GATE CS 2005 Q72 — System Calls

When a process calls fork(), a duplicate child process is created. The execution behavior of the parent and child is determined by the return value of fork():

• In the child process: fork() returns 0. The if block is executed.
  • Value printed ($x$): $x = a_{\text{initial}} + 5$
  • Address printed ($y$): $y = \&a$
• In the parent process: fork() returns the non-zero PID of the child. The else block is executed.
  • Value printed ($u$): $u = a_{\text{initial}} - 5$
  • Address printed ($v$): $v = \&a$

1. Relationship between $u$ and $x$:

$$x - u = (a_{\text{initial}} + 5) - (a_{\text{initial}} - 5) = 10 \implies u + 10 = x$$

2. Relationship between $v$ and $y$:

During a fork(), the child process gets an exact duplicate of the parent's address space. This means the virtual address of the variable a is identical in both the parent and child processes.

Since the printf function prints the virtual address of the variable (using the %p format specifier), the printed address will be the same in both processes. Therefore, $v = y$.

Thus, the correct statement is $u + 10 = x \text{ and } v = y$.