CSI 212 Chapter 5 Slides, Spring 2012

Assembly Language for Intel-Based Assembly Language for Intel-Based Computers, 5 Computers, 5th th Edition Edition Chapter 5: Procedures (c) Pearson Education, 2002. All rights reserved. You may modify and copy this slide show for your personal use, or for use in the classroom, as long as this copyright statement, the author's name, and the title are not changed. Slides prepared by the author Revision date: June 4, 2006 Kip R. Irvine Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 2 Chapter Overview Chapter Overview • Linking to an External Library • The Book's Link Library • Stack Operations • Defining and Using Procedures • Program Design Using Procedures Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 3 The Book's Link Library The Book's Link Library • Link Library Overview • Calling a Library Procedure • Linking to a Library • Library Procedures – Overview • Six Examples Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 4 Link Library Overview Link Library Overview • A file containing procedures that have been compiled into machine code • constructed from one or more OBJ files • To build a library, . . . • start with one or more ASM source files • assemble each into an OBJ file • create an empty library file (extension .LIB) • add the OBJ file(s) to the library file, using the Microsoft LIB utility Take a quick look at Irvine32.asm by clicking on Examples at the bottom of this screen. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 5 Calling a Library Procedure Calling a Library Procedure INCLUDE Irvine32.inc .code mov eax,1234h ; input argument call WriteHex ; show hex number call Crlf ; end of line • Call a library procedure using the CALL instruction. Some procedures require input arguments. The INCLUDE directive copies in the procedure prototypes (declarations). • The following example displays "1234" on the console: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 6 Linking to a Library Linking to a Library • Your programs link to Irvine32.lib using the linker command inside a batch file named make32.bat. • Notice the two LIB files: Irvine32.lib, and kernel32.lib • the latter is part of the Microsoft Win32 Software Development Kit (SDK) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 7 What's Next What's Next • Linking to an External Library • The Book's Link Library • Stack Operations • Defining and Using Procedures • Program Design Using Procedures Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 8 Library Procedures - Overview Library Procedures - Overview (1 of 4) (1 of 4) CloseFile – Closes an open disk file Clrscr - Clears console, locates cursor at upper left corner CreateOutputFile - Creates new disk file for writing in output mode Crlf - Writes end of line sequence to standard output Delay - Pauses program execution for n millisecond interval DumpMem - Writes block of memory to standard output in hex DumpRegs – Displays general-purpose registers and flags (hex) GetCommandtail - Copies command-line args into array of bytes GetMaxXY - Gets number of cols, rows in console window buffer GetMseconds - Returns milliseconds elapsed since midnight Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 9 Library Procedures - Overview Library Procedures - Overview (2 of 4) (2 of 4) GetTextColor - Returns active foreground and background text colors in the console window Gotoxy - Locates cursor at row and column on the console IsDigit - Sets Zero flag if AL contains ASCII code for decimal digit (0–9) MsgBox, MsgBoxAsk – Display popup message boxes OpenInputFile – Opens existing file for input ParseDecimal32 – Converts unsigned integer string to binary ParseInteger32 - Converts signed integer string to binary Random32 - Generates 32-bit pseudorandom integer in the range 0 to FFFFFFFFh Randomize - Seeds the random number generator RandomRange - Generates a pseudorandom integer within a specified range ReadChar - Reads a single character from standard input Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 10 Library Procedures - Overview Library Procedures - Overview (3 of 4) (3 of 4) ReadFromFile – Reads input disk file into buffer ReadDec - Reads 32-bit unsigned decimal integer from keyboard ReadHex - Reads 32-bit hexadecimal integer from keyboard ReadInt - Reads 32-bit signed decimal integer from keyboard ReadKey – Reads character from keyboard input buffer ReadString - Reads