Contents
- 1 Are some instructions in x86-64 assembly redundant?
- 2 How many instructions are in x86?
- 3 What is the longest instruction in 8086?
- 4 How many bits is the RAX register?
- 5 Why is 8086 queue only six byte long?
- 6 What causes the Intel 80386 CPU to hang?
- 7 What is the Reference Manual for Intel 80386?
- 8 How many instructions are in the Intel 8086?
Are some instructions in x86-64 assembly redundant?
3 Answers. The x86 instruction set (16, 32 or 64 bit, all variants/modes) guarantees / requires that instructions are at most 15 bytes. Anything beyond that will give an “invalid opcode”. You can’t achieve that without using redundant prefixes (e.g. multiple 0x66 or 0x67 prefixes, for example).
How many instructions are in x86?
According to Intel’s XED, as of this writing, there are 1503 defined x86 instructions (“iclasses” in XED lingo), from AAA to XTEST (this includes AMD-specific extensions too, by the way).
How long is an x86 instruction?
between 1 and 15 bytes
x86 instructions can be anywhere between 1 and 15 bytes long. The length is defined separately for each instruction, depending on the available modes of operation of the instruction, the number of required operands and more.
What is the longest instruction in 8086?
8086 Queue is only Six Byte long: This is because the longest instruction in the instruction set of 8086 is six byte long. Hence with a six byte long queue it is possible to pre-fetch even the longest instruction in the main program.
How many bits is the RAX register?
64-bit
rax is the 64-bit, “long” size register. It was added in 2003 during the transition to 64-bit processors.
What size in bytes are opcodes on an x86 processor?
x86 Opcode Sizes The x86 opcode bytes are 8-bit equivalents of iii field that we discussed in simplified encoding. This provides for up to 512 different instruction classes, although the x86 does not yet use them all.
Why is 8086 queue only six byte long?
What causes the Intel 80386 CPU to hang?
Misaligned Selectors: If a 16-bit memory operand is loaded into a segment register, the 80386 hangs if the selector is not word-aligned. This can happen with a MOV instruction and with the LDS, LES, LFS, LGS, and LSS instructions. Testing Null Selectors: The 80386 hangs if an LAR, LSL, VERR, or VERW instruction is used to test a null selector.
How many instructions are in the x86 instruction set?
The x86 instruction set has been extended several times, introducing wider registers and datatypes as well as new functionality. Below is the full 8086/8088 instruction set of Intel (81 instructions total).
What is the Reference Manual for Intel 80386?
As the “INTEL 80386 PROGRAMMER’S REFERENCE MANUAL 1986”, section 10.1, explains: The contents of EAX depend upon the results of the power-up self test. The self-test may be requested externally by assertion of BUSY# at the end of RESET.
How many instructions are in the Intel 8086?
Below is the full 8086/8088 instruction set of Intel (81 instructions total). Most if not all of these instructions are available in 32-bit mode; they just operate on 32-bit registers ( eax, ebx, etc.) and values instead of their 16-bit ( ax, bx, etc.) counterparts. See also x86 assembly language for a quick tutorial for this processor family.