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There is a structure with size of 16-Bytes, and an array of it is defined. The disassembly code for navigation through the array is:

MOV     i, i,LSL#4
LDR     R4, =arr_of_struct 
ADD     i, i, R4
LDR     var, [i] 

But the decompiled code is:

var = arr_of_struct[4 * i];

Which is wrong and should be:

var = arr_of_struct[4 * i].field_0;

I think the problem is in first line of disassembly MOV i, i,LSL#4. Obviously it is multiplying the array index by 16 which is the size of my struct. But IDA translated this line to [4 * i] !!!

So the first question is what's the reason of this behavior in IDA? And the second is how can I fix this?

EDIT: More information:

enter image description here

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  • 2
    Which version of IDA and decompiler do you use?
    – Robert
    Apr 17, 2023 at 9:04
  • 1
    IDA version 7.6 SP1, Decompiler ver 7.6.0.210427
    – E.A
    Apr 17, 2023 at 11:34
  • 2
    You'll need to show more of the decompiler output. One line is not sufficient. Apr 17, 2023 at 14:01

1 Answer 1

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I found the solution for this issue, and post it here hope help someone someday...

I undefined the "arr_of_struct" (Ctrl+U), undefined both the array and also the structure variable:

enter description here ====> enter image description here

The output changed to deal with the undefined variable:

enter image description here

Declare struct variable again (Alt+Q), and define its location as an array (Pressing *), and the output changed to the right and expected shape:

enter image description here

Now I know how to fix it, but the first question is still remains:

What's the reason of this behavior in IDA? Is there a sequence needed to consider while defining array of structures?

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