92 lines
2.4 KiB
Markdown
92 lines
2.4 KiB
Markdown
---
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search:
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exclude: true
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---
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# Assembly x86_64 - Math operations
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## Assembly Code
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We're going to use vim to write our code
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[ 192.168.0.18/24 ] [ /dev/pts/88 ] [~/binexp/asm]
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→ vim 5.asm
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section .data
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digit db 0, 10
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section .text
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global _start
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_start:
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mov rbx, 48 ;48 in the ASCII chart is the "0" character
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call _printRAX ;print "0" + 1
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call _printRAX ;print "1" + 1
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call _printRAX ;print "2" + 1
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call _printRAX ;print "3" + 1
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call _printRAX ;print "4" + 1
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mov rax, 60
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mov rdi, 0
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syscall
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_printRAX:
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add rbx, 1 ; we increment rbx by 1 (48, 49, 50, 51, ...)
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mov [digit], rbx ; we move the current value of rbx into the 'digit' memory address
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mov rax, 1 ; we use the syscall ID 1
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mov rdi, 1 ; we set the first arg to 1
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mov rsi, digit ; the second arg is set to be our 'digit' memory address
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mov rdx, 2 ; the third arg is the length of 2 bytes (let's not forget the newline char which is the '10' above)
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syscall
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ret
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Now let's check what's new in the code:
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mov [digit], rbx
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Here we are moving the rbx register into the memory address that's referenced by the 'digit' label.
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mov rbx, 48
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add rbx, 1
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mov [digit], rbx
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Now first we set the value of rbx to be 48, which is the "0" character in ascii. Then we want to add the value 1 to the value stored in rbx. and then we just move the rbx value into the memory address referenced by the 'digit' label
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Basically our code should print the character 1, 2, 3, 4 and 5
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## Compiling
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Here we're going to use nasm to compile our assembly code:
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[ 192.168.0.18/24 ] [ /dev/pts/89 ] [~/binexp/asm]
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→ nasm -f elf64 5.asm -o 5.o
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[ 192.168.0.18/24 ] [ /dev/pts/89 ] [~/binexp/asm]
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→ ld 5.o -o 5
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[ 192.168.0.18/24 ] [ /dev/pts/89 ] [~/binexp/asm]
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→ ./5
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12345%
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And that's it ! next tutorial we'll look into loops, you can click [here](6.md).
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