Adding new system calls under ARM Linux-EEWORLD

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A recent project requires adding new system calls to the ARM Linux kernel to meet the needs of the project. So I searched on Google and Baidu, but the results were not satisfactory. I had to solve it myself! The steps to add are as follows (Note: I use the kernel 2.6.14.7, other versions are for readers to modify):

1. Open arch/arm/kernel/calls.S, find "#define NR_syscalls 328" and modify it. It should be noted that the number of system calls here must be increased by multiples of 4, otherwise the compilation will be wrong, for example: "#define NR_syscalls 332". Next, add the pointer of the system call function prototype, for example: .long sys_set_senda

2. Open include/asm-arm/unistd.h and add the macro of the system call number (I personally feel that this step can be omitted), for example:

#define __NR_plan_set_senda (__NR_SYSCALL_BASE+323)

The numbers here must be added in order. Otherwise, it will cause core operation errors.

3. Instantiate the system call, that is, write the implementation of the newly added system call. This is your job, for example:

asmlinkage long sys_set_senda(int iset)

{

if(iset)

UART_PUT_CR(&at91_port[2],AT91C_US_SENDA);

else

UART_PUT_CR(&at91_port[2],AT91C_US_RSTSTA);

return 0;

}

4. Open include/linux/syscalls.h and add function declaration

asmlinkage long sys_set_senda(int iset);

5. Calling the system call in the application

   int set_senda(int isset)
   {
      register long __r0 __asm__("r0") = (long)isset;
       register long __res __asm__("r0");
       __asm__ __volatile__ ( "swit" "0x900143" "nt" : "=r" ( __res) : "r" (__r0) : "lr");
       do { if ((unsigned long)(__res) >= (unsigned long)(-125))
               { errno = -(__res); __res = -1; }
               return (int) (__res);
       } while (0);
   }

6. End (Note: Readers are requested to study the case of multiple parameters on their own)

Keywords：ARM Reference address：Adding new system calls under ARM Linux

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