X86 Assembly Language - Instruction Types

Instruction Types

In general, the features of the modern x86 instruction set are:

  • A compact encoding
    • Variable length and alignment independent (encoded as little endian, as is all data in the x86 architecture)
    • Mainly one-address and two-address instructions, that is to say, the first operand is also the destination.
    • Memory operands as both source and destination are supported (frequently used to read/write stack elements addressed using small immediate offsets).
    • Both general and implicit register usage; although all seven (counting ebp) general registers in 32-bit mode, and all fifteen (counting rbp) general registers in 64-bit mode, can be freely used as accumulators or for addressing, most of them are also implicitly used by certain (more or less) special instructions; affected registers must therefore be temporarily preserved (normally stacked), if active during such instruction sequences.
  • Produces conditional flags implicitly through most integer ALU instructions.
  • Supports various addressing modes including immediate, offset, and scaled index but not PC-relative, except jumps (introduced as an improvement in the x86-64 architecture).
  • Includes floating point to a stack of registers.
  • Contains special support for atomic read-modify-write instructions (xchg, cmpxchg/cmpxchg8b, xadd, and integer instructions which combine with the lock prefix)
  • SIMD instructions (instructions which perform parallel simultaneous single instructions on many operands encoded in adjacent cells of wider registers).

Read more about this topic:  X86 Assembly Language

Famous quotes containing the words instruction and/or types:

    “Much of the pressure contemporary parents feel with respect to dressing children in designer clothes, teaching young children academics, and giving them instruction in sports derives directly from our need to use our children to impress others with our economic surplus. We find “good” rather than real reasons for letting our children go along with the crowd.”
    —David Elkind (20th century)

    “Our children evaluate themselves based on the opinions we have of them. When we use harsh words, biting comments, and a sarcastic tone of voice, we plant the seeds of self-doubt in their developing minds.... Children who receive a steady diet of these types of messages end up feeling powerless, inadequate, and unimportant. They start to believe that they are bad, and that they can never do enough.”
    —Stephanie Martson (20th century)