Mu - linux/108write.subx

From 3350c34a74844e21ea69077e01efff3bae64bdcd Mon Sep 17 00:00:00 2001 From: Kartik Agaram Date: Tue, 23 Mar 2021 17:31:08 -0700 Subject: . --- html/linux/108write.subx.html | 226 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 226 insertions(+) create mode 100644 html/linux/108write.subx.html (limited to 'html/linux/108write.subx.html') diff --git a/html/linux/108write.subx.html b/html/linux/108write.subx.html new file mode 100644 index 00000000..2dcb11f1 --- /dev/null +++ b/html/linux/108write.subx.html @@ -0,0 +1,226 @@ + + + + +Mu - linux/108write.subx + + + + + + + + + + +https://github.com/akkartik/mu/blob/main/linux/108write.subx +
+  1 # write: like _write, but also support in-memory streams in addition to file
+  2 # descriptors.
+  3 #
+  4 # Our first dependency-injected and testable primitive. We can pass it either
+  5 # a file descriptor or an address to a stream. If a file descriptor is passed
+  6 # in, we _write to it using the right syscall. If a 'fake file descriptor' or
+  7 # stream is passed in, we append to the stream. This lets us redirect output
+  8 # in tests and check it later.
+  9 #
+ 10 # We assume our data segment will never begin at an address shorter than
+ 11 # 0x08000000, so any smaller arguments are assumed to be real file descriptors.
+ 12 #
+ 13 # A stream looks like this:
+ 14 #   read: int  # index at which to read next
+ 15 #   write: int  # index at which writes go
+ 16 #   data: (array byte)  # prefixed by size as usual
+ 17 
+ 18 == code
+ 19 #   instruction                     effective address                                                   register    displacement    immediate
+ 20 # . op          subop               mod             rm32          base        index         scale       r32
+ 21 # . 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
+ 22 
+ 23 # TODO: come up with a way to signal when a write to disk fails
+ 24 write:  # f: fd or (addr stream byte), s: (addr array byte)
+ 25     # . prologue
+ 26     55/push-ebp
+ 27     89/copy                         3/mod/direct    5/rm32/ebp    .           .             .           4/r32/esp   .               .                 # copy esp to ebp
+ 28     # if (s == 0) return
+ 29     81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       0/imm32           # compare *(ebp+12)
+ 30     74/jump-if-=  $write:end/disp8
+ 31     # if (f < 0x08000000) _write(f, s) and return  # f can't be a user-mode address, so treat it as a kernel file descriptor
+ 32     81          7/subop/compare     1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         0x08000000/imm32  # compare *(ebp+8)
+ 33     73/jump-if-addr>=  $write:fake/disp8
+ 34     # . . push args
+ 35     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
+ 36     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           8/disp8         .                 # push *(ebp+8)
+ 37     # . . call
+ 38     e8/call  _write/disp32
+ 39     # . . discard args
+ 40     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+ 41     eb/jump  $write:end/disp8
+ 42 $write:fake:
+ 43     # otherwise, treat 'f' as a stream to append to
+ 44     # . save registers
+ 45     50/push-eax
+ 46     51/push-ecx
+ 47     52/push-edx
+ 48     53/push-ebx
+ 49     # ecx = f
+ 50     8b/copy                         1/mod/*+disp8   5/rm32/ebp    .           .                         1/r32/ecx   8/disp8         .                 # copy *(ebp+8) to ecx
+ 51     # edx = f->write
+ 52     8b/copy                         0/mod/indirect  1/rm32/ecx    .           .             .           2/r32/edx   .               .                 # copy *ecx to edx
+ 53     # ebx = f->size
+ 54     8b/copy                         1/mod/*+disp8   1/rm32/ecx    .           .             .           3/r32/ebx   8/disp8         .                 # copy *(ecx+8) to ebx
+ 55     # eax = _append-3(&f->data[f->write], &f->data[f->size], s)
+ 56     # . . push s
+ 57     ff          6/subop/push        1/mod/*+disp8   5/rm32/ebp    .           .             .           .           0xc/disp8       .                 # push *(ebp+12)
