Jul 28, 2019 · I want to know how to properly do it, because the way I'm doing it isn't working. When setting the BP register with 7C00h, then setting the SP register with BP, then pushing some ASCII, then getti...

x86 memory segmentation is a term for the kind of memory segmentation characteristic of the Intel x86 computer instruction set architecture. The x86 architecture has supported memory segmentation since the original Intel 8086 (1978), but x86 memory segmentation is a plainly descriptive retronym.

In x86 the registers bx and bp are totally unrelated. The only common thing about them is the word base. bx (base index) is a general-purpose register (like ax, cx and dx), typically used as a pointer to data (used for arrays and such)

Nov 1, 2011 · ds:si and es:di mean the segment:offset referred to by the registers in question. This is primarily important when you're working in real mode (where offsets are a maximum of 64K apiece). In real mode, the segment and offset are combined as segment * 16 + offset.

In our project, the bootloader is working in real mode (16 bits). Bootloader code is loaded by BIOS, so it did not have %ds, %ss, %sp setup properly when it is loaded. In bootloader, all the code and data share the same 512 bytes. So data will have the same segment as code.

1. Push old %bp + set %bp = %sp 2. Allocate space for local variables 3. Push callee-save regs if necessary %sp %sp + 4 temp var. 1 (temp var. n …) callee-save reg 1 (callee-save regs) (local var. n …) local var. 1 old %ebp return address function arg. 1 (function arg. n …)... %bp %bp - 4 %bp + 4 %bp + 8 14

Contract between caller and callee on x86: Functions can do anything that doesn't violate contract. By convention, GCC does more: Assembler takes assembly language (ASCII text), produces .o file (binary, machine-readable!) only implemented in software rather than hardware!

Dec 1, 2015 · Yes, all addresses are relative to the chosen segment - ds in most cases, ss if you use bp, and the given register if you use an explicit override prefix. Note there wasn't a way to index relative to sp in 16 bit mode, and bp, if used at all, was always the first register in R1+R2 combinations, forcing ss to be used with bp.

Dec 7, 2023 · When using x86 assembly, it is important to consider the differences between architectures that are 16, 32, and 64 bits. This page will talk about some of the basic differences between architectures with different bit widths.

Dec 31, 2020 · Then bp is set to 78h. 78h is 4 times 1Eh. That means the lds si loads a far pointer at dword [0:78h] into the ds:si register pair. 0:78h is where the interrupt vector for interrupt 1Eh lives. This happens to be used as a pointer to a DPT .