ct215: assembly language programming
DESCRIPTION
Ct215: Assembly Language Programming. Chapter 5: Procedures. Procedures. Procedure Definition i.e., the code of the procedure routine Associated with a label Procedure Call Ideally, p (a 1 ,…,a n ) Very similar to a jump: JMP Label p - PowerPoint PPT PresentationTRANSCRIPT
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Ct215: Assembly Language Programming Ct215: Assembly Language Programming
Chapter 5: Procedures
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ProceduresProcedures• Procedure Definition
• i.e., the code of the procedure routine• Associated with a label
• Procedure Call • Ideally, p (a1,…,an)• Very similar to a jump: JMP Labelp
• …except that means of passing the parameters to p must be decided•One idea: pass parameters in registers•Another idea: pass them on the “stack”
• If you want to know how your favorite programming language handle procedures, this is where you find out
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Chapter OverviewChapter Overview
• Using predefined procedures• Linking to an External Library• The Book's Link Library
• Stack Operations• Defining and Using your own Procedures• Program Design Using Procedures
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The Book's Link LibraryThe Book's Link Library
• Link Library Overview• Calling a Library Procedure• Linking to a Library• Library Procedures – Overview• Six Examples
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Link Library OverviewLink Library Overview
• A file containing procedures that have been compiled into machine code• constructed from one or more OBJ files
• To build a library under Windows, . . .• 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 – it contains a large number of useful procedures.
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Calling a Library ProcedureCalling a Library Procedure
INCLUDE Irvine32.inc.code
mov eax,1234h ; input argumentcall WriteHex ; show hex numbercall Crlf ; end of line
การเรยก procedure จาก Library โดยการใชคำาสง CALL บาง procedures ตองการกำาหนดคาอนพตของ arguments ซงการทำางานคำาสงเทยม INCLUDE directive จะทำาสำาเนารปแบบของ procedure เพอแสดงใหเหน Procedures
ตวอยางการแสดงผลในการพมพคา "1234" ทจอภาพ :
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ตวอยางการแสดงผลในการพมพคา "1234" ทจอภาพ :
INCLUDE Irvine32.inc ; เปนการประกาศในการใช Library
.code ; เปนคำาสงเทยมทบอกคาของ Code segment
mov eax,1234h ; input argumentcall WriteHex ; show hex numbercall Crlf ; end of line
•การทำางานในโปรแกรมจะมการเชอมเขากบ Irvine32.lib โดยใชคำาสงในการจาก linker ทอยภายใต batch file ขอ make32.bat.•Notice the two LIB files: Irvine32.lib, and kernel32.lib
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Linking to a LibraryLinking 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)
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Library Procedures
Clrscr – โปรแกรมยอยนเปนการเคลยจอภาพทงจอภาพ บรรทด 0 คอลมน 0 จนถง บรรทด 24 คอลมน 79 .
Crlf – โปรแกรมยอยนเปนการทำางานถงการสนสดบรรทดและขนบรรทดใหม
Delay - โปรแกรมยอยนเปนการหนวงเวลาในการเอกซควสคำาสงทกำาหนดเปน n millisecond interval.
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DumpMem - โปรแกรมยอยนเปนการพมพขอมลทอยในหนวยความจำาเปนกลมและแสดงผลในรปเลขฐานสบหก
DumpRegs – โปรแกรมยอยนเปนการแสดงผลลพธขอมลของรจสเตอร EAX, EBX, ECX, EDX, ESI, EDI, EBP, ESP, EFLAGS, and EIP registers เปนเลขฐานสบหกและแสดงคาของแฟลกทเกดขนดงน Carry, Sign, Zero, and Overflow flags.
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GetCommandtail - โปรแกรมยอยนเปนการทำาสำาเนาคำาสงในโปรแกรมในรปของอะเรย
GetMseconds - Returns the number of milliseconds that have elapsed since midnight.
Gotoxy – โปรแกรมยอยนเปนกำาหนดตำาแหนงของเคอรเซอรบนจอภาพ.
Random32 – โปรแกรมยอยนเปนการจายคาของการสมขอมลเลขจำานวนเตมขนาด 32 บตระหวาง 0 to FFFFFFFFh.
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Randomize - Seeds the random number generator.
RandomRange – โปรแกรมยอยนเปนการสมตามทกำาหนด .
