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diff --git a/blog/asm/1.html b/blog/asm/1.html index c4b0bf6..d46759f 100644 --- a/blog/asm/1.html +++ b/blog/asm/1.html @@ -3,7 +3,7 @@ "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"> <html xmlns="http://www.w3.org/1999/xhtml" lang="en" xml:lang="en"> <head> -<!-- 2024-03-07 Thu 20:54 --> +<!-- 2024-03-07 Thu 20:55 --> <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> @@ -23,9 +23,9 @@ <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-org826f92f" class="outline-2"> -<h2 id="org826f92f">Memory :</h2> -<div class="outline-text-2" id="text-org826f92f"> +<div id="outline-container-org924bef5" class="outline-2"> +<h2 id="org924bef5">Memory :</h2> +<div class="outline-text-2" id="text-org924bef5"> <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> @@ -40,9 +40,9 @@ Memory is a sequence of octets (Aka 8bits) that each have a unique integer assig The offset and segment are encoded in 16bits, so they take a value between 0 and 65535 </p> </div> -<div id="outline-container-orgdfce54b" class="outline-4"> -<h4 id="orgdfce54b">Important :</h4> -<div class="outline-text-4" id="text-orgdfce54b"> +<div id="outline-container-orgdfa99d1" class="outline-4"> +<h4 id="orgdfa99d1">Important :</h4> +<div class="outline-text-4" id="text-orgdfa99d1"> <p> The relation between the Effective Address and the Segment & Offset is as follow : </p> @@ -52,8 +52,8 @@ The relation between the Effective Address and the Segment & Offset is as fo </p> </div> <ul class="org-ul"> -<li><a id="org3da6d39"></a>Example :<br /> -<div class="outline-text-5" id="text-org3da6d39"> +<li><a id="org8845f88"></a>Example :<br /> +<div class="outline-text-5" id="text-org8845f88"> <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> @@ -66,16 +66,16 @@ Now if you are a clever one ( I know you are, since you are reading this <3 ) </li> </ul> </div> -<div id="outline-container-org53e7169" class="outline-3"> -<h3 id="org53e7169">Registers</h3> -<div class="outline-text-3" id="text-org53e7169"> +<div id="outline-container-org16ce372" class="outline-3"> +<h3 id="org16ce372">Registers</h3> +<div class="outline-text-3" id="text-org16ce372"> <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-org052f8dc" class="outline-4"> -<h4 id="org052f8dc">General Registers</h4> -<div class="outline-text-4" id="text-org052f8dc"> +<div id="outline-container-org8d1541d" class="outline-4"> +<h4 id="org8d1541d">General Registers</h4> +<div class="outline-text-4" id="text-org8d1541d"> <p> General registers contribute to arithmetic’s and logic and addressing too. </p> @@ -126,28 +126,28 @@ Now here are the Registers we can find in this section: </div> </div> </div> -<div id="outline-container-org2327321" class="outline-3"> -<h3 id="org2327321">Addressing and registers…again</h3> -<div class="outline-text-3" id="text-org2327321"> +<div id="outline-container-orgd61521c" class="outline-3"> +<h3 id="orgd61521c">Addressing and registers…again</h3> +<div class="outline-text-3" id="text-orgd61521c"> </div> -<div id="outline-container-orgcab6464" class="outline-4"> -<h4 id="orgcab6464">I realized what I wrote here before was almost gibberish, sooo here we go again I guess ?</h4> -<div class="outline-text-4" id="text-orgcab6464"> +<div id="outline-container-orgc573bac" class="outline-4"> +<h4 id="orgc573bac">I realized what I wrote here before was almost gibberish, sooo here we go again I guess ?