📄 bootsect.s
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<!doctype html public "-//W3C//DTD HTML 3.2//EN"><html><head><title>Linux/boot/bootsect.s</title><meta http-equiv=Content-Type content="text/html; charset=gb2312"><base href="http://oldlinux.org/lxr/http/"></head><body bgcolor=white><div align=center> [<b><i>源代码浏览</i></b>] [<a href="diff/boot/bootsect.s">区别标定</a>] [<a href="ident">标识符搜索</a>] [<a href="search">文本搜索</a>] [<a href="find">文件搜索</a>]</div><h1 align=center> <a href="http:/"> OldLinux</a> <a href="http:blurb.html"> 交叉引用</a><br> <a href="source/">Linux</a>/<a href="source/boot/">boot</a>/<a href="source/boot/bootsect.s">bootsect.s</a></h1><div align=center> <b>版本:</b> [<a href="source/boot/bootsect.s?v=1.0">1.0</a>] [<a href="source/boot/bootsect.s?v=0.99.11">0.99.11</a>] [<a href="source/boot/bootsect.s?v=0.99">0.99</a>] [<a href="source/boot/bootsect.s?v=0.97">0.97</a>] [<a href="source/boot/bootsect.s?v=0.96a">0.96a</a>] [<a href="source/boot/bootsect.s?v=0.95">0.95</a>] [<a href="source/boot/bootsect.s?v=0.12">0.12</a>] [<b><i>0.11</i></b>] [<a href="source/boot/bootsect.s?v=0.01">0.01</a>] <br> <b>体系结构:</b> [<b><i>i386</i></b>] <br></div><hr><pre> <a name=L1 href="source/boot/bootsect.s#L1">1</a> ! <a name=L2 href="source/boot/bootsect.s#L2">2</a> ! SYS_SIZE is the number of clicks (16 bytes) to be loaded. <a name=L3 href="source/boot/bootsect.s#L3">3</a> ! 0x3000 is 0x30000 bytes = 196kB, more than enough for current <a name=L4 href="source/boot/bootsect.s#L4">4</a> ! versions of linux <a name=L5 href="source/boot/bootsect.s#L5">5</a> ! <a name=L6 href="source/boot/bootsect.s#L6">6</a> SYSSIZE = 0x3000 <a name=L7 href="source/boot/bootsect.s#L7">7</a> ! <a name=L8 href="source/boot/bootsect.s#L8">8</a> ! bootsect.s (C) 1991 Linus Torvalds <a name=L9 href="source/boot/bootsect.s#L9">9</a> ! <a name=L10 href="source/boot/bootsect.s#L10">10</a> ! bootsect.s is loaded at 0x7c00 by the bios-startup routines, and moves <a name=L11 href="source/boot/bootsect.s#L11">11</a> ! iself out of the way to address 0x90000, and jumps there. <a name=L12 href="source/boot/bootsect.s#L12">12</a> ! <a name=L13 href="source/boot/bootsect.s#L13">13</a> ! It then loads 'setup' directly after itself (0x90200), and the system <a name=L14 href="source/boot/bootsect.s#L14">14</a> ! at 0x10000, using BIOS interrupts. <a name=L15 href="source/boot/bootsect.s#L15">15</a> ! <a name=L16 href="source/boot/bootsect.s#L16">16</a> ! NOTE! currently system is at most 8*65536 bytes long. This should be no <a name=L17 href="source/boot/bootsect.s#L17">17</a> ! problem, even in the future. I want to keep it simple. This 512 kB <a name=L18 href="source/boot/bootsect.s#L18">18</a> ! kernel size should be enough, especially as this doesn't contain the <a name=L19 href="source/boot/bootsect.s#L19">19</a> ! buffer cache as in minix <a name=L20 href="source/boot/bootsect.s#L20">20</a> ! <a name=L21 href="source/boot/bootsect.s#L21">21</a> ! The loader has been made as simple as possible, and continuos <a name=L22 href="source/boot/bootsect.s#L22">22</a> ! read errors will result in a unbreakable loop. Reboot by hand. It <a name=L23 href="source/boot/bootsect.s#L23">23</a> ! loads pretty fast by getting whole sectors at a time whenever possible. <a name=L24 href="source/boot/bootsect.s#L24">24</a> <a name=L25 href="source/boot/bootsect.s#L25">25</a> .globl begtext, begdata, begbss, endtext, enddata, endbss <a name=L26 href="source/boot/bootsect.s#L26">26</a> .text <a name=L27 href="source/boot/bootsect.s#L27">27</a> begtext: <a name=L28 href="source/boot/bootsect.s#L28">28</a> .data <a name=L29 href="source/boot/bootsect.s#L29">29</a> begdata: <a name=L30 href="source/boot/bootsect.s#L30">30</a> .bss <a name=L31 href="source/boot/bootsect.s#L31">31</a> begbss: <a name=L32 href="source/boot/bootsect.s#L32">32</a> .text <a name=L33 href="source/boot/bootsect.s#L33">33</a> <a name=L34 href="source/boot/bootsect.s#L34">34</a> SETUPLEN = 4 ! nr of setup-sectors <a name=L35 href="source/boot/bootsect.s#L35">35</a> BOOTSEG = 0x07c0 ! original address of boot-sector <a name=L36 href="source/boot/bootsect.s#L36">36</a> INITSEG = 0x9000 ! we move boot here - out of the way <a name=L37 href="source/boot/bootsect.s#L37">37</a> SETUPSEG = 0x9020 ! setup starts here <a name=L38 href="source/boot/bootsect.s#L38">38</a> SYSSEG = 0x1000 ! system loaded at 0x10000 (65536). <a name=L39 href="source/boot/bootsect.s#L39">39</a> ENDSEG = SYSSEG + SYSSIZE ! where to stop loading <a name=L40 href="source/boot/bootsect.s#L40">40</a> <a name=L41 href="source/boot/bootsect.s#L41">41</a> ! ROOT_DEV: 0x000 - same type of floppy as boot. <a name=L42 href="source/boot/bootsect.s#L42">42</a> ! 0x301 - first partition on first drive etc <a name=L43 href="source/boot/bootsect.s#L43">43</a> ROOT_DEV = 0x306 <a name=L44 href="source/boot/bootsect.s#L44">44</a> <a name=L45 href="source/boot/bootsect.s#L45">45</a> entry start <a name=L46 href="source/boot/bootsect.s#L46">46</a> start: <a name=L47 href="source/boot/bootsect.s#L47">47</a> mov ax,#BOOTSEG <a name=L48 href="source/boot/bootsect.s#L48">48</a> mov ds,ax <a name=L49 href="source/boot/bootsect.s#L49">49</a> mov ax,#INITSEG <a name=L50 href="source/boot/bootsect.s#L50">50</a> mov es,ax <a name=L51 href="source/boot/bootsect.s#L51">51</a> mov cx,#256 <a name=L52 href="source/boot/bootsect.s#L52">52</a> sub si,si <a name=L53 href="source/boot/bootsect.s#L53">53</a> sub di,di <a name=L54 href="source/boot/bootsect.s#L54">54</a> rep <a name=L55 href="source/boot/bootsect.s#L55">55</a> movw <a name=L56 href="source/boot/bootsect.s#L56">56</a> jmpi go,INITSEG <a name=L57 href="source/boot/bootsect.s#L57">57</a> go: mov ax,cs <a name=L58 href="source/boot/bootsect.s#L58">58</a> mov ds,ax <a name=L59 href="source/boot/bootsect.s#L59">59</a> mov es,ax <a name=L60 href="source/boot/bootsect.s#L60">60</a> ! put stack at 0x9ff00. <a name=L61 href="source/boot/bootsect.s#L61">61</a> mov ss,ax <a name=L62 href="source/boot/bootsect.s#L62">62</a> mov sp,#0xFF00 ! arbitrary value >>512 <a name=L63 href="source/boot/bootsect.s#L63">63</a> <a name=L64 href="source/boot/bootsect.s#L64">64</a> ! load the setup-sectors directly after the bootblock. <a name=L65 href="source/boot/bootsect.s#L65">65</a> ! Note that 'es' is already set up. <a name=L66 href="source/boot/bootsect.s#L66">66</a> <a name=L67 href="source/boot/bootsect.s#L67">67</a> load_setup: <a name=L68 href="source/boot/bootsect.s#L68">68</a> mov dx,#0x0000 ! drive 0, head 0 <a name=L69 href="source/boot/bootsect.s#L69">69</a> mov cx,#0x0002 ! sector 2, track 0 <a name=L70 href="source/boot/bootsect.s#L70">70</a> mov bx,#0x0200 ! address = 512, in INITSEG <a name=L71 href="source/boot/bootsect.s#L71">71</a> mov ax,#0x0200+SETUPLEN ! service 2, nr of sectors <a name=L72 href="source/boot/bootsect.s#L72">72</a> int 0x13 ! read it <a name=L73 href="source/boot/bootsect.s#L73">73</a> jnc ok_load_setup ! ok - continue <a name=L74 