ReadChar - โปรแกรมยอยนเปนการอานคาตวอกขระจากหนวยรบขอมลคอคยบอรด.
ReadHex – โปรแกรมยอยนเปนการอานจำานวนเตมเลขฐานสบหกขนาด 32 บตจากคยบอรดและสนสดการรบดวยคย Enter key.
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ReadInt – โปรแกรมยอยนเปนการอานคาเลขจำานวนเตมฐานสบแบบคดเครองหมายจากคยบอรดและสนสกดวยคย Enter key.
ReadString – โปรแกรมยอยนเปนการอานคาสตรงจากคยบอรดและสนสดดวยคย Enter key.
SetTextColor – โปรแกรมยอยนเปนการกำาหนเคาสของ foreground และ background ในการกำาหนดคาสของ text บนจอภาพ.
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WaitMsg – โปรแกรมยอยนเปนการแสดงขอความทปรากฏจนกวาจะกดคย Enter key
WriteBin – โปรแกรมยอยนเปนการพมพคาเลขจำานวนเตมขนาด 32 บตไมคดเครองหมายบนจอภาพในรปของ ASCII binary format.
WriteChar – โปรแกรมยอยนเปนการพพมตวอกขระทละตวบนจอภาพ .
WriteDec – โปรแกรมยอยนเปนการพมพคาเลขจำานวนตมขนาด 32 บตไมคดเครองหมายบนจอภาพในรปของ decimal format.
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WriteHex - โปรแกรมยอยนเปนการพมพคาเลขจำานวนตมขนาด 32 บตไมคดเครองหมายบนจอภาพในรปของ hexadecimal format.
WriteInt - โปรแกรมยอยนเปนการพมพคาเลขจำานวนตมขนาด 32 บตคดเครองหมายบนจอภาพในรปของ decimal format.
WriteString – โปรแกรมยอยนเปนการพมพคาสตรงบนจอภาพ.
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.codecall Clrscrmov eax,500call Delaycall DumpRegs
Example 1การเคลยจอภาพ (Clear the screen) และใหโปรแกรมหนวงเวลา 500 milliseconds และแสดงผลลพธในรจสเตอรลคาของแฟลก .
EAX=00000613 EBX=00000000 ECX=000000FF EDX=00000000ESI=00000000 EDI=00000100 EBP=0000091E ESP=000000F6EIP=00401026 EFL=00000286 CF=0 SF=1 ZF=0 OF=0
Sample output:
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.datastr1 BYTE "Assembly language is easy!",0
.codemov edx,OFFSET str1call WriteStringcall Crlf
Example 2การแสดงผลลพธของคาสตรง และเลอนเคอรเซอรไปยงจดเรมตนของบรรทดแรกของจอภาพถดไป.
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Example 2aExample 2a
.datastr1 BYTE "Assembly language is easy!",0Dh,0Ah,0
.codemov edx,OFFSET str1call WriteString
การแสดงผลลพธของคาสตรง และเลอนเคอรเซอรไปยงจดเรมตนของบรรทดใหมของจอภาพ (use embedded
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Example 3Example 3
IntVal = 35.code
mov eax,IntValcall WriteBin ; display binarycall Crlfcall WriteDec ; display decimalcall Crlfcall WriteHex ; display hexadecimalcall Crlf
การแสดงผลลพธคาจำานวนเตมเลขฐานสองไมคดครองหมายเลชฐานสบและเลขฐานสบหกโดยแยกแตละบรรทด.
0000 0000 0000 0000 0000 0000 0010 00113523
Sample output:
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Example 4Example 4
.datafileName BYTE 80 DUP(0)
.codemov edx,OFFSET fileNamemov ecx,SIZEOF fileName – 1call ReadString
การพมพคาสตรงทปอนเขามาของผใช รจสเตอร EDX จะเปนตวชคาของสตรง และรจสเตอร ECX กำาหนดคาของตวอกขระสงสดทผใชจะปอนเขามา.
A null byte is automatically appended to the string.
