Adding syscall¶

An example of adding a system call is conducted based on the threadsinfo syscall. The procedure should be performed as follows:

Add syscall’s declaration in libphoenix, e.g. libphoenix/inlude/sys/threads.h:
```
extern int threadsinfo(int n, threadinfo_t *info);
```
Update the syscall list in phoenix-rtos-kernel/include/syscalls.h. It is recommended to insert a new syscall at the end of the list:
```
ID(threadsinfo) \
```

Create a syscall handler in phoenix-rtos-kernel/syscalls.c:

int syscalls_threadsinfo(void *ustack)
{
    int n, i;
    pid_t ppid;
    threadinfo_t *info;

    /* Get input arguments from stack according to order in the syscall prototype.
        GETFROMSTACK macro modifies value of stack pointer. The order of its invocation has to be compliant with arguments put on stack.
        GETFROMSTACK arguments:
        1st arg - stack pointer
        2nd arg - type of data put on stack
        3rd arg - variable name
        4th arg - id order on stack (start from 0) */
    GETFROMSTACK(ustack, int, n, 0);
    GETFROMSTACK(ustack, threadinfo_t *, info, 1);

    /* Get thread's list from kernel's submodule */
    n = proc_threadsList(n, info);

    /* Assign parent process id */
    for (i = 0; i < n; ++i) {
        if ((ppid = posix_getppid(info[i].pid)) > 0)
            info[i].ppid = ppid;
    }

    return n;
}

The system call can be invoked in user application by including sys/threads.h header. This example syscall is used by the ps applet in the psh (Phoenix-Shell).