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| author | Crystal <crystal@wizard.tower> | 2024-03-17 21:46:44 +0100 |
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| committer | Crystal <crystal@wizard.tower> | 2024-03-17 21:46:44 +0100 |
| commit | e8c190c8b2984cd562ba65890ad86213a13b9e72 (patch) | |
| tree | ce0b881ede4f9c8b8b49989db4dc404a0acf4850 /blog/asm/1.html | |
| parent | 8347b8d1f799e38d8ce88da706460ccd8aa7f8d3 (diff) | |
| download | www-e8c190c8b2984cd562ba65890ad86213a13b9e72.tar.gz | |
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Diffstat (limited to 'blog/asm/1.html')
| -rw-r--r-- | blog/asm/1.html | 74 |
1 files changed, 37 insertions, 37 deletions
diff --git a/blog/asm/1.html b/blog/asm/1.html index d46759f..fcaae55 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 20:55 --> +<!-- 2024-03-17 Sun 21:28 --> <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-org924bef5" class="outline-2"> -<h2 id="org924bef5">Memory :</h2> -<div class="outline-text-2" id="text-org924bef5"> +<div id="outline-container-orgd547ad6" class="outline-2"> +<h2 id="orgd547ad6">Memory :</h2> +<div class="outline-text-2" id="text-orgd547ad6"> <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-orgdfa99d1" class="outline-4"> -<h4 id="orgdfa99d1">Important :</h4> -<div class="outline-text-4" id="text-orgdfa99d1"> +<div id="outline-container-org024e482" class="outline-4"> +<h4 id="org024e482">Important :</h4> +<div class="outline-text-4" id="text-org024e482"> <p> The relation between the Effective Address and the Segment & Offset is as follow : </p> @@ -52,10 +52,10 @@ The relation between the Effective Address and the Segment & Offset is as fo </p> </div> <ul class="org-ul"> -<li><a id="org8845f88"></a>Example :<br /> -<div class="outline-text-5" id="text-org8845f88"> +<li><a id="org6cfa3c7"></a>Example :<br /> +<div class="outline-text-5" id="text-org6cfa3c7"> <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> +Let the Physical address (Or Effective Address, these two terms are interchangeable) <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-org16ce372" class="outline-3"> -<h3 id="org16ce372">Registers</h3> -<div class="outline-text-3" id="text-org16ce372"> +<div id="outline-container-org6b34cdf" class="outline-3"> +<h3 id="org6b34cdf">Registers</h3> +<div class="outline-text-3" id="text-org6b34cdf"> <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-org8d1541d" class="outline-4"> -<h4 id="org8d1541d">General Registers</h4> -<div class="outline-text-4" id="text-org8d1541d"> +<div id="outline-container-org67926ce" class="outline-4"> +<h4 id="org67926ce">General Registers</h4> +<div class="outline-text-4" id="text-org67926ce"> <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-orgd61521c" class="outline-3"> -<h3 id="orgd61521c">Addressing and registers…again</h3> -<div class="outline-text-3" id="text-orgd61521c"> +<div id="outline-container-org824a260" class="outline-3"> +<h3 id="org824a260">Addressing and registers…again</h3> +<div class="outline-text-3" id="text-org824a260"> </div> -<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"> +<div id="outline-container-orgaa8f029" class="outline-4"> +<h4 id="orgaa8f029">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-orgaa8f029"> <p> Well lets take a step back to the notion of effective addresses VS relative ones. </p> </div> </div> -<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"> +<div id="outline-container-org85a2533" class="outline-4"> +<h4 id="org85a2533">Effective = 10h x Segment + Offset . Part1</h4> +<div class="outline-text-4" id="text-org85a2533"> <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="orga0fd499"></a>Answer :<br /> -<div class="outline-text-5" id="text-orga0fd499"> +<li><a id="orgae0f70c"></a>Answer :<br /> +<div class="outline-text-5" id="text-orgae0f70c"> <div class="org-src-container"> <pre class="src src-asm"><span style="color: #89b4fa;">MOV</span> [DS:0234h], 0x0005 </pre> @@ -159,7 +159,7 @@ Why ? Let’s break it down : -<div id="orge5d4a33" class="figure"> +<div id="orgd01a20f" class="figure"> <p><img src="../../src/gifs/lain-dance.gif" alt="lain-dance.gif" /> </p> </div> @@ -177,9 +177,9 @@ Simple, right ?, now for another example </li> </ul> </div> -<div id="outline-container-org93b46d0" class="outline-4"> -<h4 id="org93b46d0">Another example :</h4> -<div class="outline-text-4" id="text-org93b46d0"> +<div id="outline-container-org811633c" class="outline-4"> +<h4 id="org811633c">Another example :</h4> +<div class="outline-text-4" id="text-org811633c"> <p> What if we now have this instruction ? </p> @@ -192,9 +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-orgcba10b0" class="outline-4"> -<h4 id="orgcba10b0">Segment + Register <3</h4> -<div class="outline-text-4" id="text-orgcba10b0"> +<div id="outline-container-orge6219c5" class="outline-4"> +<h4 id="orge6219c5">Segment + Register <3</h4> +<div class="outline-text-4" id="text-orge6219c5"> <p> Consider <b>DS = 0100h</b> and <b>BX = BP = 0234h</b> and this code snippet: </p> @@ -230,8 +230,8 @@ The General rule of thumb is as follows : </ul> </div> <ul class="org-ul"> -<li><a id="orgf6c5f3b"></a>Note<br /> -<div class="outline-text-5" id="text-orgf6c5f3b"> +<li><a id="orga9c3a1b"></a>Note<br /> +<div class="outline-text-5" id="text-orga9c3a1b"> <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> @@ -249,7 +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 20:55</p> +<p class="date">Created: 2024-03-17 Sun 21:28</p> </div> </body> </html> |