System Calls

System calls

• https://en.wikipedia.org/wiki/System_call
• Programmatic way in which a computer program requests a service from the OS on which it is executed
• Number of System calls depends on:
  • Kernel Version (OS version)
  • Hardware Architecture (x86, x86_64, ARM)
• For x86_64/AMD64, ~450 system calls defined

Standard C Library

• It provides wrapper functions for system calls
• The library can be compiled for different architecture
• Windows ISO also needs to be downloaded based on architecture (x86_64 vs ARM)
• Linux
  • Library: glibc
  • URL: https://sourceware.org/git/?p=glibc.git;a=tree
  • Man page: https://man7.org/linux/man-pages/man2/syscalls.2.html
• MacOS
  • Library: Libc
  • URL: https://github.com/apple-open-source-mirror/Libc
• Windows
  • Library: UCRT (Universal C Runtime)
  • No public source code available
  • Can be found in Windows SDK

Process Control

• exec
• fork
• wait
• exit
• kill

File Management

• open
• read
• write
• close

Communication

• pipe

Event Related

• libraries:
  • libevent
  • libuv
• select, poll
• epoll — replacement for select and poll

strace

• It can be used to print system calls getting called internally

strace ls -al