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
[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’).
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
According to the x86 ABI, EBX, ESI, EDI, and EBP are callee-save registers and EAX, ECX and EDX are caller-save registers. It means that functions can freely use and destroy previous values EAX, ECX, and EDX. For that reason, save values of EAX, ECX, EDX before calling functions if you don’t want their values to … Read more
On modern Linux systems, the linker will mark stack/data non-executable IFF all objects that participate in the link have a special “marker” section .note.GNU-stack. If you compile e.g. int foo() { return 1; } into assembly (with gcc -S foo.c), you’ll see this: .section .note.GNU-stack,””,@progbits For nasm, the syntax is shown in section 8.9.2 of … Read more