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authorCrystal <crystal@wizard.tower>2024-02-24 17:36:27 +0100
committerCrystal <crystal@wizard.tower>2024-02-24 17:36:27 +0100
commit9c369129fc44ce90088476387cd54665035a9505 (patch)
tree152e595a0660ccd482884c5db14d7dce15be7dc6
parentd76770c2a56bcc5cb795661d76e24f6116f26154 (diff)
downloadwww-9c369129fc44ce90088476387cd54665035a9505.tar.gz
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+<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
+"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
+<html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en">
+<head>
+<!-- 2024-02-24 Sat 17:36 -->
+<meta http-equiv="Content-Type" content="text/html;charset=utf-8" />
+<meta name="viewport" content="width=device-width, initial-scale=1" />
+<title>x86 Assembly from my understanding</title>
+<meta name="author" content="Crystal" />
+<meta name="generator" content="Org Mode" />
+<link rel="stylesheet" type="text/css" href="../../src/css/colors.css"/>
+<link rel="stylesheet" type="text/css" href="../../src/css/style.css"/>
+<link rel="icon" type="image/x-icon" href="../../../favicon.png">
+</head>
+<body>
+<div id="org-div-home-and-up">
+ <a accesskey="h" href=""> UP </a>
+ |
+ <a accesskey="H" href="https://crystal.tilde.institute/"> HOME </a>
+</div><div id="content" class="content">
+<h1 class="title">x86 Assembly from my understanding</h1>
+<p>
+Soooo this article (or maybe even a series of articles, who knows ?) will be about x86 assembly, or rather, what I understood from it and my road from the bottom-up hopefully reaching a good level of understanding
+</p>
+<div id="outline-container-org8392211" class="outline-2">
+<h2 id="org8392211">Memory :</h2>
+<div class="outline-text-2" id="text-org8392211">
+<p>
+Memory is a sequence of octets (Aka 8bits) that each have a unique integer assigned to them called <b>The Effective Address (EA)</b>, in this particular CPU Architecture (the i8086), the octet is designated by a couple (A segment number, and the offset in the segment)
+</p>
+
+
+<ul class="org-ul">
+<li>The Segment is a set of 64 consecutive Koctets (1 Koctet = 1024 octets).</li>
+<li>And the offset is to specify the particular octet in that segment.</li>
+</ul>
+
+<p>
+The offset and segment are encoded in 16bits, so they take a value between 0 and 65535
+</p>
+</div>
+<div id="outline-container-orgb021039" class="outline-4">
+<h4 id="orgb021039">Important :</h4>
+<div class="outline-text-4" id="text-orgb021039">
+<p>
+The relation between the Effective Address and the Segment &amp; Offset is as follow :
+</p>
+
+<p>
+<b><b>Effective address = 16 x segment + offset</b></b> keep in mind that this equation is encoded in decimal, which will change soon as we use Hexadecimal for convention reasons.
+</p>
+</div>
+<ul class="org-ul">
+<li><a id="orgda02cd3"></a>Example :<br />
+<div class="outline-text-5" id="text-orgda02cd3">
+<p>
+Let the Physical address (Or Effective Address, these two terms are enterchangeable) <b>12345h</b> (the h refers to Hexadecimal, which can also be written like this <b>0x12345</b>), the register <b>DS = 1230h</b> and the register <b>SI = 0045h</b>, the CPU calculates the physical address by multiplying the content of the segment register <b>DS</b> by 10h (or 16) and adding the content of the register <b>SI</b>. so we get : <b>1230h x 10h + 45h = 12345h</b>
+</p>
+
+
+<p>
+Now if you are a clever one ( I know you are, since you are reading this &lt;3 ) you may say that the physical address <b>12345h</b> can be written in more than one way&#x2026;.and you are right, more precisely : <b>2<sup>12</sup> = 4096</b> different ways !!!
+</p>
+</div>
+</li>
+</ul>
+</div>
+<div id="outline-container-orgd56c9fa" class="outline-3">
+<h3 id="orgd56c9fa">Registers</h3>
+<div class="outline-text-3" id="text-orgd56c9fa">
+<p>
+The 8086 CPU has 14 registers of 16bits of size. From the POV of the user, the 8086 has 3 groups of 4 registers of 16bits. One state register of 9bits and a counting program of 16bits inaccessible to the user (whatever this means).
+</p>
+</div>
+<div id="outline-container-orgd10cc4b" class="outline-4">
+<h4 id="orgd10cc4b">General Registers</h4>
+<div class="outline-text-4" id="text-orgd10cc4b">
+<p>
+General registers contribute to arithmetic&rsquo;s and logic and addressing too.
+</p>
+
+
+<p>
+Each half-register is accessible as a register of 8bits, therefor making the 8086 backwards compatible with the 8080 (which had 8bit registers)
+</p>
+
+
+<p>
+Now here are the Registers we can find in this section:
+</p>
+
+
+<p>
+<b>AX</b>: This is the accumulator. It is of 16 bits and is divided into two 8-bit registers AH and AL to also perform 8-bit instructions. It is generally used for arithmetical and logical instructions but in 8086 microprocessor it is not mandatory to have an accumulator as the destination operand. Example:
+</p>
+<div class="org-src-container">
+<pre class="src src-asm"><span style="color: #89b4fa;">ADD</span> <span style="color: #cba6f7;">AX</span>, AX <span style="color: #6c7086;">;</span><span style="color: #6c7086;">(AX = AX + AX)</span>
+</pre>
+</div>
+
+<p>
+<b>BX</b>: This is the base register. It is of 16 bits and is divided into two 8-bit registers BH and BL to also perform 8-bit instructions. It is used to store the value of the offset. Example:
+</p>
+<div class="org-src-container">
+<pre class="src src-asm"><span style="color: #89b4fa;">MOV</span> <span style="color: #cba6f7;">BL</span>, [<span style="color: #fab387;">500</span>] <span style="color: #6c7086;">;</span><span style="color: #6c7086;">(BL = 500H)</span>
+</pre>
+</div>
+</div>
+</div>
+</div>
+</div>
+</div>
+<div id="postamble" class="status">
+<p class="author">Author: Crystal</p>
+<p class="date">Created: 2024-02-24 Sat 17:36</p>
+</div>
+</body>
+</html>
diff --git a/src/org/blog/assembly/1.org b/src/org/blog/assembly/1.org
new file mode 100644
index 0000000..f5a1a59
--- /dev/null
+++ b/src/org/blog/assembly/1.org
@@ -0,0 +1,59 @@
+#+title: x86 Assembly from my understanding
+#+OPTIONS: ^:{}
+#+AUTHOR: Crystal
+#+OPTIONS: num:nil
+#+EXPORT_FILE_NAME: ../../../../blog/asm/1.html
+#+HTML_HEAD: <link rel="stylesheet" type="text/css" href="../../src/css/colors.css"/>
+#+HTML_HEAD: <link rel="stylesheet" type="text/css" href="../../src/css/style.css"/>
+#+OPTIONS: html-style:nil
+#+OPTIONS: toc:nil
+#+HTML_HEAD: <link rel="icon" type="image/x-icon" href="../../../favicon.png">
+#+HTML_LINK_HOME: https://crystal.tilde.institute/
+
+
+Soooo this article (or maybe even a series of articles, who knows ?) will be about x86 assembly, or rather, what I understood from it and my road from the bottom-up hopefully reaching a good level of understanding
+
+
+* Memory :
+Memory is a sequence of octets (Aka 8bits) that each have a unique integer assigned to them called *The Effective Address (EA)*, in this particular CPU Architecture (the i8086), the octet is designated by a couple (A segment number, and the offset in the segment)
+
+
+- The Segment is a set of 64 consecutive Koctets (1 Koctet = 1024 octets).
+- And the offset is to specify the particular octet in that segment.
+
+The offset and segment are encoded in 16bits, so they take a value between 0 and 65535
+
+*** Important :
+The relation between the Effective Address and the Segment & Offset is as follow :
+
+**Effective address = 16 x segment + offset** keep in mind that this equation is encoded in decimal, which will change soon as we use Hexadecimal for convention reasons.
+
+**** Example :
+Let the Physical address (Or Effective Address, these two terms are enterchangeable) *12345h* (the h refers to Hexadecimal, which can also be written like this *0x12345*), the register *DS = 1230h* and the register *SI = 0045h*, the CPU calculates the physical address by multiplying the content of the segment register *DS* by 10h (or 16) and adding the content of the register *SI*. so we get : *1230h x 10h + 45h = 12345h*
+
+
+Now if you are a clever one ( I know you are, since you are reading this <3 ) you may say that the physical address *12345h* can be written in more than one way....and you are right, more precisely : *2^{12} = 4096* different ways !!!
+
+** Registers
+
+The 8086 CPU has 14 registers of 16bits of size. From the POV of the user, the 8086 has 3 groups of 4 registers of 16bits. One state register of 9bits and a counting program of 16bits inaccessible to the user (whatever this means).
+
+*** General Registers
+General registers contribute to arithmetic's and logic and addressing too.
+
+
+Each half-register is accessible as a register of 8bits, therefor making the 8086 backwards compatible with the 8080 (which had 8bit registers)
+
+
+Now here are the Registers we can find in this section:
+
+
+*AX*: This is the accumulator. It is of 16 bits and is divided into two 8-bit registers AH and AL to also perform 8-bit instructions. It is generally used for arithmetical and logical instructions but in 8086 microprocessor it is not mandatory to have an accumulator as the destination operand. Example:
+#+BEGIN_SRC asm
+ADD AX, AX ;(AX = AX + AX)
+#+END_SRC
+
+*BX*: This is the base register. It is of 16 bits and is divided into two 8-bit registers BH and BL to also perform 8-bit instructions. It is used to store the value of the offset. Example:
+#+BEGIN_SRC asm
+MOV BL, [500] ;(BL = 500H)
+#+END_SRC