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Example 5Example 5
.codemov ecx,10 ; loop counter
L1:mov eax,100 ; ceiling valuecall RandomRange; generate random intcall WriteInt ; display signed intcall Crlf ; goto next display lineloop L1 ; repeat loop
เปนการแสดงผลแบบสมเลขชำานวนเตมทคดเครองหมายในชวง 0 – 99. เลขจำานวนเตมแตละคาใชการพมพดวยโปรแกรมยอยทเรยกวา WriteInt และขอมลทพมพเกบใน EAX และแสดผลทละบรรทด ..
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Example 6Example 6
.datastr1 BYTE "Color output is easy!",0
.codemov eax,yellow + (blue * 16)call SetTextColormov edx,OFFSET str1call WriteStringcall Crlf
เปนการแสดงคาของแอตทรบวสของตวสตรงทมพนทสนำาเงนและตวอกขระสเหลอง
The background color is multiplied by 16 before being added to the foreground color.
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Procedure Descriptions
CLRSCR
เปนการทำางานในการเคลยจอภาพ Call Clrscr
Crlf
เปนการทำางานของการสนสดบรรทดและขนบรรทดใหม (0Dh,0Ah) หรอเปนการเลอนเคอรเซอรไปยงบรรทดใหมของจอภาพ. call Crlf
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Delay
เปนการทำางานในการหนวงเวลาของโปรแกรมทกำาหนดคามาพรอมกบคำาสง เมอการเรยกโปรแกรมยอยนDelay procedure pauses the program for a specified time interval. When calling function, set EAX to desired interval, in milliseconds
Mov eax, 1000 ; 1 secondCall delay
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DumpRegs
เปนการแสดงคาของรจสเตอรในปจจบนบนจอภาพ ซงการใชงานหลกจะเปนการใชงานของโปรแกรมดบก debugging. โปรแกรมยอย DumpRegs จะพมพผลลพธขอมลในรจสเตอร รวมถงคาในแฟลก แตการทำางานจะไมเปลยนแปลงคาในรจสเตอร
Example:call DumpRegsExample Output (CF=Carry Flag, SF=Sign Flag, ZF=Zero Flag and OF=Overflow Flag):EAX=00000005 EBX=7FFDF000 ECX=00000101 EDX=FFFFFFFFESI=00000000 EDI=00130178 EBP=0012FFF0 ESP=0012FFC4EIP=0040100A EFL=00000246 CF=0 SF=0 ZF=1 OF=0
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Dumpmemโปรแกรมยอยนจะพมพผลลพธในรปเลขฐานสบหก
เปนกลมในชวงระหวางทกำาหนดโดยรจสเตอร ESI , และจำานวนคาทแสดงเกบในรจสเตอร ECX และขนาดของการพมพเกบใน EBX ( 1 = byte , 2 = word , 4 doubleword)
.dataarray dword 1,2,3,4,5,6,7,8,9,0aH,0dH
main procmov esi,offset arraymov ecx,lengthof arraymov ebx,type arraycall dumpmem
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Exit
การทำางานสวนนเปนแมคโคร ซงเปนสวนของการสนสดโปรแกรมและใหกบไปท operating system.
Example: main proc
……. exit
main endpend
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Gotoxy
เปนการกำาหนดตำาแหนงบรรทดและคอลมนของเคอเซอรบนจอภาพ คาของตำาแหนงจะสงผานไปยงรจสเตอร DH และ DL สามารถกำาหนดในชวง 0 to X-1 และจาก 0 to Y-1, ขณะท X คอคาของคอลมน และ Y คอคาของบรรทดบนจอภาพ เราจะกำาหนดคาบนจอภาพได 25 บรรทด และ 80 คอลมน .
Input Parameters:DH = rowDL = column
Example:
mov dl,79 ;column mov dh,24 ;row call Gotoxy
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ReadChar
เปนการอานคาตวอกขระทละตวจากคยบอรดและตวอกขระจะถกนำามาเกบไวในรจสเตอร AL แตตวอกขระจะไมปรากฏทจอภาพ
Output: AL = ACSII code
Example:data
charIn BYTE ?.codecall ReadCharmov charIn,alcmp charIn, 'A'je doMoveLeft
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RandomRangeGenerates an unsigned pseudo-random 32-bit integer in the range of 0 through (n-1).
Input Parameters:EAX = n, the range
Output: EAX = random (0 to n-1)
Example:;Get a random number from 1 to 100
.dataranNum DWORD ?
