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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.
Instructions to load both extended segment register and general-purpose register at once, similar to 8086's LDS and LES instructions MOV DS2,r16,m32: 0F 3E /r: DS2: 63: Segment-override prefixes for the DS2 and DS3 extended segments. DS3: D6: IRAM: F1: Register File Override Prefix. Will cause memory operands to index into register file rather ...
Finally, the AVRtiny core deletes the 2-word LDS and STS instructions for direct RAM addressing, and instead uses the opcode space previously assigned to the load/store with displacement instructions for new 1-word LDS and STS instructions which can access the first 128 locations of general-purpose RAM, addresses 0x40 to 0xBF.
The VIA/Zhaoxin PadLock instructions are instructions designed to apply cryptographic primitives in bulk, similar to the 8086 repeated string instructions. As such, unless otherwise specified, they take, as applicable, pointers to source data in ES:rSI and destination data in ES:rDI, and a data-size or count in rCX.
In real mode, code may also modify the CS register by making a far jump (or using an undocumented POP CS instruction on the 8086 or 8088). [4] Of course, in real mode, there are no privilege levels; all programs have absolute unchecked access to all of memory and all CPU instructions.
The REX prefix provides additional space for encoding 64-bit addressing modes and additional registers present in the x86-64 architecture. Bit-field W changes the operand size to 64 bits, R expands reg to 4 bits, B expands r/m (or opreg in the few opcodes that encode the register in the 3 lowest opcode bits, such as "POP reg"), and X and B expand index and base in the SIB byte.
Reading and writing to these registers is handled by the rdmsr and wrmsr instructions, respectively. As these are privileged instructions, they can be executed only by the operating system. Use of the Linux msr kernel module creates a pseudo file "/dev/cpu/ x /msr" (with a unique x for each processor or processor core).
To save a value to the stack, the PUSH instruction is used. To retrieve a value from the stack, the POP instruction is used. Example: Assuming that SS = 1000h and SP = 0xF820. This means that current stack top is the physical address 0x1F820 (this is due to memory segmentation in 8086). The next two machine instructions of the program are: