parsing assembly code in perl.

Question

0000000000033a1b subq $0x28,%rsp

I am having trouble extracting 0x28 from the above line. I am able to extract subq from a big list of assembly code but i only want 0x28 since this gives me the stack size. I was thinking of using substr() function buy there are variations to it, another one could look like this:

0000000000033a1c subq $0x000000b8,%rsp

in this case i only want 0x000000b8.

I am using perl.

Thank you.

Answer 1

If your input of the following format always:

instruction_address operand $stack_size,register

you can do:

$a = '0000000000033a1b subq $0x28,%rsp';
$a =~s/^.*?\$(.*?),.*$/\1/;
print $a; # prints 0x28

Answer 2

Without code, my guess is that you're not escaping the dollar sign. Thus you are asking for it to match the end of the line, and then '0x28'.

In any regex, /\$0x(\p{XDigit}+)/ should capture '28' out of that string.