X86 Accumulation Apparatus Accent About-face
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25 July 17:51
x86 accumulation instructions accept a one-to-one accord with the basal apparatus instructions. This agency that about we can catechumen accumulation instructions into apparatus instructions with a look-up table. This page will allocution about some of the conversions from accumulation accent to apparatus language.
The x86 architectonics is a circuitous apprenticeship set computer (CISC) architecture. Amidst additional things, this agency that the instructions for the x86 architectonics are of capricious lengths. This can create the processes of assembly, disassembly and apprenticeship adaptation added complicated, because the apprenticeship breadth needs to be affected for anniversary instruction.
x86 instructions can be anywhere amid 1 and 15 bytes long. The breadth is authentic alone for anniversary instruction, depending on the accessible modes of operation of the instruction, the amount of appropriate operands and more.
This is the accepted apprenticeship anatomy for the 8086:
;Prefixes: Alternative prefixes which change the operation of the instruction
;Opcode: the opcode is a 6 bit abundance that determines what apprenticeship ancestors the cipher is
;D: (1 bit) Direction. 1 = Annals is Destination, 0 = Annals is source.
;W: (1 bit) Operation size. 1 = Word, 0 = byte.
;MOD: (2 bits) Annals mode.
;Reg: (3 bits) Register. Anniversary annals has an identifier.
;R/M: (3 bits) Register/Memory operand
After the antecedent 2 bytes, anniversary apprenticeship can accept some added addressing/immediate data bytes.
Lets construe the afterward apprenticeship into bytecode:
XOR CL, [12H]
The opcode for XOR is 001100. D is 1 because the CL annals is the destination. W is 0 because we accept a byte of data. Our first byte accordingly 00110010.
Now, we understand that the cipher for CL is 001. Reg appropriately has the amount 001. The abode is defined as a simple displacement, so the MOD amount is 00 and the R/M is 110. Byte 2 is appropriately 00001110.
Byte 3 contains the actual data - 12H, or (00010010b)
All together,
XOR CL, [12H] = 00110010 00001110 00010010 = 320E12H
The 32-bit instructions are encoded in a actual agnate way to the 16-bit instructions, except (by default) they act aloft dword quantities rather than words. Also, they abutment a abundant added adjustable anamnesis acclamation format, which is create accessible by the accession of an SIB scale-index-base byte, which follows the ModR/M byte.
x86 accumulation instructions accept a one-to-one accord with the basal apparatus instructions. This agency that about we can catechumen accumulation instructions into apparatus instructions with a look-up table. This page will allocution about some of the conversions from accumulation accent to apparatus language.
The x86 architectonics is a circuitous apprenticeship set computer (CISC) architecture. Amidst additional things, this agency that the instructions for the x86 architectonics are of capricious lengths. This can create the processes of assembly, disassembly and apprenticeship adaptation added complicated, because the apprenticeship breadth needs to be affected for anniversary instruction.
x86 instructions can be anywhere amid 1 and 15 bytes long. The breadth is authentic alone for anniversary instruction, depending on the accessible modes of operation of the instruction, the amount of appropriate operands and more.
This is the accepted apprenticeship anatomy for the 8086:
;Prefixes: Alternative prefixes which change the operation of the instruction
;Opcode: the opcode is a 6 bit abundance that determines what apprenticeship ancestors the cipher is
;D: (1 bit) Direction. 1 = Annals is Destination, 0 = Annals is source.
;W: (1 bit) Operation size. 1 = Word, 0 = byte.
;MOD: (2 bits) Annals mode.
;Reg: (3 bits) Register. Anniversary annals has an identifier.
;R/M: (3 bits) Register/Memory operand
After the antecedent 2 bytes, anniversary apprenticeship can accept some added addressing/immediate data bytes.
Lets construe the afterward apprenticeship into bytecode:
XOR CL, [12H]
The opcode for XOR is 001100. D is 1 because the CL annals is the destination. W is 0 because we accept a byte of data. Our first byte accordingly 00110010.
Now, we understand that the cipher for CL is 001. Reg appropriately has the amount 001. The abode is defined as a simple displacement, so the MOD amount is 00 and the R/M is 110. Byte 2 is appropriately 00001110.
Byte 3 contains the actual data - 12H, or (00010010b)
All together,
XOR CL, [12H] = 00110010 00001110 00010010 = 320E12H
The 32-bit instructions are encoded in a actual agnate way to the 16-bit instructions, except (by default) they act aloft dword quantities rather than words. Also, they abutment a abundant added adjustable anamnesis acclamation format, which is create accessible by the accession of an SIB scale-index-base byte, which follows the ModR/M byte.
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