.codemov eax,100 ;get random 0 to 99call RandomRange ;inc eax ;make range 1 to 100mov ranNum,eax ;save random
number
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ReadIntReads a 32-bit signed decimal integer from standard input, stopping when the Enter key is pressed. All valid digits occurring before a non-numeric character are converted to the integer value. Leading spaces are ignored, and an optional leading + or - sign is permitted. ReadInt will display an error message, set the Overflow flag, and reset EAX to zero if the value entered cannot be represented as a 32-bit signed integer.Input Parameters: NoneOutput: if OF=0, EAX = valid binary value, and SF=sign. If OF=1, EAX = 0 (invalid input)Example:
.dataintNum DWORD ?.codecall ReadIntmov intNum, eax
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ReadHexReadhex procedure reads a 32 bit hexadecimal integer form standard input and reurns the value in EAX
.datahexval dword ?
.codecall readhexmov hexval,eax
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ReadstringReadstring procedure reads a string form standard input. Stooping when the user process the Enter key.
The following statements call Readstring ,passing ECX and EDX
.databuffer byte 50 dup(0)bytecount dword ?
.codemov edx,offset buffer ; point to
buffermov ecx,(Sizeof buffer); specify max
characteracall readstring ;input the stringmov bytecount,eax ;number of characters
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Example
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.
.datafileName BYTE 80 DUP(0)
.codemov edx,OFFSET fileNamemov ecx,SIZEOF fileName – 1call ReadString
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WriteChar
Writes a single character to standard output.Input Parameters:AL = the character to write
Example:mov al,'A'call WriteChar
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WriteDec
Writes an unsigned 32-bit decimal number to standard output in decimal format with no leading zeros.
Input Parameters:EAX = unsigned number to writeOutput: noneExample: mov eax,123456 call WriteDec
Output: 123456
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WriteInt
Writes a signed 32-bit decimal number to standard output in decimal format with a leading sign and no leading zeros.
Input Parameters: EAX = signed number to writeOutput: NoneExample: mov eax,216543 call WriteInt
Output as on console: +216543
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Writehex
The write procedure writes a32 bit unsigned interger to standard output in 8 digit hexadecimal format.
Mov eax,7FFFHCall writehex ;display :00007FFF
Writebin
Wirtebin procedure writes an to stabdard output in ASCII binary format
Move ax,12345678HCall writebin
;display 0001 0010 0011 0100 0101 0110 0111 1000
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ExampleDisplay an unsigned integer in binary, decimal, and hexadecimal, each on a separate lineIntVal = 35
.codemov eax,IntValcall WriteBin ; display binarycall Crlfcall WriteDec ; display decimalcall Crlfcall WriteHex ; display hexadecimalcall Crlf
Sample output:0000 0000 0000 0000 0000 0000 0010 00113523
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Example
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
.codemov ecx,10 ; loop counter
L1: mov eax,100 ; ceiling valuecall RandomRange ; generate random
intcall WriteInt ; display signed intcall Crlf ; goto next display lineloop L1 ; repeat loop
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Stack OperationsStack Operations
• Runtime Stack• PUSH Operation• POP Operation• PUSH and POP Instructions• Using PUSH and POP• Example: Reversing a String• Related Instructions
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Runtime StackRuntime Stack• Imagine a stack of plates . . .
• plates are only added to the top• plates are only removed from the top• LIFO structure
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Runtime StackRuntime Stack• Managed by the CPU, using two registers
• SS (stack segment)• ESP (stack pointer) *
* SP in Real-address mode
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PUSH OperationPUSH 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.
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PUSH OperationPUSH 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).
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POP OperationPOP 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
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PUSH and POP InstructionsPUSH and POP Instructions
• PUSH syntax:• PUSH r/m16• PUSH r/m32• PUSH imm32
• POP syntax:• POP r/m16• POP r/m32
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Using PUSH and POPUsing PUSH and POP
push esi ; push registerspush ecxpush ebx
mov esi,OFFSET dwordVal ; display some memorymov ecx,LENGTHOF dwordValmov ebx,TYPE dwordValcall DumpMem
pop ebx ; restore registerspop ecxpop esi
Save and restore registers when they contain important values. PUSH and POP instructions occur in the opposite order.
