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Below is the full 8086/8088 instruction set of Intel (81 instructions total). [2] These instructions are also available in 32-bit mode, in which they operate on 32-bit registers (eax, ebx, etc.) and values instead of their 16-bit (ax, bx, etc.) counterparts.
INT is an assembly language instruction for x86 processors that generates a software interrupt. It takes the interrupt number formatted as a byte value. [1] When written in assembly language, the instruction is written like this: INT X. where X is the software interrupt that should be generated (0-255).
; The 'enter' instruction can also do something similar); sub esp, 12 : 'enter' instruction could do this for us; mov [ebp-4], 3 : or mov [esp+8], 3; mov [ebp-8], 2 : or mov [esp+4], 2; mov [ebp-12], 1 : or mov [esp], 1 push 3 push 2 push 1 call callee; call subroutine 'callee' add esp, 12; remove call arguments from frame add eax, 5; modify ...
x86 assembly language is a family of low-level programming languages that are used to produce object code for the x86 class of processors. These languages provide backward compatibility with CPUs dating back to the Intel 8008 microprocessor, introduced in April 1972.
Furthermore, on a modern x86 system, BIOS calls can only be performed in Real mode, or Virtual 8086 mode. v8086 is not an option in Long mode. This means that a modern operating system, which operates in Protected mode (32 bit), or Long mode (64 bit), would need to switch into real mode and back to call the BIOS - a hugely expensive operation.
This is rarely a feature in a higher-level language, and so wrapper functions for system calls are written using inline assembler. The following C code example shows an x86 system call wrapper in AT&T assembler syntax, using the GNU Assembler. Such calls are normally written with the aid of macros; the full code is included for clarity.
Originally all System/360 operating systems were written in assembler language, and all system interfaces were defined by macro definitions. Access from high-level languages (HLLs) was restricted to what that language supplied, and other system calls had to be coded as assembler subroutines called from HLL programs.
In the x86 computer architecture, HLT (halt) is an assembly language instruction which halts the central processing unit (CPU) until the next external interrupt is fired. [1] Interrupts are signals sent by hardware devices to the CPU alerting it that an event occurred to which it should react.