</h4> +<div class="outline-text-4" id="text-orgc573bac"> <p> Well lets take a step back to the notion of effective addresses VS relative ones. </p> </div> </div> -<div id="outline-container-orgb2c4683" class="outline-4"> -<h4 id="orgb2c4683">Effective = 10h x Segment + Offset . Part1</h4> -<div class="outline-text-4" id="text-orgb2c4683"> +<div id="outline-container-org83b616a" class="outline-4"> +<h4 id="org83b616a">Effective = 10h x Segment + Offset . Part1</h4> +<div class="outline-text-4" id="text-org83b616a"> <p> When trying to access a specific memory space, we use this annotation <b>[Segment:Offset]</b>, so for example, and assuming <b>DS = 0100h</b>. We want to write the value <b>0x0005</b> to the memory space defined by the physical address <b>1234h</b>, what do we do ? </p> </div> <ul class="org-ul"> -<li><a id="orge32ff8e"></a>Answer :<br /> -<div class="outline-text-5" id="text-orge32ff8e"> +<li><a id="orga0fd499"></a>Answer :<br /> +<div class="outline-text-5" id="text-orga0fd499"> <div class="org-src-container"> <pre class="src src-asm"><span style="color: #89b4fa;">MOV</span> [DS:0234h], 0x0005 </pre> @@ -155,11 +155,16 @@ When trying to access a specific memory space, we use this annotation <b>[Segmen <p> Why ? Let’s break it down : -<img src="../../src/gifs/lain-dance.gif" alt="lain-dance.gif" /> </p> +<div id="orge5d4a33" class="figure"> +<p><img src="../../src/gifs/lain-dance.gif" alt="lain-dance.gif" /> +</p> +</div> + + <p> We Already know that <b>Effective = 10h x Segment + Offset</b>, So here we have : <b>1234h = 10h x DS + Offset</b>, we already know that <b>DS = 0100h</b>, we end up with this simple equation <b>1234h = 1000h + Offset</b>, therefor the Offset is <b>0234h</b> </p> @@ -172,9 +177,9 @@ Simple, right ?, now for another example </li> </ul> </div> -<div id="outline-container-orga49169d" class="outline-4"> -<h4 id="orga49169d">Another example :</h4> -<div class="outline-text-4" id="text-orga49169d"> +<div id="outline-container-org93b46d0" class="outline-4"> +<h4 id="org93b46d0">Another example :</h4> +<div class="outline-text-4" id="text-org93b46d0"> <p> What if we now have this instruction ? </p> @@ -187,9 +192,9 @@ What does it do ? You might or might not be surprised that it does the exact sam </p> </div> </div> -<div id="outline-container-org901ecc2" class="outline-4"> -<h4 id="org901ecc2">Segment + Register <3</h4> -<div class="outline-text-4" id="text-org901ecc2"> +<div id="outline-container-orgcba10b0" class="outline-4"> +<h4 id="orgcba10b0">Segment + Register <3</h4> +<div class="outline-text-4" id="text-orgcba10b0"> <p> Consider <b>DS = 0100h</b> and <b>BX = BP = 0234h</b> and this code snippet: </p> @@ -225,8 +230,8 @@ The General rule of thumb is as follows : </ul> </div> <ul class="org-ul"> -<li><a id="org6cd6bc8"></a>Note<br /> -<div class="outline-text-5" id="text-org6cd6bc8"> +<li><a id="orgf6c5f3b"></a>Note<br /> +<div class="outline-text-5" id="text-orgf6c5f3b"> <p> The values of the registers CS DS and SS are automatically initialized by the OS when launching the program. So these segments are implicit. AKA : If we want to access a specific data in memory, we just need to specify its offset. Also you can’t write directly into the DS or CS segment registers, so something like </p> @@ -244,7 +249,7 @@ The values of the registers CS DS and SS are automatically initialized by the OS </div> <div id="postamble" class="status"> <p class="author">Author: Crystal</p> -<p class="date">Created: 2024-03-07 Thu 20:54</p> +<p class="date">Created: 2024-03-07 Thu 20:55</p> </div> </body> </html> |