string from standard input, terminated by [Enter] SetTextColor - Sets foreground and background colors of all subsequent console text output StrLength – Returns length of a string WaitMsg - Displays message, waits for Enter key to be pressed WriteBin - Writes unsigned 32-bit integer in ASCII binary format. WriteBinB – Writes binary integer in byte, word, or doubleword format WriteChar - Writes a single character to standard output Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 11 Library Procedures - Overview Library Procedures - Overview (4 of 4) (4 of 4) WriteDec - Writes unsigned 32-bit integer in decimal format WriteHex - Writes an unsigned 32-bit integer in hexadecimal format WriteHexB – Writes byte, word, or doubleword in hexadecimal format WriteInt - Writes signed 32-bit integer in decimal format WriteString - Writes null-terminated string to console window WriteToFile - Writes buffer to output file WriteWindowsMsg - Displays most recent error message generated by MS-Windows Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 12 Example 1 Example 1 .code call Clrscr mov eax,500 call Delay call DumpRegs Clear the screen, delay the program for 500 milliseconds, and dump the registers and flags. EAX=00000613 EBX=00000000 ECX=000000FF EDX=00000000 ESI=00000000 EDI=00000100 EBP=0000091E ESP=000000F6 EIP=00401026 EFL=00000286 CF=0 SF=1 ZF=0 OF=0 Sample output: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 13 Example 2 Example 2 .data str1 BYTE "Assembly language is easy!",0 .code mov edx,OFFSET str1 call WriteString call Crlf Display a null-terminated string and move the cursor to the beginning of the next screen line. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 14 Example 2a Example 2a .data str1 BYTE "Assembly language is easy!",0Dh,0Ah,0 .code mov edx,OFFSET str1 call WriteString Display a null-terminated string and move the cursor to the beginning of the next screen line (use embedded CR/LF) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 15 Example 3 Example 3 IntVal = 35 .code mov eax,IntVal call WriteBin ; display binary call Crlf call WriteDec ; display decimal call Crlf call WriteHex ; display hexadecimal call Crlf Display an unsigned integer in binary, decimal, and hexadecimal, each on a separate line. 0000 0000 0000 0000 0000 0000 0010 0011 35 23 Sample output: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 16 Example 4 Example 4 .data fileName BYTE 80 DUP(0) .code mov edx,OFFSET fileName mov ecx,SIZEOF fileName – 1 call ReadString Input a string from the user. EDX points to the string and ECX specifies the maximum number of characters the user is permitted to enter. A null byte is automatically appended to the string. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 17 Example 5 Example 5 .code mov ecx,10 ; loop counter L1: mov eax,100 ; ceiling value call RandomRange ; generate random int call WriteInt ; display signed int call Crlf ; goto next display line loop L1 ; repeat loop Generate and display ten pseudorandom signed integers in the range 0 – 99. Pass each integer to WriteInt in EAX and display it on a separate line. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 18 Example 6 Example 6 .data str1 BYTE "Color output is easy!",0 .code mov eax,yellow + (blue * 16) call SetTextColor mov edx,OFFSET str1 call WriteString call Crlf Display a null-terminated string with yellow characters on a blue background. The background color is multiplied by 16 before being added to the foreground color. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 19 Multiplication and Division Instructions Multiplication and Division Instructions • MUL Instruction • IMUL Instruction • DIV Instruction • Signed Integer Division • CBW, CWD, CDQ Instructions • IDIV Instruction • Implementing Arithmetic Expressions Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 20 MUL Instruction MUL Instruction • The MUL (unsigned multiply) instruction multiplies an 8-, 16-, or 32-bit operand by either AL, AX, or EAX. • The instruction formats are: MUL r/m8 MUL r/m16 MUL r/m32 Implied operands: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 21 MUL Examples MUL Examples 100h * 2000h, using 16-bit operands: .data val1 WORD 2000h val2 WORD 100h .code mov ax,val1 mul val2 ; DX:AX = 00200000h, CF=1 The Carry flag indicates whether or not the upper half of the product contains significant digits. mov eax,12345h mov ebx,1000h