The first is equate, similar to C’s: #define len 2 in that it doesn’t actually allocate any space in the final code, it simply sets the len symbol to be equal to 2. Then, when you use len later on in your source code, it’s the same as if you’re using the constant 2. The … Read more
IACA Analysis Using IACA (the Intel Architecture Code Analyzer) reveals that macro-op fusion is indeed occurring, and that it is not the problem. It is Mysticial who is correct: The problem is that the store isn’t using Port 7 at all. IACA reports the following: Intel(R) Architecture Code Analyzer Version – 2.1 Analyzed File – … Read more
Section 2.2 of the NASM documentation is titled Quick Start for MASM Users which lists the important differences between NASM and MASM. NASM version 2.15 added some MASM compatibility, including a %use masm macro package. See section 6.5 masm: MASM compatibility. Even without the macro package, ? and DUP work in data directives like db, … Read more
NASM actually uses its own variation of Intel syntax, different from the MASM syntax used in Intel’s official documentation. The opcode names and operand orders are the same as in Intel so the instructions look the same at first glance, but any significant program will have differences. For example with MASM the instruction used by … Read more
ORG is used to set the assembler location counter. This may or may not translate to a load address at link time. It can be used to define absolute addresses, e.g. when defining something like interrupt vectors which may need to be at a fixed address, or it can be used to introduce padding or … Read more
[L1] means the memory contents at address L1. After running mov al, [L1] here, The al register will receive the byte at address L1 (the letter ‘w’).
I learned from Kip Irvine’s book. If you ignore the (fair) criticisms of his (irrelevant) libraries, I can recommend it as a good introduction to the language itself — although for the really interesting stuff you have to hunt out obsessives on the net. I think it’s useful to understand what happens at the lower … Read more
This example shows how to go directly to the Windows API and not link in the C Standard Library. global _main extern _GetStdHandle@4 extern _WriteFile@20 extern _ExitProcess@4 section .text _main: ; DWORD bytes; mov ebp, esp sub esp, 4 ; hStdOut = GetstdHandle( STD_OUTPUT_HANDLE) push -11 call _GetStdHandle@4 mov ebx, eax ; WriteFile( hstdOut, message, … Read more