SHL

Table of Contents

1. SHL (shl)
   1. Basic function
   2. Instruction execution process
   3. Instruction format
   4. Behavioral characteristics
   5. Common uses

SHL (shl)

Basic function

SHL (Shift Logical Left) shifts the destination operand left by n bits, filling the right side with 0s.
In mathematical terms, it is equivalent to: dest = dest * 2^n。

Instruction execution process

• Shift left the specified number of times
• Fill the right side with 0s
• Update flags such as CF, ZF, SF, and OF
• The last bit shifted out → CF

Instruction format

1
shl r/m32, imm8
2
shl r/m64, imm8
3
shl r/m32, cl
4
shl r/m64, cl

Behavioral characteristics

• Logical operation; does not consider the sign
• Performs fast multiplication on values
• Has a strong effect on flags, especially CF and OF

Common uses

• Quickly multiply by 2^n
• Address calculation (such as structure base address offsets)
• Bitmap construction
• In ROP/shellcode, construct large numbers