about summary refs log tree commit diff stats
path: root/html/101_write.subx.html
blob: c992256b692ea21886b13772c3242259b2098e3d (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<title>Mu - 101_write.subx</title>
<meta name="Generator" content="Vim/8.1">
<meta name="plugin-version" content="vim8.1_v1">
<meta name="syntax" content="none">
<meta name="settings" content="number_lines,use_css,no_foldcolumn,expand_tabs,line_ids,prevent_copy=">
<meta name="colorscheme" content="minimal-light">
<style type="text/css">
<!--
pre { font-family: monospace; color: #000000; background-color: #c6c6c6; }
body { font-size:12pt; font-family: monospace; color: #000000; background-color: #c6c6c6; }
a { color:inherit; }
* { font-size:12pt; font-size: 1em; }
.subxComment { color: #005faf; }
.subxS2Comment { color: #8a8a8a; }
.LineNr { }
.subxS1Comment { color: #0000af; }
.Constant { color: #008787; }
.SpecialChar { color: #d70000; }
.subxMinorFunction { color: #875f5f; }
.Normal { color: #000000; background-color: #c6c6c6; padding-bottom: 1px; }
-->
</style>

<script type='text/javascript'>
<!--

/* function to open any folds containing a jumped-to line before jumping to it */
function JumpToLine()
{
  var lineNum;
  lineNum = window.location.hash;
  lineNum = lineNum.substr(1); /* strip off '#' */

  if (lineNum.indexOf('L') == -1) {
    lineNum = 'L'+lineNum;
  }
  var lineElem = document.getElementById(lineNum);
  /* Always jump to new location even if the line was hidden inside a fold, or
   * we corrected the raw number to a line ID.
   */
  if (lineElem) {
    lineElem.scrollIntoView(true);
  }
  return true;
}
if ('onhashchange' in window) {
  window.onhashchange = JumpToLine;
}

-->
</script>
</head>
<body onload='JumpToLine();'>
<a href='https://github.com/akkartik/mu/blob/main/101_write.subx'>https://github.com/akkartik/mu/blob/main/101_write.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment"># _write: write to a file descriptor (fd)</span>
<span id="L2" class="LineNr"> 2 </span>
<span id="L3" class="LineNr"> 3 </span>== code
<span id="L4" class="LineNr"> 4 </span><span class="subxComment">#   instruction                     effective address                                                   register    displacement    immediate</span>
<span id="L5" class="LineNr"> 5 </span><span class="subxS1Comment"># . op          subop               mod             rm32          base        index         scale       r32</span>
<span id="L6" class="LineNr"> 6 </span><span class="subxS1Comment"># . 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</span>
<span id="L7" class="LineNr"> 7 </span>
<span id="L8" class="LineNr"> 8 </span><span class="SpecialChar">Entry</span>:  <span class="subxComment"># just exit; can't test _write just yet</span>
<span id="L9" class="LineNr"> 9 </span>    bb/copy-to-ebx  0/imm32
<span id="L10" class="LineNr">10 </span>    e8/call  syscall_exit/disp32
<span id="L11" class="LineNr">11 </span>
<span id="L12" class="LineNr">12 </span><span class="subxMinorFunction">_write</span>:  <span class="subxComment"># fd: int, s: (addr array byte)</span>
<span id="L13" class="LineNr">13 </span>    <span class="subxS1Comment"># . prologue</span>
<span id="L14" class="LineNr">14 </span>    55/push-ebp
<span id="L15" class="LineNr">15 </span>    89/copy                         3/mod/direct    5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          4/r32/esp  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy esp to ebp</span>
<span id="L16" class="LineNr">16 </span>    <span class="subxS1Comment"># . save registers</span>
<span id="L17" class="LineNr">17 </span>    50/push-eax
<span id="L18" class="LineNr">18 </span>    51/push-ecx
<span id="L19" class="LineNr">19 </span>    52/push-edx
<span id="L20" class="LineNr">20 </span>    53/push-ebx
<span id="L21" class="LineNr">21 </span>    <span class="subxComment"># syscall(write, fd, (data) s+4, (size) *s)</span>
<span id="L22" class="LineNr">22 </span>    <span class="subxS1Comment"># . ebx = fd</span>
<span id="L23" class="LineNr">23 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          3/r32/ebx   8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+8) to ebx</span>
<span id="L24" class="LineNr">24 </span>    <span class="subxS1Comment"># . var data/ecx: (addr byte) = s+4</span>
<span id="L25" class="LineNr">25 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          1/r32/ecx   0xc/disp8      <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+12) to ecx</span>
<span id="L26" class="LineNr">26 </span>    81          0/subop/add         3/mod/direct    1/rm32/ecx   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>         <span class="Normal"> . </span>              4/imm32           <span class="subxComment"># add to ecx</span>
<span id="L27" class="LineNr">27 </span>    <span class="subxS1Comment"># . var size/edx: int = *s</span>
<span id="L28" class="LineNr">28 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          2/r32/edx   0xc/disp8      <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+12) to edx</span>
<span id="L29" class="LineNr">29 </span>    8b/copy                         0/mod/indirect  2/rm32/edx   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          2/r32/edx  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy *edx to edx</span>
<span id="L30" class="LineNr">30 </span>    <span class="subxS1Comment"># . syscall</span>
<span id="L31" class="LineNr">31 </span>    e8/call  syscall_write/disp32
<span id="L32" class="LineNr">32 </span>    <span class="subxComment"># if (eax &lt; 0) abort</span>
<span id="L33" class="LineNr">33 </span>    3d/compare-eax-with  0/imm32
<span id="L34" class="LineNr">34 </span>    0f 8c/jump-if-&lt;  $_write:abort/disp32
<span id="L35" class="LineNr">35 </span><span class="Constant">$_write:end</span>:
<span id="L36" class="LineNr">36 </span>    <span class="subxS1Comment"># . restore registers</span>
<span id="L37" class="LineNr">37 </span>    5b/pop-to-ebx
<span id="L38" class="LineNr">38 </span>    5a/pop-to-edx
<span id="L39" class="LineNr">39 </span>    59/pop-to-ecx
<span id="L40" class="LineNr">40 </span>    58/pop-to-eax
<span id="L41" class="LineNr">41 </span>    <span class="subxS1Comment"># . epilogue</span>
<span id="L42" class="LineNr">42 </span>    89/copy                         3/mod/direct    4/rm32/esp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          5/r32/ebp  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># copy ebp to esp</span>
<span id="L43" class="LineNr">43 </span>    5d/pop-to-ebp
<span id="L44" class="LineNr">44 </span>    c3/return
<span id="L45" class="LineNr">45 </span>
<span id="L46" class="LineNr">46 </span><span class="Constant">$_write:abort</span>:
<span id="L47" class="LineNr">47 </span>    <span class="subxComment"># can't write a message here for risk of an infinite loop, so we'll use a special exit code instead</span>
<span id="L48" class="LineNr">48 </span>    <span class="subxS1Comment"># . syscall(exit, 255)</span>
<span id="L49" class="LineNr">49 </span>    bb/copy-to-ebx  0xff/imm32
<span id="L50" class="LineNr">50 </span>    e8/call  syscall_exit/disp32
<span id="L51" class="LineNr">51 </span>    <span class="subxComment"># never gets here</span>
<span id="L52" class="LineNr">52 </span>
<span id="L53" class="LineNr">53 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
</pre>
</body>
</html>
<!-- vim: set foldmethod=manual : -->