Unix foundations

Invoking a New Program

• Process address space
• Text: code
• Initialized data:
• Uninitialized data(bss):
• Shared memory(SV):
• Shared libraries:
• Heap: dynamic space
• User stack: space allocated by the kernel

exec System Call

• Parse & access
• Verify the permission
• Read the header and check if valid executable
• If the file has SUID or SGID bits set in its mode, change the caller’s effective UID or GID to that of the owner
• Copy the arguments to exec and the env. variables into kernel.
• Allocate swap space for the data and stack region
• Set up the new address space.
• Copy the arguments and env. variables back onto the new user stack.
• Reset all signal handlers to default actions.
• Initialize the hardware context.