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Example: Nested LoopExample: Nested Loop
mov ecx,100 ; set outer loop countL1: ; begin the outer loop
push ecx ; save outer loop count
mov ecx,20 ; set inner loop countL2: ; begin the inner loop
;;loop L2 ; repeat the inner loop
pop ecx ; restore outer loop countloop 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:
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Example: Reversing a StringExample: 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.
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Related InstructionsRelated 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
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Defining and Using ProceduresDefining 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
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Creating ProceduresCreating 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
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Documenting ProceduresDocumenting 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 having been satisfied, the procedure's creator makes no promise that it will work.
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Example: SumOf ProcedureExample: 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,ebxadd eax,ecxret
SumOf ENDP
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CALL and RET InstructionsCALL 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
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CALL-RET ExampleCALL-RET Example (1 of 2) (1 of 2)
main PROC00000020 call MySub00000025 mov eax,ebx..
main ENDP
MySub PROC00000040 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
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CALL-RET ExampleCALL-RET Example (2 of 2) (2 of 2)
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)
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Nested Procedure CallsNested Procedure Calls
By the time Sub3 is called, the stack contains all three return addresses:
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Local and Global LabelsLocal and Global Labels
main PROCjmp L2 ; error
L1:: ; global labelexit
main ENDP
sub2 PROCL2: ; local label
jmp L1 ; okret
sub2 ENDP
A local label is visible only to statements inside the same procedure. A global label is visible everywhere.
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Procedure ParametersProcedure Parameters (1 of 3) (1 of 3)
• 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
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Procedure ParametersProcedure Parameters (2 of 3) (2 of 3)
ArraySum PROCmov esi,0 ; array indexmov eax,0 ; set the sum to zeromov ecx,LENGTHOF myarray ; set number of elements
L1:add eax,myArray[esi] ; add each integer to sumadd esi,4 ; point to next integerloop L1 ; repeat for array size
mov theSum,eax ; store the sumret
ArraySum ENDP
The ArraySum procedure calculates the sum of an array. It makes two references to specific variable names:
What if you wanted to calculate the sum of two or three arrays within the same program?
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Procedure ParametersProcedure Parameters (3 of 3) (3 of 3)
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 zeroL1: add eax,[esi] ; add each integer to sum
add esi,4 ; point to next integerloop L1 ; repeat for array sizeret
ArraySum ENDP
This version of ArraySum returns the sum of any doubleword array whose address is in ESI. The sum is returned in EAX:
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Flowchart SymbolsFlowchart Symbols
• The following symbols are the basic building blocks of flowcharts:
(Includes two symbols not listed on page 166 of the book.)
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Flowchart for Flowchart for the ArraySum the ArraySum ProcedureProcedure
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USES OperatorUSES Operator• Lists the registers that will be preserved
ArraySum PROC USES esi ecxmov eax,0 ; set the sum to zeroetc.
MASM generates the code shown in gold:
ArraySum PROCpush esipush ecx..pop ecxpop esiret
ArraySum ENDP
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When not to push a registerWhen not to push a register
SumOf PROC ; sum of three integerspush eax ; 1add eax,ebx ; 2add eax,ecx ; 3pop eax ; 4ret
SumOf ENDP
The sum of the three registers is stored in EAX on line (3), but the POP instruction replaces it with the starting value of EAX on line (4):
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Program Design Using ProceduresProgram Design Using Procedures
• Top-Down Design (functional decomposition) involves the following:• design your program before starting to code• break large tasks into smaller ones• use a hierarchical structure based on procedure calls• test individual procedures separately
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Integer Summation ProgramInteger Summation Program (1 of 4) (1 of 4)
Main steps:
• Prompt user for multiple integers
• Calculate the sum of the array
• Display the sum
Description: Write a program that prompts the user for multiple 32-bit integers, stores them in an array, calculates the sum of the array, and displays the sum on the screen.
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Procedure DesignProcedure Design (2 of 4) (2 of 4)
MainClrscr ; clear screenPromptForIntegers
WriteString ; display stringReadInt ; input integer
ArraySum ; sum the integersDisplaySum
WriteString ; display stringWriteInt ; display integer
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Structure ChartStructure Chart (3 of 4) (3 of 4)
gray indicates library
procedure
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Sample OutputSample Output (4 of 4) (4 of 4)
Enter a signed integer: 550
Enter a signed integer: -23
Enter a signed integer: -96
The sum of the integers is: +431