Simple-Syscall-Implementation

Explanation

Firstly add the new syscall to the table of already existing syscalls in build/linux-5.xx.xx/arch/x86/entry/syscalls/syscall_64.tbl add

449 kern_2D_memcpy sys_kern_2D_memcpy

Then implement the same syscall in sys.c located at buiild/linux-5.xx.xx/kernal/sys.c

Where we define the following function

SYSCALL_DEFINE4(kern_2D_memcpy, float *, MAT1, float *, MAT2, int, ROW, int, COL)

We take the pointers to the two float matrices where MAT1 is the destination matrix and MAT2 is the source matrix. We create a new matrix of dimensions ROWxCOL in the kernel space to which we then copy the contents of MAT2 using copy_from_user and then we copy it to MAT1 using copy_to_user If any of the above are not possible we return -EFAULT else return 0 incase of success.

Building/Compiling the syscall

After adding the syscalls we need to run the following commands to configure our kernel

make

make modules_install

cp arch/x86_64/boot/bzImage /boot/vmlinuz-linux-5.15.4-gb0ccfee715-dirty

cp System-5.15.4.map System-5.15.4-gb0ccfee715-dirty.map

mkinitcpio -k 5.15.4-gb0ccfee715-dirty -g /boot/initramfs-linux-5.15.4-gb0ccfee715-dirty.img

grub-mkconfig -o /boot/grub/grub.cfg

reboot

Test the syscall

Make the test files in any directory and then run

gcc test.c -o test
./test