mul ebx ; EDX:EAX = 0000000012345000h, CF=0 12345h * 1000h, using 32-bit operands: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 22 Your turn . . . Your turn . . . mov ax,1234h mov bx,100h mul bx What will be the hexadecimal values of DX, AX, and the Carry flag after the following instructions execute? DX = 0012h, AX = 3400h, CF = 1 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 23 Your turn . . . Your turn . . . mov eax,00128765h mov ecx,10000h mul ecx What will be the hexadecimal values of EDX, EAX, and the Carry flag after the following instructions execute? EDX = 00000012h, EAX = 87650000h, CF = 1 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 24 IMUL Instruction IMUL Instruction • IMUL (signed integer multiply ) multiplies an 8-, 16-, or 32-bit signed operand by either AL, AX, or EAX • Preserves the sign of the product by sign-extending it into the upper half of the destination register Example: multiply 48 * 4, using 8-bit operands: mov al,48 mov bl,4 imul bl ; AX = 00C0h, OF=1 OF=1 because AH is not a sign extension of AL. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 25 IMUL Examples IMUL Examples Multiply 4,823,424 * 423: mov eax,4823424 mov ebx,-423 imul ebx ; EDX:EAX = FFFFFFFF86635D80h, OF=0 OF=0 because EDX is a sign extension of EAX. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 26 Your turn . . . Your turn . . . mov ax,8760h mov bx,100h imul bx What will be the hexadecimal values of DX, AX, and the Carry flag after the following instructions execute? DX = FF87h, AX = 6000h, OF = 1 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 27 DIV Instruction DIV Instruction • The DIV (unsigned divide) instruction performs 8-bit, 16-bit, and 32-bit division on unsigned integers • A single operand is supplied (register or memory operand), which is assumed to be the divisor • Instruction formats: DIV r/m8 DIV r/m16 DIV r/m32 Default Operands: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 28 DIV Examples DIV Examples Divide 8003h by 100h, using 16-bit operands: mov dx,0 ; clear dividend, high mov ax,8003h ; dividend, low mov cx,100h ; divisor div cx ; AX = 0080h, DX = 3 Same division, using 32-bit operands: mov edx,0 ; clear dividend, high mov eax,8003h ; dividend, low mov ecx,100h ; divisor div ecx ; EAX = 00000080h, EDX = 3 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 29 Your turn . . . Your turn . . . mov dx,0087h mov ax,6000h mov bx,100h div bx What will be the hexadecimal values of DX and AX after the following instructions execute? Or, if divide overflow occurs, you can indicate that as your answer: DX = 0000h, AX = 8760h Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 30 Your turn . . . Your turn . . . mov dx,0087h mov ax,6002h mov bx,10h div bx What will be the hexadecimal values of DX and AX after the following instructions execute? Or, if divide overflow occurs, you can indicate that as your answer: Divide Overflow Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 31 Signed Integer Division Signed Integer Division • Signed integers must be sign-extended before division takes place • fill high byte/word/doubleword with a copy of the low byte/word/doubleword's sign bit • For example, the high byte contains a copy of the sign bit from the low byte: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 32 CBW, CWD, CDQ Instructions CBW, CWD, CDQ Instructions • The CBW, CWD, and CDQ instructions provide important sign-extension operations: • CBW (convert byte to word) extends AL into AH • CWD (convert word to doubleword) extends AX into DX • CDQ (convert doubleword to quadword) extends EAX into EDX • Example: mov eax,0FFFFFF9Bh ; (-101) cdq ; EDX:EAX = FFFFFFFFFFFFFF9Bh Your copy of the book may have an error on page 243: 9Bh equals –101 rather than –65. