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Nachos Assignment#1

Nachos Assignment#1. System calls implementation. What are system calls?. Enable you to interact with OS kernel. A switch from User Mode to Kernel Mode. How does it work?(1). How does it work?(2). How does it work?(3). test/start.s. MIPS dependend assembler code for userlevel bindings

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Nachos Assignment#1

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  1. Nachos Assignment#1 System calls implementation

  2. What are system calls? • Enable you to interact with OS kernel. • A switch from User Mode to Kernel Mode

  3. How does it work?(1)

  4. How does it work?(2)

  5. How does it work?(3)

  6. test/start.s • MIPS dependend assembler code for userlevel bindings • Do not modify! • How does it work: • gets parameter via registers (C-calling convention) • loads syscall number into first register • does a syscall exception (enter the kernel) • jump back

  7. What are you going to do? • Implement following system calls. • Create : Create a file with the “filename” • Open : Open a file with the “filename” • Read : Read from the file or console • Write : Write to the file or console • Close : Close the opened file with the”fid”

  8. Related Nachos codes (1) • syscall.h • Definitions of the system call prototypes • You have to implement it. • exception.cc • The handler for system calls and other exceptions is here.

  9. Related Nachos codes (2) • test/start.s • Assembly startup code of every user program of nachos. • To see how a user program does a system call and enters the kernel.

  10. What are Stubs for ?(1) • Each system call has a stub associated with it. • Assembly codes used to ： • assist user programs to understand system calls. • Make system calls to kernels.

  11. What are Stubs for ?(2) • Register r2 stores the system call number. • Other arguments in r4,r5,r6,r7,respectly. • New system call need a new stub to be added in “start.s”. (No need to do it in this project)

  12. Implementation example: • void Create(char* filename) • Crates a file with the name”filename” given as the parameter.

  13. Implementation example: • Add your code in exception.cc. • ReadRegister -> machine.cc • To get the starting virtual address. • ReadMem -> translate.cc • Translate virtual address to real address

  14. Setup your tool • On your PC • Get the tar ball from our site and untar it under “/”. • Go to [Install Dir]/NachOS-4.0/coff2noff/ compile it with makefile. • On IM workstation • Go to [Install Dir]/NachOS-4.0/coff2noff/ compile it with makefile.

  15. Compiling step • Add the file in the “Makefile” under “build.linux” • Add the test file in the “Makefile” under “nachos/code/test”. • Complile test file under “test”,others under “nachos/code/build.linux”

  16. Project grading policy • Primary requirement • System call implementation :70% • Documentation :15% • How to verify your work?:15% • Demo: • About 5 groups will be chosen to demo.

  17. Project Deadline • 4/30 24:00 • E-mail your project to r91050@im.ntu.edu.tw • Use student id as file name.(one of the two group member) Ex:R91725050

  18. Your files SHOULD include: • Modified files and test files • 5 page-report • Do not put source code in your report. • Explain why you chose to modify these files. • Problems encountered and your solution • Anything else.

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