How to add system calls to OS/161
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This document provides instructions for adding system calls to the OS/161 project, focusing on the implementation of the sys_getpid() system call. It guides through configuration, creation of syscall implementation files, updating necessary configurations, and testing the implemented system call through a user program. The process includes specific commands and coding examples to facilitate building and testing the kernel with new system calls.
How to add system calls to OS/161
- 1. 1 COMP 3500 Introduction to Operating Systems Project 4 – Processes and System Calls Part 3: Adding System Calls to OS/161 Dr. Xiao Qin Auburn University http://www.eng.auburn.edu/~xqin xqin@auburn.edu
- 2. Use System Call: sys_reboot() In src/sbin/reboot/reboot.c How to run the reboot program? Type “p /sbin/reboot”
- 3. Use System Call: sys_reboot() Another Example: In src/sbin/poweroff/poweroff.c How to run the poweroff program? Type “p /sbin/poweroff”
- 4. System Call: sys_reboot() In src/kern/include/syscall.h
- 5. 5
- 6. Which function calls mips_syscall()? 6 exception.S mips_trap() mips_syscall() See cs161/kern/arch/mips/mips
- 7. Which function calls exception.S? • A user program 7 – Loads a system call code into register $v0 – Loads the arguments into registers $a0, ..., $a3 • System calls that return values – Put their result in register $v0
- 8. Using cs161-gdb to trace sys_reboot()? b sys_reboot type “p /sbin/reboot” at the OS161 menu prompt bt (back trace) 8
- 9. User-Level Interface for System Calls src/include/unistd.h • This file contains the user-level interface definition of the system calls for OS/161 • Note that the user-level interface defined in unistd.h is different from that of the kernel functions that you will define to implement these calls. • You need to declare the kernel functions in kern/include/syscall.h
- 10. Step 1: Configuration • Configure the source code tree %cd ~/cs161/src %./configure • Configure a kernel named ASST2 %cd ~/cs161/src/kern/conf %./config ASST2
- 11. Step 2: System Call Implementation • 2.1 Create a System Call Implementation File ~/cs161/src/kern/userprog
- 12. Step 2.1: System Call Implementation • Example: getpid_syscall.c #include <types.h> #include <syscall.h> #include <thread.h> #include <curthread.h> /* Sample implementation of sys_getpid() */ int sys_getpid(pid_t *retval) { *retval = curthread->t_pid; return 0; }
- 13. Step 2.1: System Call Implementation • Update struct thread in kern/include/thread.h by adding the following data item: pid_t t_pid;
- 14. Step 2.2: Update Configuration File and Reconfigure the Project • Now you can update the configuration file (i.e., conf.kern) located in src/kern/conf • The following line should be added: file userprog/getpid_syscall.c • Reconfigure the project (see Step 1 for details)
- 15. Step 2.3: Update Configuration File and Reconfigure the Project • The prototype of sys_getpid may be included in the following file: ~/cs161/src/kern/include/syscall.h • Add the following function prototype in the above file: int sys_getpid(pid_t *retval);
- 16. Step 2.4: Update the system call handler syscall.c • The system call handler syscall.c is located in the following directory: ~/cs161/src/kern/arch/mips/mips • Add the following segment in the switch-case statement of the mips_syscall() function in syscall.c case SYS_getpid: err = sys_getpid(&retval); break;
- 17. Step 2.5: Rebuild the OS/161 Kernel • Follow the commands below to rebuild the kernel. %cd ~/cs161/src/kern/compile/ASST2 %make depend %make %make install
- 18. Step 3: Test System Calls • Step 3.1 Create a User Program for the New System Call • Step 3.2 Run the User Program in OS/161
- 19. Step 3.1-1 Create a new directory using forktest as a template • We place all the test programs in the following directory: ~/cs161/src/testbin • Each test program and its associated files (e.g., Makefile) are organized in a dedicated directory. • Create a new directory using forktest as a template %cd ~/cs161/src/testbin %cp –r forktest getpidtest
- 20. Step 3.1-2 Change source code name %cd getpidtest %mv forktest.c getpidtest.c
- 21. Step 3.1-3 Modify getpidtest.c #include <unistd.h> #include <stdio.h> int main() { int mypid; mypid = getpid(); reboot(RB_REBOOT); return 0; }
- 22. Step 3.1-4 Modify Makefile and depend.mk • Modify Makefile and depend.mk by replacing forktest with getpidtest
- 23. Step 3.1-5 Compile getpidtest.c • Compile getpidtest.c using cs161-gcc. This can be done through running Makefile as below. %make • The make utility program compile getpidtest.c and generate an execute file called getpidtest
- 24. Step 3.1-6 Copy the executable file to the root directory • Copy the executable file getpidtest into ~/cs161/root/testbin %cp getpidtest ~/cs161/root/testbin/getpidtest • The above executable file will be loaded by OS/161 through the p command in the main menu.
- 25. Step 3.2 Run the User Program in OS/161 • You can follow the instructions below to run the testing program created in Step 3.1: %cd ~/cs161/root %./sys161 kernel • In the menu prompt type: p /testbin/getpidtest
Editor's Notes
- #7: mips_trap() and mips_syscall() can be found in cs161/kern/arch/mips/mips