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 33 IDIV Instruction IDIV Instruction • IDIV (signed divide) performs signed integer division • Same syntax and operands as DIV instruction Example: 8-bit division of –48 by 5 mov al,-48 cbw ; extend AL into AH mov bl,5 idiv bl ; AL = -9, AH = -3 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 34 IDIV Examples IDIV Examples Example: 32-bit division of –48 by 5 mov eax,-48 cdq ; extend EAX into EDX mov ebx,5 idiv ebx ; EAX = -9, EDX = -3 Example: 16-bit division of –48 by 5 mov ax,-48 cwd ; extend AX into DX mov bx,5 idiv bx ; AX = -9, DX = -3 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 35 Your turn . . . Your turn . . . mov ax,0FDFFh ; -513 cwd mov bx,100h idiv bx What will be the hexadecimal values of DX and AX after the following instructions execute? Or, if divide overflow occurs, you can indicate that as your answer: DX = FFFFh (1), AX = FFFEh (2) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 36 Unsigned Arithmetic Expressions Unsigned Arithmetic Expressions • Some good reasons to learn how to implement integer expressions: • Learn how do compilers do it • Test your understanding of MUL, IMUL, DIV, IDIV • Check for overflow (Carry and Overflow flags) Example: var4 = (var1 + var2) * var3 ; Assume unsigned operands mov eax,var1 add eax,var2 ; EAX = var1 + var2 mul var3 ; EAX = EAX * var3 jc TooBig ; check for carry mov var4,eax ; save product Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 37 Signed Arithmetic Expressions Signed Arithmetic Expressions (1 of 2) (1 of 2) Example: eax = (-var1 * var2) + var3 mov eax,var1 neg eax imul var2 jo TooBig ; check for overflow add eax,var3 jo TooBig ; check for overflow Example: var4 = (var1 * 5) / (var2 – 3) mov eax,var1 ; left side mov ebx,5 imul ebx ; EDX:EAX = product mov ebx,var2 ; right side sub ebx,3 idiv ebx ; EAX = quotient mov var4,eax Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 38 Signed Arithmetic Expressions Signed Arithmetic Expressions (2 of 2) (2 of 2) Example: var4 = (var1 * -5) / (-var2 % var3); mov eax,var2 ; begin right side neg eax cdq ; sign-extend dividend idiv var3 ; EDX = remainder mov ebx,edx ; EBX = right side mov eax,-5 ; begin left side imul var1 ; EDX:EAX = left side idiv ebx ; final division mov var4,eax ; quotient Sometimes it's easiest to calculate the right-hand term of an expression first. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 39 Your turn . . . Your turn . . . mov eax,20 imul ebx idiv ecx Implement the following expression using signed 32-bit integers: eax = (ebx * 20) / ecx Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 40 Your turn . . . Your turn . . . mov eax,var1 mov edx,var2 neg edx imul edx ; left side: EDX:EAX mov ecx,var3 sub ecx,ebx idiv ecx ; EAX = quotient mov var3,eax Implement the following expression using signed 32-bit integers. Do not modify any variables other than var3: var3 = (var1 * -var2) / (var3 – ebx) Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 41 What's Next What's Next • Linking to an External Library • The Book's Link Library • Stack Operations • Defining and Using Procedures • Program Design Using Procedures Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 42 Stack Operations Stack Operations • Runtime Stack • PUSH Operation • POP Operation • PUSH and POP Instructions • Using PUSH and POP • Example: Reversing a String • Related Instructions Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 43 Runtime Stack Runtime Stack • Imagine a stack of plates . . . • plates are only added to the top • plates are only removed from the top • LIFO structure Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 44 Runtime Stack Runtime Stack • Managed by the CPU, using two registers • SS (stack segment) • ESP (stack pointer) * * SP in Real-address mode Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 45 PUSH Operation PUSH Operation (1 of 2) (1 of 2) • A 32-bit push operation decrements the stack pointer by 4 and copies a value into the location pointed to by the stack pointer. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 46 PUSH Operation PUSH Operation (2 of 2) (2 of 2) • Same stack after pushing two more integers: The stack grows downward. The area below ESP is always available (unless the stack has overflowed). Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 47 POP Operation POP Operation • Copies value at stack[ESP] into a register or variable. • Adds n to ESP, where n is either 2 or 4. • value of n depends on the attribute of the operand receiving the data Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 48 PUSH and POP Instructions PUSH and POP Instructions • PUSH syntax: • PUSH r/m16 • PUSH r/m32 • PUSH imm32 • POP syntax: • POP r/m16 • POP r/m32 Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 49 Using PUSH and POP Using PUSH and POP push esi ; push registers push ecx push ebx mov esi,OFFSET dwordVal ; display some memory mov ecx,LENGTHOF dwordVal mov ebx,TYPE dwordVal call DumpMem pop ebx ; restore registers pop ecx pop esi Save and restore registers when they contain important values. PUSH and POP instructions occur in the opposite order. