Invalid Argument error when using clone()

Question

I'm using this function call to clone()

clone (fun, (char*)stack + 0x500000, SIGCHLD | CLONE_FILES | CLONE_FS, arg);

where fun is a function: int fun(void*), stack = malloc (0x500000), and arg is of type void*.

I'm wondering what are some other possible causes for Invalid Argument perror.

I have checked stack is not NULL.

Answer 1

man clone:

  The  child_stack  argument  specifies the location of the stack used by
   the child process.  Since the child and calling process may share  mem‐
   ory,  it  is  not possible for the child process to execute in the same
   stack as the calling process.  The calling process must  therefore  set
   up memory space for the child stack and pass a pointer to this space to
   clone().  Stacks grow downward on all processors that run Linux (except
   the  HP  PA  processors),  so child_stack usually points to the topmost
   address of the memory space set up for the child stack.