From 9c369129fc44ce90088476387cd54665035a9505 Mon Sep 17 00:00:00 2001 From: Crystal Date: Sat, 24 Feb 2024 17:36:27 +0100 Subject: Add stuff --- blog/asm/1.html | 119 ++++++++++++++++++++++++++++++++++++++++++++ src/org/blog/assembly/1.org | 59 ++++++++++++++++++++++ 2 files changed, 178 insertions(+) create mode 100644 blog/asm/1.html create mode 100644 src/org/blog/assembly/1.org diff --git a/blog/asm/1.html b/blog/asm/1.html new file mode 100644 index 0000000..e9efd34 --- /dev/null +++ b/blog/asm/1.html @@ -0,0 +1,119 @@ + + + + + + + +x86 Assembly from my understanding + + + + + + + +
+ UP + | + HOME +
+

x86 Assembly from my understanding

+

+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 +

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+

Memory :

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+

+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) +

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  • 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.
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+The offset and segment are encoded in 16bits, so they take a value between 0 and 65535 +

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Important :

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+

+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. +

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  • Example :
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    +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 : 212 = 4096 different ways !!! +

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Registers

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+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). +

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General Registers

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+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: +

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ADD AX, AX ;(AX = AX + AX)
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+
+ +

+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: +

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+
MOV BL, [500] ;(BL = 500H)
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Author: Crystal

+

Created: 2024-02-24 Sat 17:36

+
+ + 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: +#+HTML_HEAD: +#+OPTIONS: html-style:nil +#+OPTIONS: toc:nil +#+HTML_HEAD: +#+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 -- cgit 1.4.1-2-gfad0