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 50 Example: Nested Loop Example: Nested Loop mov ecx,100 ; set outer loop count L1: ; begin the outer loop push ecx ; save outer loop count mov ecx,20 ; set inner loop count L2: ; begin the inner loop ; ; loop L2 ; repeat the inner loop pop ecx ; restore outer loop count loop L1 ; repeat the outer loop When creating a nested loop, push the outer loop counter before entering the inner loop: Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 51 Example: Reversing a String Example: Reversing a String • Use a loop with indexed addressing • Push each character on the stack • Start at the beginning of the string, pop the stack in reverse order, insert each character back into the string • Source code • Q: Why must each character be put in EAX before it is pushed? Because only word (16-bit) or doubleword (32-bit) values can be pushed on the stack. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 52 Your turn . . . Your turn . . . • Using the String Reverse program as a starting point, • #1: Modify the program so the user can input a string containing between 1 and 50 characters. • #2: Modify the program so it inputs a list of 32-bit integers from the user, and then displays the integers in reverse order. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 53 Related Instructions Related Instructions • PUSHFD and POPFD • push and pop the EFLAGS register • PUSHAD pushes the 32-bit general-purpose registers on the stack • order: EAX, ECX, EDX, EBX, ESP, EBP, ESI, EDI • POPAD pops the same registers off the stack in reverse order • PUSHA and POPA do the same for 16-bit registers Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 54 Your Turn . . . Your Turn . . . • Write a program that does the following: • Assigns integer values to EAX, EBX, ECX, EDX, ESI, and EDI • Uses PUSHAD to push the general-purpose registers on the stack • Using a loop, your program should pop each integer from the stack and display it on the screen Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 55 What's Next What's Next • Linking to an External Library • The Book's Link Library • Stack Operations • Defining and Using Procedures • Program Design Using Procedures Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 56 Defining and Using Procedures Defining and Using Procedures • Creating Procedures • Documenting Procedures • Example: SumOf Procedure • CALL and RET Instructions • Nested Procedure Calls • Local and Global Labels • Procedure Parameters • Flowchart Symbols • USES Operator Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 57 Creating Procedures Creating Procedures • Large problems can be divided into smaller tasks to make them more manageable • A procedure is the ASM equivalent of a Java or C++ function • Following is an assembly language procedure named sample: sample PROC . . ret sample ENDP Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 58 Documenting Procedures Documenting Procedures • A description of all tasks accomplished by the procedure. • Receives: A list of input parameters; state their usage and requirements. • Returns: A description of values returned by the procedure. • Requires: Optional list of requirements called preconditions that must be satisfied before the procedure is called. Suggested documentation for each procedure: If a procedure is called without its preconditions satisfied, it will probably not produce the expected output. Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 59 Example: SumOf Procedure Example: SumOf Procedure ;--------------------------------------------------------- SumOf PROC ; ; Calculates and returns the sum of three 32-bit integers. ; Receives: EAX, EBX, ECX, the three integers. May be ; signed or unsigned. ; Returns: EAX = sum, and the status flags (Carry, ; Overflow, etc.) are changed. ; Requires: nothing ;--------------------------------------------------------- add eax,ebx add eax,ecx ret SumOf ENDP Web site Examples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 60 CALL and RET Instructions CALL and RET Instructions • The CALL instruction calls a procedure • pushes offset of next instruction on the stack • copies the address of the called procedure into EIP • The RET instruction returns from a procedure • pops top of stack into EIP