The primary example is the Intel X86 architecture. The Intel 8086 was, internally, a 16-bit processor: all of its registers were 16 bits wide. However, the address bus was 20 bits wide (1 MiB). This meant that you couldn’t hold an entire address in a register, limiting you to the first 64 kiB. Intel’s solution … Read more
According to this, they are the same: The shift arithmetic left (SAL) and shift logical left (SHL) instructions perform the same operation; they shift the bits in the destination operand to the left (toward more significant bit locations). For each shift count, the most significant bit of the destination operand is shifted into the CF … Read more
The physical address is calculated from 2 parts. i) segment address. ii) offset address. The CS(code segment register) is used to address the code segment of the memory i.e a location in the memory where the code is stored. The IP(Instruction pointer) contains the offset within the code segment of the memory. Hence CS:IP is … Read more
For-loops: For-loop in C: for(int x = 0; x<=3; x++) { //Do something! } The same loop in 8086 assembler: xor cx,cx ; cx-register is the counter, set to 0 loop1 nop ; Whatever you wanna do goes here, should not change cx inc cx ; Increment cmp cx,3 ; Compare cx to the limit … Read more
There are a lot of possibility how to mov 0 in to ax under IA32… lea eax, [0] mov eax, 0FFFF0000h //All constants form 0..0FFFFh << 16 shr ax, 16 //All constants form 16..31 shl eax, 16 //All constants form 16..31 And perhaps the most strange… 🙂 @movzx: movzx eax, byte ptr[@movzx + 6] //Because … Read more
In real mode to address the first full 1MiB of memory a mechanism called 20-bit segment:offset addressing is used. 0xb8000 is a physical memory address. You need to use something called a far pointer that allows you to address memory with real mode segmentation. The different types of pointers are described in this Stackoverflow Answer … Read more
You can use objdump. According to this article the syntax is: objdump -D -b binary -mi386 -Maddr16,data16 mbr