This is just a brief description, so read at your own risk.
I have tested & used it. So it should be working. Please install a fresh install of Ubuntu.
This tutorial is for both 32 and 64 bit x86 processors and operating system. I have assumed that you are working in Ubuntu 10.10 and using kernel version 2.6.37.3 . If you are using any other kernel version just replace 2.6.37.3 with your version. I am also assuming you have extracted the source code.
Now let the new system call’s name be “add2″.
1. Now you will find a “arch” folder in the source code folder. Open the file arch/x86/kernel/syscall_table_32.S in a text editor. Go to the end of the document and add this line -
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.long sys_add2 /* my code */ |
2. Now open arch/x86/include/asm/unistd_32.h and find out
#define __NR_prlimit64 340
Add a new line after this:
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#define __NR_add2 341 |
Don’t just close yet. After 3-4 lines, you will find a line like
#define NR_syscalls 341
Change it to
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#define NR_syscalls 342 |
4. Now edit arch/x86/include/asm/unistd_64.h
Find out:
#define __NR_prlimit64 302
__SYSCALL(__NR_prlimit64, sys_prlimit64)
Now after these two lines, add these two lines
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#define __NR_add2 303 |
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__SYSCALL(__NR_add2, sys_add2) |
5. Now again in the source folder you will find a folder named include. Open the file include/linux/syscalls.h and go to the end of the file. Before the line
#endif
write this prototype definition line:
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asmlinkage long sys_add2(int i,int j); |
6. Now find out the kernel folder in the source directory. Create a new empty file in the kernel folder with the name “mysysteamcalls.c” . Add the following codes in the file:
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#include<linux/linkage.h> |
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asmlinkage long sys_add2(int i,int j) |
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{ |
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return i+j; |
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} |
7. Now open the Makefile in this folder(/kernel/Makefile) and find out
obj-y += groups.o
Add a new line before this line :
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obj-y += mysysteamcalls.o |
Ok, this is the edit you need to do to add a new system call. Now compile or recompile the source code and enjoy your new system call.
Important note: To add a new system call, you don’t need to create a new file, you can just add a new function in the same “mysysteamcalls.c” file. And if you don’t create a new file you don’t have to do the step 7.
-Enzam