+ 58     # . . push &f->data[f->size]
+ 59     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
+ 60     53/push-ebx
+ 61     # . . push &f->data[f->write]
+ 62     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
+ 63     53/push-ebx
+ 64     # . . call
+ 65     e8/call  _append-3/disp32
+ 66     # . . discard args
+ 67     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+ 68     # f->write += eax
+ 69     01/add                          0/mod/indirect  1/rm32/ecx    .           .             .           0/r32/eax   .               .                 # add eax to *ecx
+ 70     # . restore registers
+ 71     5b/pop-to-ebx
+ 72     5a/pop-to-edx
+ 73     59/pop-to-ecx
+ 74     58/pop-to-eax
+ 75 $write:end:
+ 76     # . epilogue
+ 77     89/copy                         3/mod/direct    4/rm32/esp    .           .             .           5/r32/ebp   .               .                 # copy ebp to esp
+ 78     5d/pop-to-ebp
+ 79     c3/return
+ 80 
+ 81 test-write-single:
+ 82     # clear-stream(_test-stream)
+ 83     # . . push args
+ 84     68/push  _test-stream/imm32
+ 85     # . . call
+ 86     e8/call  clear-stream/disp32
+ 87     # . . discard args
+ 88     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+ 89     # write(_test-stream, "Ab")
+ 90     # . . push args
+ 91     68/push  "Ab"/imm32
+ 92     68/push  _test-stream/imm32
+ 93     # . . call
+ 94     e8/call  write/disp32
+ 95     # . . discard args
+ 96     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+ 97     # check-ints-equal(*_test-stream->data, 41/A 62/b 00 00, msg)
+ 98     # . . push args
+ 99     68/push  "F - test-write-single"/imm32
+100     68/push  0x006241/imm32/Ab
+101     # . . push *_test-stream->data
+102     b8/copy-to-eax  _test-stream/imm32
+103     ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           0xc/disp8       .                 # push *(eax+12)
+104     # . . call
+105     e8/call  check-ints-equal/disp32
+106     # . . discard args
+107     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+108     # end
+109     c3/return
+110 
+111 test-write-appends:
+112     # clear-stream(_test-stream)
+113     # . . push args
+114     68/push  _test-stream/imm32
+115     # . . call
+116     e8/call  clear-stream/disp32
+117     # . . discard args
+118     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               4/imm32           # add to esp
+119     # write(_test-stream, "C")
+120     # . . push args
+121     68/push  "C"/imm32
+122     68/push  _test-stream/imm32
+123     # . . call
+124     e8/call  write/disp32
+125     # . . discard args
+126     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+127     # write(_test-stream, "D")
+128     # . . push args
+129     68/push  "D"/imm32
+130     68/push  _test-stream/imm32
+131     # . . call
+132     e8/call  write/disp32
+133     # . . discard args
+134     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               8/imm32           # add to esp
+135     # check-ints-equal(*_test-stream->data, 43/C 44/D 00 00, msg)
+136     # . . push args
+137     68/push  "F - test-write-appends"/imm32
+138     68/push  0x00004443/imm32/C-D
+139     # . . push *_test-stream->data
+140     b8/copy-to-eax  _test-stream/imm32
+141     ff          6/subop/push        1/mod/*+disp8   0/rm32/eax    .           .             .           .           0xc/disp8       .                 # push *(eax+12)
+142     # . . call
+143     e8/call  check-ints-equal/disp32
+144     # . . discard args
+145     81          0/subop/add         3/mod/direct    4/rm32/esp    .           .             .           .           .               0xc/imm32         # add to esp
+146     # end
+147     c3/return
+148 
+149 == data
+150 
+151 _test-stream:  # (stream byte)
+152     # current write index
+153     0/imm32
+154     # current read index
+155     0/imm32
+156     # size
+157     0x10/imm32
+158     # data (2 lines x 8 bytes/line)
+159     00 00 00 00 00 00 00 00
+160     00 00 00 00 00 00 00 00
+161 
+162 # . . vim:nowrap:textwidth=0
+
+ + + -- cgit 1.4.1-2-gfad0