Chapter 5: Procedures
Stack Operations
Copyright By PowCoder代写 加微信 powcoder
Defining and Using Procedures
Linking to an External Library
The Irvine32 Library
Program Design Using Procedures
64-Bit Assembly Programming
Runtime Stack
PUSH Operation
POP Operation
PUSH and POP Instructions
Using PUSH and POP
Example: Reversing a String
Related Instructions
Imagine a stack of plates . . .
plates are only added to the top
plates are only removed from the top
LIFO structure
192.unknown
Managed by the CPU, using two registers
SS (stack segment)
ESP (stack pointer) *
* SP in Real-address mode
193.unknown
A 32-bit push operation decrements the stack pointer by 4 and copies a value into the location pointed to by the stack pointer.
194.unknown
Same stack after pushing two more integers:
The stack grows downward. The area below ESP is always available (unless the stack has overflowed).
195.unknown
Copies value at stack[ESP] into a register or variable.
196.unknown
PUSH syntax:
PUSH r/m16
PUSH r/m32
PUSH imm32
POP syntax:
Irvine32 library always pushes 32-bit value
push esi ; push registers
mov esi,OFFSET dwordVal ; display some memory
mov ecx,LENGTHOF dwordVal
mov ebx,TYPE dwordVal
call DumpMem
pop ebx ; restore registers
Save and restore registers when they contain important values. PUSH and POP instructions occur in the opposite order.
Example: Stack.asm
Writes a range of memory to standard output in hexadecimal.
Call args:
ESI = starting offset
ECX = number of units
EBX = bytes/unit (1,2,or 4)
Return arg: None
Example: Dump a word array
.data array WORD 8,9,10,11,0FFFFh
mov esi,OFFSET array
mov ecx,LENGTHOF array ;5
mov ebx,TYPE array ;2
call DumpMem
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:
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.
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
Usually we want to:
But problems are…
Unpaired ops?
Less error-prone?
; do something
savedFlags DWORD ?
pop savedFlags
; do something
push savedFlags
Creating Procedures
Documenting Procedures
Example: SumOf Procedure
CALL and RET Instructions
Nested Procedure Calls
Local and Global Labels
Procedure Parameters
Flowchart Symbols
USES Operator
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
sample ENDP
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.
;———————————————————
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
SumOf ENDP
To call SumOf, prepare arguments: EAX, EBX, ECX
mov eax,10
mov ebx,20
mov ecx,30
call SumOf
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
00000020 call MySub
00000025 mov eax,ebx
MySub PROC
00000040 mov eax,edx
MySub ENDP
0000025 is the offset of the instruction immediately following the CALL instruction
00000040 is the offset of the first instruction inside MySub
The CALL instruction pushes 00000025 onto the stack, and loads 00000040 into EIP
(stack shown before RET executes)
Example: Stack.asm
The RET instruction pops 00000025 from the stack into EIP
200.unknown
By the time Sub3 is called, the stack contains all three return addresses:
202.unknown
203.unknown
jmp L2 ; error
L1:: ; global label
L2: ; local label
jmp L1 ; ok
A local label is visible only to statements inside the same procedure. A global label is visible everywhere.
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
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
ArraySum ENDP
The ArraySum procedure calculates the sum of an array. It makes two references to specific variable names:
This version of ArraySum returns the sum of any doubleword array whose address is in ESI. The sum is returned in EAX:
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
ArraySum ENDP
Lists the registers that will be preserved
ArraySum PROC USES esi ecx
mov eax,0 ; set the sum to zero
MASM generates the code shown in gray:
ArraySum PROC
ArraySum ENDP
SumOf PROC ; sum of three integers
push eax ; 1
add eax,ebx ; 2
add eax,ecx ; 3
pop eax ; 4
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):
What is a Link Library?
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 in the \Irvine\Examples\Lib32 folder.
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)
204.unknown
INCLUDE Irvine32.inc
mov eax,1234h ; input argument
call WriteHex ; show hex number
call Crlf ; end of line
Call each 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:
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
GetDateTime – Gets the current date and time from the system
GetMaxXY – Gets number of cols, rows in console window buffer
GetMseconds – Returns milliseconds elapsed since midnight
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
ReadDec – Reads 32-bit unsigned decimal integer from keyboard
ReadFromFile – Reads input disk file into buffer
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 stdin, terminated by [Enter]
SetTextColor – Sets foreground/background colors of all subsequent text output to the console
Str_compare – Compares two strings
Str_copy – Copies a source string to a destination string
Str_length – Returns the length of a string in EAX
Str_trim – Removes unwanted characters from a string.
