Intel manual format

September 4, 2015 ยท View on GitHub

How the Intel manual documents the instruction encodings.

  • Opcode
  • Instruction
  • Op / En
  • 64-Bit Mode
  • Compat / Leg Mode
  • CPUID feature flag
  • Description

They are explained in section 3.1.

Instruction

E.g.:

XCHG EAX, r32

Means: takes 2 arguments:

  • EAX: TODO
  • r32: a 32-bit register

Other important values:

  • r/m32: either a 32-bit register or RAM Memory
  • imm32: value directly encoded on memory

Op/En

Operand Encoding

Refers to an entry on the "Instruction Operand Encoding" table.

Every instruction has it's own "Instruction Operand Encoding" table.

TODO understand an operand encoding table, e.g. for mov.

CPUID feature flag

Which version of CPU support the feature as reported by CPUID.

Compat / Leg Mode

  • valid
  • invalid: can be encoded, but generates an exception
  • N.E.: not encodable

64-bit mode

  • V: Supported.
  • I: Not supported.
  • N.E.: instruction syntax is not encodable in 64-bit mode (it may represent part of a sequence of valid instructions in other modes).
  • N.P.: REX prefix does not affect the legacy instruction in 64-bit mode.
  • N.I.: opcode is treated as a new instruction in 64-bit mode.
  • N.S.: requires an address override prefix in 64-bit mode and is not supported. Using an address override prefix in 64-bit mode may result in model-specific execution behavior