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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

Case in Point: LLinux [Härtig et al. 97]

• Port of Linux kernel to L4 (like Mach Unix server)
  • single-threaded (for simplicity, not performance)
  • is pager of all Linux user processes
  • maps emulation library and signal-handling code into AS
  • server AS maps physical memory (& Linux runs within)
  • copying between user and server done on physical memory
    • use software lookup of page tables for address translation
• Changes to Linux restricted to architecture-dependent part
• Duplication of page tables (L4 and Linux server)
• Binary compatible to native Linux via trampoline mechanism
  • but also modified libc with RPC stubs

Signal delivery in LLinux

• separate signal-handler thread in each user process
  • server IPCs signal-handler thread
  • handler thread ex_regs main user thread to save state
  • user thread IPCs Linux server
  • server does signal processing
  • server IPCs user thread to resume