Introduction To Algorithms, Third Edition (international Edition)
3rd Edition
ISBN: 9780262533058
Author: Thomas H. Cormen, Charles E. Leiserson, Ronald L. Rivest, Clifford Stein
Publisher: TRILITERAL
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Chapter 8.1, Problem 1E
Program Plan Intro
To find the smallest possible depth of a leaf in a decision tree for a comparison sort.
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Students have asked these similar questions
Returns an US standard formatted phone number, in the format of
(xxx) xxx-xxxx
the AreaCode, Prefix and number being each part in order.
Testing Hint: We be exact on the format of the number when
testing this method. Make sure you think about how to convert
33 to 033 or numbers like that when setting your string format. Reminder
the %02d - requires the length to be 2, with 0 padding at the front if a single
digit number is passed in.
The next problem concerns the following C code:
/copy input string x to buf */
void foo (char *x) {
char buf [8];
strcpy((char *) buf, x);
}
void callfoo() {
}
foo("ZYXWVUTSRQPONMLKJIHGFEDCBA");
Here is the corresponding machine code on a Linux/x86 machine:
0000000000400530 :
400530:
48 83 ec 18
sub
$0x18,%rsp
400534:
48 89 fe
mov
%rdi, %rsi
400537:
48 89 e7
mov
%rsp,%rdi
40053a:
e8 d1 fe ff ff
40053f:
48 83 c4 18
add
callq 400410
$0x18,%rsp
400543:
c3
retq
0000000000400544 :
400544:
48 83 ec 08
sub
$0x8,%rsp
400548:
bf 00 06 40 00
mov
$0x400600,%edi
40054d:
e8 de ff ff ff
callq 400530
400552:
48 83 c4 08
add
$0x8,%rsp
400556:
c3
This problem tests your understanding of the program stack. Here are some notes to
help you work the problem:
• strcpy(char *dst, char *src) copies the string at address src (including
the terminating '\0' character) to address dst. It does not check the size of
the destination buffer.
You will need to know the hex values of the following characters:
A ROP (Return-Oriented Programming) attack can be used to execute arbitrary
instructions by chaining together small pieces of code called "gadgets." Your goal is
to create a stack layout for a ROP attack that calls a function located at '0x4018bd3'.
Below is the assembly code for the function 'getbuf', which allocates 8 bytes of stack
space for a 'char' array. This array is then passed to the 'gets' function. Additionally,
you are provided with five useful gadgets and their addresses. Use these gadgets to
construct the stack layout.
Assembly for getbuf
1 getbuf:
2
sub
$8, %rsp
3
mov
%rsp, %rdi
4
call
gets
56
add
$8, %rsp
ret
#Allocate 8 bytes for buffer
#Load buffer address into %rdi
#Call gets with buffer
#Restore the stack pointer
#Return to caller.
Stack
Layout
(fill
in
Gadgets
each
8-byte
section)
Address
Gadget
Address
Value (8 bytes)
0x4006a7 pop %rdi; ret
0x7fffffffdfc0
Ox4006a9 pop %rsi; ret
0x7fffffffdfb8
0x4006ab pop %rax; ret
0x7fffffffdfb0
0x7fffffffdfa8
Ox4006ad mov %rax,…
Chapter 8 Solutions
Introduction To Algorithms, Third Edition (international Edition)
Knowledge Booster
Similar questions
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