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iakovlev.org
Материал взят на персональной странице Jim Plusquellic , профессора Питтсбургского университета

Intel Assembly

  • Формат инструкций:

 

  • LABEL:
    • Метка хранит символическое имя адреса памяти .

 

  • OPCODE:
    • Собственно сама инструкция.

 

  • OPERANDS:
    • Значение регистра , адреса памяти или непосредственно само значение .

 

    • Операндов может быть от 0 до 3 .

Data Addressing Modes

  • Инструкции перемещения данных (bytes, words , doublewords) либо между регистрами либо между регистрами и памятью .

 

  • Это команда movs которая обменивает данные находящиеся в памяти .

 

  • В большинстве своем инструкции по перемещению данных не изменяют регистр EFLAGS .

 

  • Format:
    • opcode destination , source

 

 

  • Register

Data Addressing Modes

  • Immediate

 

  • Direct (eax), Displacement (other regs)

 

  • Register Indirect
      • Any of eax , ebx , ecx , edx , ebp , edi or esi may be used.

Data Addressing Modes

  • Base-plus-index
      • Any combination of eax , ebx , ecx , edx , ebp , edi or esi .

 

  • Register relative
      • A second variation includes: mov eax , [ ARR+ ebx ]

Data Addressing Modes

  • Base relative-plus-index
      • A second variation includes: mov eax , [ ebx + edi +4]

 

  • Scaled-index
      • A second variation includes: mov eax , ebx *2+ ecx +offset
      • Scaling factors can be 2X, 4X or 8X.

Data Addressing Modes

  • Register addressing:
  • Note: mov really COPIES data from the source to destination register.
  • Never mix an 16-bit register with a 32-bit, etc.
      • For example
  • None of the mov instruction effect the EFLAGS register.

Data Addressing Modes

  • Immediate addressing:
    • The value of the operand is given as a constant in the instruction stream.
  • Use b for binary, q for octal and nothing for decimal.

 

  • ASCII data requires a set of apostrophes:

 

  • Register and immediate addressing example:

Data Addressing Modes

  • Direct addressing:
    • Transfers between memory and al , ax and eax .
      • Usually encoded in 3 bytes, sometime 4:

 

  • Displacement:
    • Displacement instructions are encoded with up to 7 bytes (32 bit register and a 32 bit displacement).

Data Addressing Modes

  • Direct and displacement addressing example:
    • Note: Direct addressing (using al) requires 3 bytes to encode while Displacement (using bx) requires 4.

 

  • Register Indirect addressing:
    • Offset stored in a register is added to the segment register.
    • The memory to memory mov is allowed with string instructions.

Data Addressing Modes

  • Register Indirect addressing (cont)
    • Any register EXCEPT esp for the 80386 and up.
      • For eax , ebx , ecx , edx , edi and esi : The data segment is the default.
      • For ebp : The stack segment is the default.

 

    • Some versions of register indirect require special assembler directives byte, word , or dword
    • Does [ edi ] address a byte, a word or a double-word?

 

    • The assembler can't determine the size of 0x10 !
      • Use:

Data Addressing Modes

  • Base-Plus-Index addressing:
    • Effective address computed as:
      • seg_base + base + index.

 

    • Base registers: Holds starting location of an array.
  • ebp (stack)
  • ebx (data)
  • Any 32-bit register except esp.

 

    • Index registers: Holds offset location.
  • edi
  • esi
  • Any 32-bit register except esp .

Data Addressing Modes

  • Base-Plus-Index addressing:

Data Addressing Modes

  • Register Relative addressing:
    • Effective address computed as:
      • seg_base + base + constant.
    • Same default segment rules apply with respect to ebp , ebx , edi and esi .
      • Displacement constant is any 32-bit signed value.

 

  • Base Relative-Plus-Index addressing:
    • Effective address computed as:
      • seg_base + base + index + constant.
    • Designed to be used as a mechanism to address a two-dimensional array.

Data Addressing Modes

  • Base Relative-Plus-Index addressing:

Data/Code Addressing Modes

  • Scaled-Index addressing:
    • Effective address computed as:
      • seg_base + base + constant*index.

 

Code Memory-Addressing Modes:

  • Used in jmp and call instructions.
    • Three forms:
  • Direct
  • PC-Relative
  • Indirect

 

    • Direct:
      • Absolute jump address is stored in the instruction following the opcode.

Code Addressing Modes

    • An inter segment jump:
    • This far jmp instruction loads cs with 1000H and eip with 00000000H.
      • A far call instruction is similar.

 

  • PC-Relative:
    • A displacement is added to the EIP register.
    • This constant is encoded into the instruction itself, as above.

 

    • Intra segment jumps:
  • Short jumps use a 1-byte signed displacement.
  • Near jumps use a 4-byte signed displacement.
    • The assembler usually computes the displacement and selects the appropriate form.

Code Addressing Modes

  • Indirect:
    • Jump location is specified by a register.
    • There are three forms:
  • Register:
      • Any register can be used: eax , ebx , ecx , edx , esp , ebp , edi or esi .

 

  • Register Indirect:
      • Intra segment jumps can also be stored in the data segment.

 

  • Register Relative:

Stack Addressing Modes

  • The stack is used to hold temporary variables and stores return addresses for procedures.
    • push and pop instructions are used to manipulate it.
    • call and ret also refer to the stack implicitly.

 

  • Two registers maintain the stack, esp and ss .
    • A LIFO (Last-in, First-out) policy is used.
    • The stack grows toward lower address.
    • Data may be pushed from any of the registers or segment registers.
      • Data may be popped into any register except cs.

Purpose of Stack

 

  • Memory used to pass parameters to procedures.

 

  • Memory used for allocating space for local variables.

 

  • Save return address in procedure calls.

 

  • Save registers to be preserved across procedure calls.

Passing Parameters to Procedures

Call Frames

Setting up Call Frames

Reading Arguments

Reading Arguments

Get argument and Return

Purpose of Stack

 

  • Memory used to pass parameters to procedures.

 

  • Memory used for allocating space for local variables.

 

  • Save return address in procedure calls.

 

  • Save registers to be preserved across procedure calls.

Passing Parameters to Procedures

Call Frames

Setting up Call Frames

Reading Arguments

Reading Arguments

Get argument and Return

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