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System Calls: From User to Kernel Interaction

Learn the detailed process of system calls from user space back to the kernel in assembly language. Discover the mapping from syscall number to C functions, handling user space data transfers, and funky kernel programming techniques. Explore global variables, static allocation, and avoiding magic numbers. Is kmalloc the solution?

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System Calls: From User to Kernel Interaction

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  1. System calls • What’s the exact process from user back to user? 451shell% physusage • In shell: ... syscall(__NR_physusage, ...) ...

  2. System calls, cont’d • In assembly: int $0x01 • Says: switch to kernel and tell it to call system call 01 • Kernel needs mapping from syscall number to backing C function

  3. System calls, cont’d • C function executes • May copy to/from user space • Return

  4. Funky kernel programming • Global variables • primary.c int array[2] = {1, 2}; • secondary.c extern int array[]; • Static allocation • No magic numbers, please • Hmm, kmalloc?

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