Tutorial How to write an 8 byte MOV instruction

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Have you ever had the issue of needing to move something bigger than 65535 into R0, and you needed to use a literal number (MOV R0, #255) instead of a register (MOV R0, R7)? Well I did to make a custom floating point return value to separate the field of view function for Bullet Force so I would still be able to get the zoomed in field of view when I aim down sights.

 

This is a very good when you want to move a floating point value into R0, like 1120403456. Additionally, I'll use 1120403456 for this tutorial.

 

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Step 1:

Convert your number to hexadecimal. Go to http://www.binaryhexconverter.com/decimal-to-hex-converter.

 

1120403456 is 42C80000 in hexadecimal. Cool.

 

Step 2:

Break your hexadecimal value in half, and that will leave you with two "sections". For 42C80000:

 

The first section would be 0000.

The second section would be 42C8.

 

Step 3

Use ARM Converter (http://armconverter.com) to generate the instructions we need. They will always be in this format:

 

MOVW R0, #/*section 1*/
MOVT R0, #/*section 2*/

In my case, my instructions would be:

 

MOVW R0, #0x0000
MOVT R0, #0x42C8

Convert those two instructions, and write the hex down somewhere.

 

Step 4:

Time to make the hex string!

 

I used ARM Converter to convert these and it gave me these hexes:

 

MOVW R0, #0x0000 = 40F20000

MOVT R0, #0x42C8 = C4F2C820

 

Combine the two, and the final hex of MOV R0, #0x42C80000 is:

40F20000C4F2C820

Keep in mind this is 8 bytes, so you'll need to find 4 bytes of extra space before the instruction you are overwriting is.

[Patricktph 36.7k 10.2.1]

@@shmoo

 

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