What is System call?
The mechanism by which applications ask the OS for services such as file I/O or memory allocation. A dedicated instruction raises an exception that switches to privileged mode and invokes the kernel.
Field: OS & Hardware
System call in the explanations
Every system call requires switching from user to privileged mode, saving registers, checking arguments and returning, a fixed cost paid even for a single byte.
When writing small data one byte at a time, why is accumula…The kernel identifies the system call by the number in a7, uses a0–a2 as arguments, returns the result and goes back to user mode.
What happens when the ecall instruction at the end of the R…It is the same mechanism as demand paging, avoiding a system call per read and reducing extra data copies.
In a mechanism that maps a file into memory (such as mmap),…
Questions that mention System call (4)
- When writing small data one byte at a time, why is accumulating it in a user-space buffer and writing in bulk faster than calling a system call each time?
- What happens when the ecall instruction at the end of the RISC-V code above executes?
- In a mechanism that maps a file into memory (such as mmap), what happens when the file's contents are read?
- What is the idea behind KPTI (kernel page-table isolation), introduced as a software countermeasure to Meltdown?
Related terms
Privileged mode TLB (translation lookaside buffer) Entry point Interrupt Page fault Demand paging Kernel page-table isolation (KPTI) Meltdown ASID Context switch