Chapter 3.10, Problem 3.48PP

A.

Program Plan Intro

Load Effective Address:

• The load effective address instruction “leaq” is a variant of “movq” instruction.
• The instruction form reads memory to a register, but memory is not been referenced at all.
• The first operand of instruction is a memory reference; the effective address is been copied to destination.
• The pointers could be generated for later references of memory.
• The common arithmetic operations could be described compactly using this instruction.
• The operand in destination should be a register.

Data movement instructions:

• The different instructions are been grouped as “instruction classes”.
• The instructions in a class performs same operation but with different sizes of operand.
• The “Mov” class denotes data movement instructions that copy data from a source location to a destination.
• The class has 4 instructions that includes:
  • movb:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 1 byte data size.
  • movw: 
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 2 bytes data size.
  • movl:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 4 bytes data size.
  • movq:
    • It copies data from a source location to a destination.
    • It denotes an instruction that operates on 8 bytes data size.

Comparison Instruction:

• The “CMP” instruction sets condition code according to differences of their two operands.
• The working pattern is same as “SUB” instruction but it sets condition code without updating destinations.
• The zero flag is been set if two operands are equal.
• The ordering relations between operands could be determined using other flags.
• The “cmpl” instruction compares values that are double word.

Unary and Binary Operations:

• The details of unary operations includes:
  • The single operand functions as both source as well as destination.
  • It can either be a memory location or a register.
  • The instruction “incq” causes 8 byte element on stack top to be incremented.
  • The instruction “decq” causes 8 byte element on stack top to be decremented.
• The details of binary operations includes:
  • The first operand denotes the source.
  • The second operand works as both source as well as destination.
  • The first operand can either be an immediate value, memory location or register.
  • The second operand can either be a register or a memory location.

B.

Explanation of Solution

Rearranged ordering provides greater security:

• In protected code, the local variables “v” is placed closer to stack top than “buf”...