Chapter III Machine-level representation of the program

Machine-level representation of the program

3.1 Historical View

8086-〉80286-〉i386-〉i486-〉pentium-〉pentiumpro-〉pentium-〉pentium-〉pentium4-〉pentium4e-〉core 2 Duo-〉core i7

3.2 Program code

1.gcc-01–o p p1.c p2.c using first level optimization

2. The program counter (%EIP) indicates the address of the next instruction that will be executed in memory.

3. Register File

Assembly code generated by the 4.-S:C language compiler

Example: Gcc-01–s code.c will produce a compilation file code.c

3.3 Data formats

Char	Bytes	B	1
Short	Word	W	2
Int	Double word	1	4
Long int	Double word	1	4
Long Long int	—	—	4
char*	Double word	1	4
Float	Single precision	S	4
Double	Double precision	L	8
Long double	Extended Precision	T	10/12

3.4 Access Information

1. Operand indicator Type: Immediate count, register, register

2. Data transfer Instructions

instruction	Effect	Description
mov      s,d /td>	s<-d	Transfer
Movb MOVW Movl	Transfer bytes Routing Word Transfer double character
movs     s,d	d<-symbol extension (S)	Transfer byte of symbol extension
movz     s,d /td>	d<-0 extension (S)	Shipping 0 Extended bytes

3.5 Arithmetic and logic operations (20135315 Han Yuqi's blog)

1. Load valid address: Leal is actually a MOVL variant that generates pointers for memory references

2. Unary operation and second courtyard operation: 1) ++,--;2) + =

• Unary operation
• -INC plus 1
• -DEC minus 1
• -NEG Take negative

-Not take compensation

• Only one operand, both a source and a destination, can be a register, or a memory location.
• Binary operation
• -Add Plus
• -SUB minus
• -Imul Multiply
• -XOR different or
• -OR OR

-AND and

• The first operand can be an immediate number, a register, or a memory location
• The second operand is both a source and a destination. Can be a register or a memory location, but not a memory location at the same time.
• Note The order of operations:

The first operand of the second operand operator

3. Shift Operation:>>,<<

• The shift amount is given first, and the second item gives the value to be shifted.
• -SAL left Shift
• -SHL left shift (equivalent to Sal)
• -SAR Arithmetic right shift

-SHR Logical Right Shift

• SOURCE operand (shift amount): Immediate number or in single-byte register element%CL.
• Intent operand: A register or a memory location.

4. Special Arithmetic operations

• Multiplication
• Product truncation
• Imull double operand

-Produces a 32-bit product from two 32-bit operands.

• Product Not truncated
• Mull unsigned number multiplication
• Imull signed number multiplication
• -Requires that one parameter must be in the register%eax and the other as the source operand of the instruction.

-The high 32 bits of the product are in%edx, and the low 32 bits are in%eax.

• Division
• Signed Division
• IDIVL operands
• -Dx:ax 64-digit number as dividend, divisor in operand

-Result: Quotient in ax, remainder in DX.

• Unsigned division
• DIVL directive

-The register%edx is usually set to 0 in advance.

3.6 Control

1. Condition Code:

CF: Carry sign ZF: 0 sign SF: symbol mark of: Overflow flag

2. Access Condition code

• Set instruction: Performs a comparison instruction and sets the condition code based on the results of the computed t=a-b

3. Jump instruction and its code: JMP *%eax

• Unconditional Jump
• Direct jump: The jump target is encoded as part of the instruction.
• Indirect jump: A jump target is read from a register or memory location.

4. Conditional delivery Instructions (reference 20135202 Shang blog)

• The most common way to translate conditional expressions and statements from C to machine languages is to combine conditional and unconditional jumps.
• Assembly structure of the If-else
• Generic form template
• if (test-expr)
• Then-statement
• Else
• Else-statement

(Note: test-expr integer expression [false/true])

• Assembly Implementation Form
• t = test-expr;
• if (!t)
• Goto false;
• Then-statement
• Goto done;
• False
• Else-statement

Done

5.switch statements

3.7 Process

1. Stack frame structure: The machine uses stack frames to pass process parameters, store return information, save registers for future replies, and local storage. The portion of the stack allocated for a single process is called a stack frame

2. Frame pointer:%EBP, stack pointer:%%esp

3. Transfer Control

Call Label Procedure Calls

Call *operand Procedure Calls

Leave to prepare the stack for return

RET returns from the procedure call

4. Register Usage Conventions

1).%eax,%edx,%ecx caller Save

2).%EBX,%esi,%edi are saved by the caller

5. Recursive procedure: Recursive invocation of a function itself is the same as calling other functions. More complex calls to each other

Problem:

1. What is the difference between the comparison instruction CMP and the subtraction instruction sub?

The Sub d,s is D-S, and the result is sent back to the destination operand.

CMP D,s is also D-S, but the results are not sent back to the target operand, and are compared using subtraction for two numeric values.

Homework

• MAIN.C:

• Assembly Code:

• To view compiler directives with VI:

• Remove the GCC generation code with "." After the start of the compiler directive:

• Analysis:

• The main function saves the%EBP and sets a new frame pointer.

  pushl%ebpmovl%esp，%ebp

• Allocating 4 bytes of stack space

  subl$4,%esp

• Set Arg1=8

  movl$8,(%esp)

• Call Invoke FH
• FH is called, initializes the frame pointer, allocates the stack space.

• %ESP (8) to%eax, which is stored in the stack

  movl%eax，（%esp）

• Call calls GH
• GH is called, initializes the stack pointer, allocates stack space

• Add%eax to immediate number 3

  add$3,%eax

• Play stack before GH ends

  popl%ebp

• RET returns the call position in FH
• FH also ends, return returns to the location of call in main

• Main continues the%eax plus 1 operation

  addl$1，%eax

• Leave to return to prepare the stack, equivalent to%ebp out of the stack, finally ret end.

Chapter III Machine-level representation of the program