Array Overflowing

Download arrayOverflowing.c, or copy it into your current directory on a CSE system by running

$ cp /web/cs1511/17s2/week07/files/arrayOverflowing.c .

In lectures we anticipated what would happen when you tried to inspect values of the index outside the array. Now try it out. Modify the code below to include a while loop so you can repeatedly test value without having to run the program multiple times.

Tip: You will need to use gcc for this activity, not dcc!

• Can you find where the canary variables are stored?
• Can you work out where and how gcc stores information in the frame for this function?
• [Does/How much does] the location of variables change if you run your program multiple times?
• What is the effect on the location of the variables of using/not using the -O flag when compiling with gcc?
• What else can you discover?

Start the activity - keep detailed lab notes about what you do, you code, what you find, and your thoughts. Submit this by creating a blog post.

Note: you may wish to write your notes and findings as you go in a text document using gedit, but make sure you post your findings in your blog when you’re finished.

int canaryA = 42;
int testArray[10] = {0,1,2,3,4,5,6,7,8,9};
int canaryB = 99;

int index;
printf ("Enter an array index between 0 and 9\n");
scanf ("%d", &index);
printf ("testArray[%d]=%d,\n",index, testArray[index]);

To run Styl-o-matic:

$ 1511 stylomatic arrayOverflowing.c
Looks good!

You’ll get advice if you need to make changes to your code.

Submit your work with the give command, like so:

$ give cs1511 wk07_arrayOverflowing

Or, if you are working from home, upload the relevant file(s) to the wk07_arrayOverflowing activity on Give Online.