Homework 1

Due date: January 18, 2006
Points: 100

1. (14 points) Text, problem 1.1.
2. (15 points) Text, problem 1.3.
3. (21 points) Text, problem 1.7.
4. (10 points) Text, problem 1.14.
5. (20 points) Handout, exercise 2.
6. (20 points) Consider the Linux system call lseek(2) . It changes the position of the offset of the file descriptor, so reading or writing after the call begins at the position indicated by the second and third arguments to lseek. On success, the function returns the new offset. On failure, it returns -1. But -1 is also a valid offset, representing a position of 0xffffffff. The manual page suggests using errno to distinguish between success and failure. Please describe in detail how to do this, and give sample code.

Extra Credit

1. (40 points) This exercise asks you to look at the standard I/O library for problems with robustness. Please write two programs that use functions from the strings library (the functions in that library are listed in the stdio(3) manual page on the Linux CSIF systems). You are to call the functions in such a way that they cause the library function to crash.
   To show that your program crashes the standard I/O function, use gdb(1) output to show that the crash occured within the library function. That is, the program must call the standard I/O library function, but cannot return from that call.
   Please explain why the library function fails. Support your hypothesis with references to the gdb output (or to source code, if that is available—but state how you know your version of the source code is the version actually installed!)
   Important note: you must supply the correct type of argument for the functions. You may not, for example, pass a character pointer where a file pointer is expected. Your two programs must not use the same technique to cause the crashes. For example, if you discover a certain argument to fread(3) causes a crash, you cannot use that same argument to cause a crash in fwrite(3) . However, if a different argument will cause fwrite(3) to crash, feel free to use that.