![Procedure Parameters (2 of 3)
33
ArraySum PROC
mov esi,0 ; array index
mov eax,0 ; set the sum to zero
mov ecx,LENGTHOF myarray ; set number of elements
L1: add eax,myArray[esi] ; add each integer to sum
add esi,4 ; point to next integer
loop L1 ; repeat for array size
mov theSum,eax ; store the sum
ret
ArraySum ENDP
The ArraySum procedure calculates the sum of an array. It makes
two references to specific variable names: myArray, theSum
What if you wanted to calculate the sum of two or three arrays
within the same program?](https://image.slidesharecdn.com/chapt56-250524021943-92a34039/85/chapt_5-6AssemblyLanguagecompleteclear-ppt-33-320.jpg)
![Procedure Parameters (3 of 3)
34
ArraySum PROC
; Receives: ESI points to an array of doublewords,
; ECX = number of array elements.
; Returns: EAX = sum
;-----------------------------------------------------
mov eax,0 ; set the sum to zero
L1: add eax,[esi] ; add each integer to sum
add esi,4 ; point to next integer
loop L1 ; repeat for array size
ret
ArraySum ENDP
This version of ArraySum returns the sum of any doubleword
array whose address is in ESI. The sum is returned in EAX:](https://image.slidesharecdn.com/chapt56-250524021943-92a34039/85/chapt_5-6AssemblyLanguagecompleteclear-ppt-34-320.jpg)
chapt_5+6AssemblyLanguagecompleteclear.ppt
- 1. ASSEMBLY LANGUAGE FOR INTEL- BASED COMPUTERS, 4TH EDITION Chapter 5 and 6 Kip R. Irvine
- 2. Chapter Overview 2 Linking to an External Library The Book's Link Library Stack Operations Defining and Using Procedures Program Design Using Procedures
- 3. The Book's Link Library 3 Link Library Overview Calling a Library Procedure Linking to a Library Library Procedures – Overview Six Examples
- 4. Link Library Overview 4 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
- 5. Calling a Library Procedure 5 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:
- 6. Linking to a Library 6 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)
- 7. Library Procedures - Overview (1 of 3) 7 Clrscr - Clears the console and locates the cursor at the upper left corner. Crlf - Writes an end of line sequence to standard output. Delay - Pauses the program execution for a specified n millisecond interval. DumpMem - Writes a block of memory to standard output in hexadecimal. DumpRegs - Displays the EAX, EBX, ECX, EDX, ESI, EDI, EBP, ESP, EFLAGS, and EIP registers in hexadecimal. Also displays the Carry, Sign, Zero, and Overflow flags. GetCommandtail - Copies the program’s command-line arguments (called the command tail) into an array of bytes. GetMseconds - Returns the number of milliseconds that have elapsed since midnight.
- 8. Library Procedures - Overview (2 of 3) 8 Gotoxy - Locates cursor at row and column on the console. Random32 - Generates a 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. ReadHex - Reads a 32-bit hexadecimal integer from standard input, terminated by the Enter key. ReadInt - Reads a 32-bit signed decimal integer from standard input, terminated by the Enter key. ReadString - Reads a string from standard input, terminated by the Enter key.
- 9. Library Procedures - Overview (3 of 3) 9 SetTextColor - Sets the foreground and background colors of all subsequent text output to the console. WaitMsg - Displays message, waits for Enter key to be pressed. WriteBin - Writes an unsigned 32-bit integer to standard output in ASCII binary format. WriteChar - Writes a single character to standard output. WriteDec - Writes an unsigned 32-bit integer to standard output in decimal format. WriteHex - Writes an unsigned 32-bit integer to standard output in hexadecimal format. WriteInt - Writes a signed 32-bit integer to standard output in decimal format. WriteString - Writes a null-terminated string to standard output.
- 10. Example 1 10 .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:
- 11. Example 2 11 .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.
- 12. Example 2a 12 .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)
- 13. Example 3 13 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:
- 14. Example 4 14 .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.
- 15. Example 5 15 .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.
- 16. Example 6 16 .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.
- 17. Using PUSH and POP 17 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.
- 18. Example: Nested Loop 18 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 Remember the nested loop we created on page 129? It's easy to push the outer loop counter before entering the inner loop:
- 19. Example: Reversing a String 19 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.
- 20. Your turn . . . 20 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.
- 21. Related Instructions 21 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
- 22. Your Turn . . . 22 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
- 23. Defining and Using Procedures 23 Creating Procedures Documenting Procedures Example: SumOf Procedure CALL and RET Instructions Nested Procedure Calls Local and Global Labels Procedure Parameters Flowchart Symbols USES Operator
- 24. Creating Procedures 24 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
- 25. Documenting Procedures 25 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 having been satisfied, the procedure's creator makes no promise that it will work.
- 26. Example: SumOf Procedure 26 ;--------------------------------------------------------- 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
- 27. CALL and RET Instructions 27 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
- 28. CALL-RET Example (1 of 2) 28 main PROC 00000020 call MySub 00000025 mov eax,ebx . . main ENDP MySub PROC 00000040 mov eax,edx . . ret MySub ENDP 0000025 is the offset of the instruction immediately following the CALL instruction 00000040 is the offset of the first instruction inside MySub
- 29. CALL-RET Example (2 of 2) 29 The CALL instruction pushes 00000025 onto the stack, and loads 00000040 into EIP The RET instruction pops 00000025 from the stack into EIP (stack shown before RET executes)
- 30. Nested Procedure Calls 30 By the time Sub3 is called, the stack contains all three return addresses:
- 31. Local and Global Labels 31 main PROC jmp L2 ; error L1:: ; global label exit main ENDP sub2 PROC L2: ; local label jmp L1 ; ok ret sub2 ENDP A local label is visible only to statements inside the same procedure. A global label is visible everywhere.
- 32. Procedure Parameters (1 of 3) 32 A good procedure might be usable in many different programs but not if it refers to specific variable names Parameters help to make procedures flexible because parameter values can change at runtime
- 33. Procedure Parameters (2 of 3) 33 ArraySum PROC mov esi,0 ; array index mov eax,0 ; set the sum to zero mov ecx,LENGTHOF myarray ; set number of elements L1: add eax,myArray[esi] ; add each integer to sum add esi,4 ; point to next integer loop L1 ; repeat for array size mov theSum,eax ; store the sum ret ArraySum ENDP The ArraySum procedure calculates the sum of an array. It makes two references to specific variable names: myArray, theSum What if you wanted to calculate the sum of two or three arrays within the same program?
- 34. Procedure Parameters (3 of 3) 34 ArraySum PROC ; Receives: ESI points to an array of doublewords, ; ECX = number of array elements. ; Returns: EAX = sum ;----------------------------------------------------- mov eax,0 ; set the sum to zero L1: add eax,[esi] ; add each integer to sum add esi,4 ; point to next integer loop L1 ; repeat for array size ret ArraySum ENDP This version of ArraySum returns the sum of any doubleword array whose address is in ESI. The sum is returned in EAX: