System Call: Create an exception that invokes an OS function

• Why exception? Because accessing external memory needs kernel-level permissions.
• Syscall Identifier: Numeric value indicating the operation
  • Kernel uses syscall table + identifier index to find the handler code
• Kernel must verify syscall arguments

Passing Parameters

x86 Syscall:

• Can pass 6 parameters through registers
• Pass the rest as a struct with pointer in the 6th register

Validating User Pointers: If a struct pointer is passed in, OS need to check if the calling process has access to the pointer