Change in compiling methods for linux system calls

In the 2.6 era, the steps for writing a linux system call are as follows:

1. Compile the actual operation function
2. Add macro definitions in linux/include/asm-i386/unistd. h

   #define __NR_myfunctioin 399

3. In linux/arch/i386/kernel/entry. S, add

   .long SYMBOL_NAME(myfunction)

4. Compile the kernel
5. Use _ syscall [1-6] (type, name, type, arg1) to call

The corresponding macro definition file cannot be found at the corresponding location of the kernel in the latest version.

Unistd. modify the H file to reference the 32-bit and 64-bit versions respectively, and placed in/arch/x86/include/uapi/asm/unistd _ [32 | 64 | x32]. h. arm is stored in/arch/arm/uapi/asm/unistd. h, the other architectures are similar.

In addition, some files are modified to the _ SYSCALL (n, call) method definition.

The sys_call_table definition in the entry. S file is also placed in the syscall. h file, and the original assembly is modified to the definition method of the C array.

_ SYSCALL is a macro.

#define __SYSCALL(n, call) [nr] = (call),#define __SYSCALL_XX(n, sym, compat)

In addition, the sys_call_table [nr_syscils] array is added.

void *sys_call_table[NR_syscalls] = {    [0 ... NR_syscalls-1] =  sys_ni_syscall,#include <asm/unistd.h>}

Currently, there are two ways in the kernel to define system calls: macro-defined numbers and _ SYSCALL.