Str_ucase – Converts a string to uppercase letters.
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
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
WriteStackFrame – Writes the current procedure’s stack frame to the console.
WriteStackFrameName – Writes the current procedure’s name and stack frame to the console.
WriteString – Writes null-terminated string to console window
WriteToFile – Writes buffer to output file
WriteWindowsMsg – Displays most recent error message generated by MS-Windows
A Windows help file showing:
Procedures
Procedure Purpose
Calling & Return Arguments
Example of usage
Directly look up procedures
examples\Lib32\Irvine32.asm
call Clrscr ; Clears console, locates cursor at upper left corner
mov eax,500
call Delay ; Pauses program execution for n millisecond interval
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:
str1 BYTE “Assembly language is easy!”,0
mov edx,OFFSET str1
call WriteString ; Writes null-terminated string to console window
call Crlf; Writes end of line sequence to standard output
Display a null-terminated string and move the cursor to the beginning of the next screen line.
str1 BYTE “Assembly language is easy!”,0Dh,0Ah,0
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)
IntVal = 35
mov eax,IntVal
call WriteBin ; display binary
call WriteDec ; display decimal
call WriteHex ; display hexadecimal
Display an unsigned integer in binary, decimal, and hexadecimal, each on a separate line.
Any potential problem?
0000 0000 0000 0000 0000 0000 0010 0011
Sample output:
fileName BYTE 80 DUP(0)
mov edx,OFFSET fileName
mov ecx,SIZEOF fileName – 1
call ReadString ; Reads string from stdin, terminated by [Enter]
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.
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.
str1 BYTE “Color output is easy!”,0
mov eax,yellow + (blue * 16)
call SetTextColor
mov edx,OFFSET str1
call WriteString
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.
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
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.
Clrscr ; clear screen
PromptForIntegers
WriteString ; display string
ReadInt ; input integer
ArraySum ; sum the integers
DisplaySum
WriteString ; display string
WriteInt ; display integer
gray indicates library procedure
205.unknown
RandomRange
Calculate the elapsed time of execution
Design procedures
Use push and pop to access the loop counter
Control the display position by calling Gotoxy
Performance Timing: TestLib3.asm
The Irvine64 Library
Calling 64-Bit Subroutines
The x64 Calling Convention
Crlf: Writes an end-of-line sequence to the console.
Random64: Generates a 64-bit pseudorandom integer.
Randomize: Seeds the random number generator with a unique value.
ReadInt64: Reads a 64-bit signed integer from the keyboard.
ReadString: Reads a string from the keyboard.
Str_compare: Compares two strings in the same way as the CMP instruction.
Str_copy: Copies a source string to a target location.
Str_length: Returns the length of a null-terminated string in RAX.
WriteInt64: Displays the contents in the RAX register as a 64-bit signed decimal integer.
WriteHex64: Displays the contents of the RAX register as a 64-bit hexadecimal integer.
WriteHexB: Displays the contents of the RAX register as an 8-bit hexadecimal integer .
WriteString: Displays a null-terminated ASCII string.
Place the first four parameters in registers
Add PROTO directives at the top of your program
ExitProcess PROTO ; located in the Windows API
WriteHex64 PROTO ; located in the Irvine64 library
Must use this with the 64-bit Windows API
CALl instruction subtracts 8 from RSP
First four parameters must be placed in RCX, RDX, R8, and R9
Caller must allocate at least 32 bytes of shadow space on the stack
When calling a subroutine, the stack pointer must be aligned on a 16-byte boundary.
See the CallProc_64.asm example program.
Procedure – named block of executable code
Runtime stack – LIFO structure
holds return addresses, parameters, local variables
PUSH – add value to stack
POP – remove value from stack
Use the Irvine32 library for all standard I/O and data conversion
(ret to main)
(ret to Sub1)
(ret to Sub2)
Your program
kernel32.lib
kernel32.dll
Irvine32.lib
can link to
Program (main)
PromptForIntegers
DisplaySum
WriteString
WriteString
程序代写 CS代考 加微信: powcoder QQ: 1823890830 Email: powcoder@163.com