test-stream/imm32 + # . . call + e8/call clear-stream/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # . clear-stream($_test-buffered-file->buffer) + # . . push args + 68/push $_test-buffered-file->buffer/imm32 + # . . call + e8/call clear-stream/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # read-byte-buffered(_test-buffered-file) + # . . push args + 68/push _test-buffered-file/imm32 + # . . call + e8/call read-byte-buffered/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # check-ints-equal(eax, 0xffffffff, msg) + # . . push args + 68/push "F - test-read-byte-buffered-end-of-file"/imm32 + 68/push 0xffffffff/imm32/Eof + 50/push-eax + # . . call + e8/call check-ints-equal/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 0xc/imm32 # add to esp + # . end + c3/return + +test-read-byte-buffered-refills-buffer: + # - consume buffered-file's buffer, check that next read-byte-buffered still works + # setup + # . clear-stream(_test-stream) + # . . push args + 68/push _test-stream/imm32 + # . . call + e8/call clear-stream/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # . clear-stream($_test-buffered-file->buffer) + # . . push args + 68/push $_test-buffered-file->buffer/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, "Abcdefgh") + # . . push args + 68/push "Abcdefgh"/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 + # pretend buffer is full + # . _test-buffered-file->read = 6 # >= _test-buffered-file->size + b8/copy-to-eax _test-buffered-file/imm32 + c7 0/subop/copy 1/mod/*+disp8 0/rm32/eax . . . . 8/disp8 6/imm32 # copy to *(eax+8) + # read-byte-buffered(_test-buffered-file) + # . . push args + 68/push _test-buffered-file/imm32 + # . . call + e8/call read-byte-buffered/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 4/imm32 # add to esp + # check-ints-equal(eax, 'A', msg) + # . . push args + 68/push "F - test-read-byte-buffered-refills-buffer"/imm32 + 68/push 0x41/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 + # . end + c3/return + +# Return next byte value in eax, with top 3 bytes cleared. +# Abort on reaching end of stream. +read-byte: # s: (addr stream byte) -> result/eax: byte + # . prologue + 55/push-ebp + 89/copy 3/mod/direct 5/rm32/ebp . . . 4/r32/esp . . # copy esp to ebp + # . save registers + 51/push-ecx + 56/push-esi + # esi = s + 8b/copy 1/mod/*+disp8 5/rm32/ebp . . . 6/r32/esi 8/disp8 . # copy *(ebp+8) to esi + # ecx = s->read + 8b/copy 1/mod/*+disp8 6/rm32/esi . . . 1/r32/ecx 4/disp8 . # copy *(esi+4) to ecx + # if (f->read >= f->write) abort + 3b/compare 0/mod/indirect 6/rm32/esi . . . 1/r32/ecx . . # compare ecx with *esi + 0f 8d/jump-if->= $read-byte:abort/disp32 + # result = f->data[f->read] + 31/xor 3/mod/direct 0/rm32/eax . . . 0/r32/eax . . # clear eax + 8a/copy-byte 1/mod/*+disp8 4/rm32/sib 6/base/esi 1/index/ecx . 0/r32/AL 0xc/disp8 . # copy byte at *(esi+ecx+12) to AL + # ++f->read + ff 0/subop/increment 1/mod/*+disp8 6/rm32/esi . . . . 4/disp8 . # increment *(esi+4) +$read-byte:end: + # . restore registers + 5e/pop-to-esi + 59/pop-to-ecx + # . epilogue + 89/copy 3/mod/direct 4/rm32/esp . . . 5/r32/ebp . . # copy ebp to esp + 5d/pop-to-ebp + c3/return + +$read-byte:abort: + # . _write(2/stderr, error) + # . . push args + 68/push "read-byte: empty stream\n"/imm32 + 68/push 2/imm32/stderr + # . . call + e8/call _write/disp32 + # . . discard args + 81 0/subop/add 3/mod/direct 4/rm32/esp . . . . . 8/imm32 # add to esp + # . syscall(exit, 1) + bb/copy-to-ebx 1/imm32 + e8/call syscall_exit/disp32 + # never gets here + +== data + +# a test buffered file for _test-stream +_test-buffered-file: # buffered-file + # file descriptor or (addr stream byte) + _test-stream/imm32 +$_test-buffered-file->buffer: + # current write index + 0/imm32 + # current read index + 0/imm32 + # size + 6/imm32 + # data + 00 00 00 00 00 00 # 6 bytes + +_test-input-stream: # (stream byte) + # current write index + 0/imm32 + # current read index + 0/imm32 + # size + 0x400/imm32 # 1024 bytes + # data (64 lines x 16 bytes/line) + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 + +# a test buffered file for _test-input-stream +_test-input-buffered-file: # buffered-file + # file descriptor or (addr stream byte) + _test-input-stream/imm32 +$_test-input-buffered-file->buffer: + # current write index + 0/imm32 + # current read index + 0/imm32 + # size + 6/imm32 + # data + 00 00 00 00 00 00 # 6 bytes + +# . . vim:nowrap:textwidth=0 |