Intel 64 and IA-32 Architectures Software Developers Manual Volume 2B, Instruction Set Reference, N-Z

4-344 Vol. 2B
INSTRUCTION SET REFERENCE, N-Z
Description
Subtracts the second operand (source operand) from the first operand (destination
operand) and stores the result in the destination operand. The destination operand
can be a register or a memory location; the source operand can be an immediate,
register, or memory location. (However, two memory operands cannot be used in one
instruction.) When an immediate value is used as an operand, it is sign-extended to
the length of the destination operand format.
The SUB instruction performs integer subtraction. It evaluates the result for both
signed and unsigned integer operands and sets the OF and CF flags to indicate an
overflow in the signed or unsigned result, respectively. The SF flag indicates the sign
of the signed result.
In 64-bit mode, the instruction’s default operation size is 32 bits. Using a REX prefix
in the form of REX.R permits access to additional registers (R8-R15). Using a REX
prefix in the form of REX.W promotes operation to 64 bits. See the summary chart at
the beginning of this section for encoding data and limits.
This instruction can be used with a LOCK prefix to allow the instruction to be
executed atomically.
Operation
DEST ← (DEST – SRC);
Flags Affected
The OF, SF, ZF, AF, PF, and CF flags are set according to the result.
Protected Mode Exceptions
#GP(0) If the destination is located in a non-writable segment.
If a memory operand effective address is outside the CS, DS,
ES, FS, or GS segment limit.
If the DS, ES, FS, or GS register contains a NULL segment
selector.
#SS(0) If a memory operand effective address is outside the SS
segment limit.
#PF(fault-code) If a page fault occurs.
#AC(0) If alignment checking is enabled and an unaligned memory
reference is made while the current privilege level is 3.
Real-Address Mode Exceptions
#GP If a memory operand effective address is outside the CS, DS,
ES, FS, or GS segment limit.
#SS If a memory operand effective address is outside the SS
segment limit.