Declaring Arrays In x86 Assembly

Question

I am learning Assembly and I need to make a large array. I have looked around at how to declare arrays and I have come across this.

array db 10 dup(?)

Where an array of 10 uninitialized bytes is declared. I tried this and tried to assemble it and get "error: comma expected after operand 1". I realized that the '?' is not supported in x86 so I made it a constant and got the same error. I ended up doing this.

array db 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

This worked! But the problem is, I need large arrays (~100-400 integers) and their values will not always be known. I could write out 400 0's but I figured there must be an easier way. So is there a better way to declare large arrays?

I am using x86_64 Assembly on an Intel-Based Macbook Pro with AT&T syntax.

Solution 1

Did you try TIMES directive.Use this code for declaring an array of a given size.

array TIMES 8 DB 0

This will create an array of size 8

Refer to this link for more.

Solution 2

The AT&T syntax is used by the GNU assembler. The directive you're looking for is .fill <count>\[, <data-size>\[, <value>\]\]. In the specific case of 400 bytes:

array:  .fill  400

data-size defaults to 1 (byte). I believe the value that fills the 400 bytes defaults to zero.

---

nasm

times

predefine

.text

.data

.bss

nasm

resb

       setion .bss
       ...
arr1   resb  400             ; Reserve 400 bytes (uninitialized)
arr2   times 400 resb 1      ;  Same thing, using times

Comments

[Weather Vane]

Yes the dup is MASM.

[Peter Cordes]

This is MASM syntax. Tested in NASM version 2.14.02, and as expected I get an error: error: comma expected after operand 1.