about summary refs log tree commit diff stats
path: root/html/baremetal/112read-byte.subx.html
blob: 06271ee02968b9850bdb70cd27a227af1d9b55c6 (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
<!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 - baremetal/112read-byte.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; }
.subxS1Comment { color: #0000af; }
.subxS2Comment { color: #8a8a8a; }
.LineNr { }
.Constant { color: #008787; }
.subxFunction { color: #af5f00; text-decoration: underline; }
.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/baremetal/112read-byte.subx'>https://github.com/akkartik/mu/blob/main/baremetal/112read-byte.subx</a>
<pre id='vimCodeElement'>
<span id="L1" class="LineNr"> 1 </span><span class="subxComment">#   instruction                     effective address                                                   register    displacement    immediate</span>
<span id="L2" class="LineNr"> 2 </span><span class="subxS1Comment"># . op          subop               mod             rm32          base        index         scale       r32</span>
<span id="L3" class="LineNr"> 3 </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="L4" class="LineNr"> 4 </span>
<span id="L5" class="LineNr"> 5 </span><span class="subxComment"># TODO: read-byte-buffered</span>
<span id="L6" class="LineNr"> 6 </span>
<span id="L7" class="LineNr"> 7 </span><span class="subxComment"># Return next byte value in eax, with top 3 bytes cleared.</span>
<span id="L8" class="LineNr"> 8 </span><span class="subxComment"># Abort on reaching end of stream.</span>
<span id="L9" class="LineNr"> 9 </span><span class="subxFunction">read-byte</span>:  <span class="subxComment"># s: (addr stream byte) -&gt; result/eax: byte</span>
<span id="L10" class="LineNr">10 </span>    <span class="subxS1Comment"># . prologue</span>
<span id="L11" class="LineNr">11 </span>    55/push-ebp
<span id="L12" class="LineNr">12 </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="L13" class="LineNr">13 </span>    <span class="subxS1Comment"># . save registers</span>
<span id="L14" class="LineNr">14 </span>    51/push-ecx
<span id="L15" class="LineNr">15 </span>    56/push-esi
<span id="L16" class="LineNr">16 </span>    <span class="subxComment"># esi = s</span>
<span id="L17" class="LineNr">17 </span>    8b/copy                         1/mod/*+disp8   5/rm32/ebp   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          6/r32/esi   8/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(ebp+8) to esi</span>
<span id="L18" class="LineNr">18 </span>    <span class="subxComment"># ecx = s-&gt;read</span>
<span id="L19" class="LineNr">19 </span>    8b/copy                         1/mod/*+disp8   6/rm32/esi   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          1/r32/ecx   4/disp8        <span class="Normal"> . </span>                <span class="subxComment"># copy *(esi+4) to ecx</span>
<span id="L20" class="LineNr">20 </span>    <span class="subxComment"># if (f-&gt;read &gt;= f-&gt;write) abort</span>
<span id="L21" class="LineNr">21 </span>    3b/compare                      0/mod/indirect  6/rm32/esi   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          1/r32/ecx  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># compare ecx with *esi</span>
<span id="L22" class="LineNr">22 </span>    0f 8d/jump-if-&gt;=  $read-byte:end/disp32  <span class="subxComment"># TODO: abort</span>
<span id="L23" class="LineNr">23 </span>    <span class="subxComment"># result = f-&gt;data[f-&gt;read]</span>
<span id="L24" class="LineNr">24 </span>    31/xor                          3/mod/direct    0/rm32/eax   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>          0/r32/eax  <span class="Normal"> . </span>             <span class="Normal"> . </span>                <span class="subxComment"># clear eax</span>
<span id="L25" class="LineNr">25 </span>    8a/copy-byte                    1/mod/*+disp8   4/rm32/sib    6/base/esi  1/index/ecx  <span class="Normal"> . </span>          0/r32/AL    0xc/disp8      <span class="Normal"> . </span>                <span class="subxComment"># copy byte at *(esi+ecx+12) to AL</span>
<span id="L26" class="LineNr">26 </span>    <span class="subxComment"># ++f-&gt;read</span>
<span id="L27" class="LineNr">27 </span>    ff          0/subop/increment   1/mod/*+disp8   6/rm32/esi   <span class="Normal"> . </span>         <span class="Normal"> . </span>           <span class="Normal"> . </span>         <span class="Normal"> . </span>          4/disp8        <span class="Normal"> . </span>                <span class="subxComment"># increment *(esi+4)</span>
<span id="L28" class="LineNr">28 </span><span class="Constant">$read-byte:end</span>:
<span id="L29" class="LineNr">29 </span>    <span class="subxS1Comment"># . restore registers</span>
<span id="L30" class="LineNr">30 </span>    5e/pop-to-esi
<span id="L31" class="LineNr">31 </span>    59/pop-to-ecx
<span id="L32" class="LineNr">32 </span>    <span class="subxS1Comment"># . epilogue</span>
<span id="L33" class="LineNr">33 </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="L34" class="LineNr">34 </span>    5d/pop-to-ebp
<span id="L35" class="LineNr">35 </span>    c3/return
<span id="L36" class="LineNr">36 </span>
<span id="L37" class="LineNr">37 </span><span class="subxS2Comment"># . . vim&#0058;nowrap:textwidth=0</span>
</pre>
</body>
</html>
<!-- vim: set foldmethod=manual : -->