Comparing Strings in Assembly Part 2

Posted on August 19, 2011 by sean • Posted in Linux, Programming • Tagged 64-bit, addl, addq, as, assembling, assembly, assembly primer for hackers, buffer, cmp, cmpsb, cmpstr, compare, data, df, df flag, functions, gas, hackers, hacking, int, leal, linx, loopz, movb, movl, movq, oscp, pentesting with backtrack, pointer, pointers, popq, pushq, registers, stack, string, strings, sub, text, x86 • Leave a comment

Earlier today I wrote some assembly code to compare 2 strings and print out whether or not they were equal to one another. I’ve been learning more assembly and so I thought I would tweak it a bit to improve the way it works and add more “features”. After some studying I’ve managed to get it working as a real function that actually takes arguments via the stack. On top of that, the function now returns a value that designates the index where the comparison failed; this is stored in the EAX register. Even further, by using a buffer in memory I was able to print a string that informs the user of the index where the comparison failed.

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Data Types and Moving Data in Assembly

Posted on August 19, 2011 by sean • Posted in Linux, Programming, Security • Tagged as, assembling, assembly, assembly primer for hackers, bss, data, data types, debugging, df, df flag, gas, gdb, hackers, hacking, heap, linux, lods, memory, mov, movb, moving, movl, movs, movw, oscp, pentesting with backtrack, pointer, pointers, registers, stack, stos, text, vivek ramachandran, x86 • Leave a comment

I’m still following the Assembly Primer for Hackers from Vivek Ramachandran of SecurityTube in preparation for Penetration Testing with BackTrack. In this review I’ll cover data types and how to move bytes, numbers, pointers and strings between labels and registers.

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