Clicker Questions - 14-Memory
We are running a program, and when we look at its entry in /proc, we see:
00010000-00011000 r-xp 00000000 00:22 126617690 /home/plank/a.out
00020000-00021000 rw-p 00000000 00:22 126617690 /home/plank/a.out
012cb000-012ec000 rw-p 00000000 00:00 0 [heap]
76f3a000-76f3b000 r--p 0001f000 b3:07 524429 /lib/arm-linux-gnueabihf/ld-2.19.so
76f3b000-76f3c000 rw-p 00020000 b3:07 524429 /lib/arm-linux-gnueabihf/ld-2.19.so
7ebc3000-7ebe4000 rwxp 00000000 00:00 0 [stack]
The program prints the return value of getpagesize(), and it is 4096 (0x1000).
Question 1: Your program has a procedure called proc(). What is the smallest address greater than or equal to proc that will segfault when you try to read it? You can give an absolute address or a value relative to proc.
Answer
0x11000. -- this is the first address on the next page.Question 2: What is the smallest address greater than or equal to proc that will segfault when you try to write it? You can give an absolute address or a value relative to proc.
Answer
proc. Since the code (text) segment disallows writes, trying to write any address in the code segment will cause a segmentation violation.Question 3: Can &edata be equal to 0x10f00? (Answer Yes or No).
Answer
No -- &edata is in the globals (data) segment, which is between0x20000 and 0x21000. Note it is protected as read/write.
Question 4: Can &etext be equal to 0x10f00? (Answer Yes or No).
Answer
Yes -- &etext is in the code (text) segment.Question 5: How many pages are in the heap (you can answer in hex or decimal)?
Answer
The addresses of the heap are0x12cb000-0x12ec000. That means 00x12ec-0x12cb = 0x21 pages. In decimal, that's 33.
Question 6: If I make enough procedure calls, the beginning of the stack, as reported by the entry in /proc, will be changed to some number smaller than 0x7ebc3000. (Answer T or F)