Add a system call in MIPS Linux. Take Linux kernel 2.6.18 as an example.

To add a system call, follow these steps:
1. Add your system call entry to the system call table sys_call_table of the kernel.

Select the file to be modified based on the number of kernel bits (32/64 bits:
ARCH/MIPS/kernel/scall32-o32.S ------> 32bit Kernel
ARCH/MIPS/kernel/scall64-64.S ------> 64bit Kernel

64bit kernel, if compatible with 32 bit Abi (o32, n32), you also need to modify scall64-o32.S or scall64-n32.S
Taking 32bit kernel as an example, find macro definition in arch/MIPS/kernel/scall32-o32.S

. Macro syscalltable/* system call number starting from 4000 */
......
......
Sys sys_faccessat 3/* 4300 */
Sys sys_pselect6 6
Sys sys_ppoll 5
Sys sys_unshare 1
Sys sys_splice 4
Sys sys_sync_file_range 7/* 4305 */
Sys sys_tee 4
Sys sys_vmsplice 4
Sys sys_move_pages 6
Sys sys_set_robust_list 2
Sys sys_get_robust_list 3/* 4310 */
Sys sys_ni_syscall 0
Sys sys_ni_syscall 0
Sys sys_ni_syscall 0
Sys sys_ioprio_set 3
Sys sys_ioprio_get 2/* 4315 */
Sys sys_wenxy_test 0/* system call ID is 4316, wenxy add, 20091120 */
. Endm
......

Finally, the custom system call sys_wenxy_test is added to sys_call_table, and sys is used as a helper macro. The value 0 after the call name indicates the number of parameters required for the system call.

It can only be added at the end of sys_call_table. Otherwise, standard system calls will be disrupted.

2. Implement system calls

You can provide an implementation in arch/MIPS/kernel/syscall. C, for example:
......
/* Wenxy add begin, 20091119, A.M .*/
# Include "/opt/bcm97405/kernel/stblinux-2.6.18/ARCH/MIPS/SiByte/CFE/cfe_api.h"
Asmlinkage int sys_wenxy_test (void)
{
Uint64_t cfe_ept, cfe_handle;
Int N;
// N = cfe_init (cfe_handle, cfe_ept );

Printk (kern_emerg "kernel, wenxy Debug: into [% s], call [% s ()]/n", _ file __, _ function __);
Return 100;
}
/* Wenxy add end */

3. Modify include/ASM-MIPS/unistd. h.

Modify the macro definition based on your kernel bit and the supported Abi version. Modify the 32bit kernel:

# DEFINE _ nr_linux_syscils 320 ---------> 321 (the number of Linux syscils)
# DEFINE _ nr_o32_linux_syscils 320 ---------> 321 (the number of Linux o32 syscils)

Add the corresponding macro set to the end:
.......
# DEFINE _ nr_ppoll (_ nr_linux ++ 302)
# DEFINE _ nr_unshare (_ nr_linux ++ 303)
# DEFINE _ nr_splice (_ nr_linux ++ 304)
# DEFINE _ nr_sync_file_range (_ nr_linux + 305)
# DEFINE _ nr_tee (_ nr_linux ++ 306)
# DEFINE _ nr_vmsplice (_ nr_linux + 307)
# DEFINE _ nr_move_pages (_ nr_linux + 308)
# DEFINE _ nr_set_robust_list (_ nr_linux + 309)
# DEFINE _ nr_get_robust_list (_ nr_linux + 310)
# DEFINE _ nr_ioprio_set (_ nr_linux + 314)
# DEFINE _ nr_ioprio_get (_ nr_linux + 315)

/* Wenxy add begin, 20091119, A.M .*/
# DEFINE _ nr_wenxy_test (_ nr_linux + 316)
/* Wenxy add end */

......

4. test the new system call wenxy_test
Test. c file, C program:
# If 1
# Include <stdio. h>
# Include <Linux/unistd. h>
# Include <sys/syscall. h>
# Include <errno. h>
# Else
# Include "/opt/bcm97405/kernel/stblinux-2.6.18/include/Linux/unistd. H"
# Include "/opt/bcm97405/kernel/stblinux-2.6.18/include/sys/syscall. H"
# Endif

// # DEFINE _ nr_getjiffies 320
// # DEFINE _ nr_wenxy_test 319
# DEFINE _ nr_wenxy_test (_ nr_linux + 316)

_ Syscall0 (INT, wenxy_test );

Int main ()
{
Long jiffies;
Int N;
// Jiffies = syscall (_ nr_getjiffies );

// Printf ("Current jiffies is % LX/N", jiffies );

N = 0;
// N = syscall (_ nr_wenxy_test );
N = wenxy_test ();
Printf ("wenxy: syscall return value is [% d], system call ID = [% d]/n", N, _ nr_wenxy_test );

Return 0;
}
Command for compiling test. C: mipsel-Linux-gcc-I/opt/bcm97405/kernel/stblinux-2.6.18 test. c

Or write the assembler yourself:
Run the following program to test the re-compiled kernel:

. Text
. Globl main
. Ent main

Main:

Li $2, 4316/* system call number of wenxy_test */
Syscall

. End main

The system call convention in MIPs is as follows:

V0: used to set the system call number
A0 ~ A3: set the first four parameters.
Syscall System Call trigger command

Compile GCC cat. S-o a. Out

Run./A. Out

Correct output should be as follows:
# A. Out
Kernel, wenxy Debug: into [ARCH/MIPS/kernel/syscall. C], call [sys_wenxy_test ()]
Wenxy: syscall return value is [100], system call ID = [4316]

PS.
A. You can use dmesg to view kernel logs or use strace a. Out to track system call Information.
B. References:
Http://www.ibm.com/developerworks/cn/linux/l-system-calls/index.html
Http://www.diybl.com/course/3_program/hb/hbjs/200798/70400.html #