href="source/boot/bootsect.s#L74">74</a> mov dx,#0x0000 <a name=L75 href="source/boot/bootsect.s#L75">75</a> mov ax,#0x0000 ! reset the diskette <a name=L76 href="source/boot/bootsect.s#L76">76</a> int 0x13 <a name=L77 href="source/boot/bootsect.s#L77">77</a> j load_setup <a name=L78 href="source/boot/bootsect.s#L78">78</a> <a name=L79 href="source/boot/bootsect.s#L79">79</a> ok_load_setup: <a name=L80 href="source/boot/bootsect.s#L80">80</a> <a name=L81 href="source/boot/bootsect.s#L81">81</a> ! Get disk drive parameters, specifically nr of sectors/track <a name=L82 href="source/boot/bootsect.s#L82">82</a> <a name=L83 href="source/boot/bootsect.s#L83">83</a> mov dl,#0x00 <a name=L84 href="source/boot/bootsect.s#L84">84</a> mov ax,#0x0800 ! AH=8 is get drive parameters <a name=L85 href="source/boot/bootsect.s#L85">85</a> int 0x13 <a name=L86 href="source/boot/bootsect.s#L86">86</a> mov ch,#0x00 <a name=L87 href="source/boot/bootsect.s#L87">87</a> seg cs <a name=L88 href="source/boot/bootsect.s#L88">88</a> mov sectors,cx <a name=L89 href="source/boot/bootsect.s#L89">89</a> mov ax,#INITSEG <a name=L90 href="source/boot/bootsect.s#L90">90</a> mov es,ax <a name=L91 href="source/boot/bootsect.s#L91">91</a> <a name=L92 href="source/boot/bootsect.s#L92">92</a> ! Print some inane message <a name=L93 href="source/boot/bootsect.s#L93">93</a> <a name=L94 href="source/boot/bootsect.s#L94">94</a> mov ah,#0x03 ! read cursor pos <a name=L95 href="source/boot/bootsect.s#L95">95</a> xor bh,bh <a name=L96 href="source/boot/bootsect.s#L96">96</a> int 0x10 <a name=L97 href="source/boot/bootsect.s#L97">97</a> <a name=L98 href="source/boot/bootsect.s#L98">98</a> mov cx,#24 <a name=L99 href="source/boot/bootsect.s#L99">99</a> mov bx,#0x0007 ! page 0, attribute 7 (normal)<a name=L100 href="source/boot/bootsect.s#L100">100</a> mov bp,#msg1<a name=L101 href="source/boot/bootsect.s#L101">101</a> mov ax,#0x1301 ! write string, move cursor<a name=L102 href="source/boot/bootsect.s#L102">102</a> int 0x10<a name=L103 href="source/boot/bootsect.s#L103">103</a> <a name=L104 href="source/boot/bootsect.s#L104">104</a> ! ok, we've written the message, now<a name=L105 href="source/boot/bootsect.s#L105">105</a> ! we want to load the system (at 0x10000)<a name=L106 href="source/boot/bootsect.s#L106">106</a> <a name=L107 href="source/boot/bootsect.s#L107">107</a> mov ax,#SYSSEG<a name=L108 href="source/boot/bootsect.s#L108">108</a> mov es,ax ! segment of 0x010000<a name=L109 href="source/boot/bootsect.s#L109">109</a> call read_it<a name=L110 href="source/boot/bootsect.s#L110">110</a> call kill_motor<a name=L111 href="source/boot/bootsect.s#L111">111</a> <a name=L112 href="source/boot/bootsect.s#L112">112</a> ! After that we check which root-device to use. If the device is<a name=L113 href="source/boot/bootsect.s#L113">113</a> ! defined (!= 0), nothing is done and the given device is used.<a name=L114 href="source/boot/bootsect.s#L114">114</a> ! Otherwise, either /dev/PS0 (2,28) or /dev/at0 (2,8), depending<a name=L115 href="source/boot/bootsect.s#L115">115</a> ! on the number of sectors that the BIOS reports currently.<a name=L116 href="source/boot/bootsect.s#L116">116</a> <a name=L117 href="source/boot/bootsect.s#L117">117</a> seg cs<a name=L118 href="source/boot/bootsect.s#L118">118</a> mov ax,root_dev<a name=L119 href="source/boot/bootsect.s#L119">119</a> cmp ax,#0<a name=L120 href="source/boot/bootsect.s#L120">120</a> jne root_defined⌨️ 快捷键说明
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