One of my favorite hobbies is Reverse Engineering. It requires a solid knowledge of assembly and the use of disassemblers/debuggers to walk through compiled code. This allows you to alter, understand and reverse compiled programs. Each new program is like a puzzle waiting to be solved! For example, a lot of people reverse games like … Read more
Summary: NASM/YASM requires word [ecx] when the operand-size isn’t implied by the other operand. (Otherwise [ecx] is ok). MASM/TASM requires word ptr [ecx] when the operand-size isn’t implied by the other operand. (Otherwise [ecx] is ok). They each choke on the other’s syntax. WARNING: This is very strange area without any ISO standards or easy-to-find … Read more
Back in the “old days” when performance was always a concern, it made more sense. It was used in communication to verify integrity (do error checking) and a substantial portion of communication was serial, which makes more use of parity than parallel communications. In any case, it was trivial for the CPU to compute it … Read more
Could somebody please help me understand how CMOV improves branching? Well, it does NOT improve branching, it removes it. A CMOV could be seen as two instructions in one, a MOV and a NOP. Which one is executed depends on the flags. So internally it may look like if (cond) { mov dst, src } … Read more
From the nasm documentation: The SECTION directive (SEGMENT is an exactly equivalent synonym) Nasm can produce output in various formats, some of which support sections. Certain section names can be arbitrary (such as the three you listed), for them only the section flags count. The predefined ones are just convenience shortcuts, .text is marked as … Read more
Have you tried int 21h service 2? DL is the character to print. mov dl,’A’ ; print ‘A’ mov ah,2 int 21h To print the integer value, you’ll have to write a loop to decompose the integer to individual characters. If you’re okay with printing the value in hex, this is pretty trivial. If you … Read more
The memory barriers present on the x86 architecture – but this is true in general – not only guarantee that all the previous1 loads, or stores, are completed before any subsequent load or store is executed – they also guarantee that the stores have became globally visible. By globally visible it is meant that other … Read more
“H” for “Hexadecimal”, base 16. 0009H = 9 decimal, 000AH = 10 decimal, 000FH = 15 decimal, 0010H = 16, 0020H = 32 et cetera.
I think everyone is giving you the same answer. Instruction set is is the set (as in math) of all instructions the processor can execute or understand. Assembly language is a programming language. Let me try some examples based on some of the questions you are asking. And I am going to be jumping around … Read more
Addition and subtraction are the same, as is the low-half of a multiply. A full multiply, however, is not. Simple example: In 32-bit twos-complement, -1 has the same representation as the unsigned quantity 2**32 – 1. However: -1 * -1 = +1 (2**32 – 1) * (2**32 – 1) = (2**64 – 2**33 + 1) … Read more