lib/syscall.c

   1 #include <linux/ptrace.h>
   2 #include <linux/sched.h>
   3 #include <linux/export.h>
   4 #include <asm/syscall.h>
   5
   6 static int collect_syscall(struct task_struct *target, long *callno,
   7                            unsigned long args[6], unsigned int maxargs,
   8                            unsigned long *sp, unsigned long *pc)
   9 {
  10         struct pt_regs *regs = task_pt_regs(target);
  11         if (unlikely(!regs))
  12                 return -EAGAIN;
  13
  14         *sp = user_stack_pointer(regs);
  15         *pc = instruction_pointer(regs);
  16
  17         *callno = syscall_get_nr(target, regs);
  18         if (*callno != -1L && maxargs > 0)
  19                 syscall_get_arguments(target, regs, 0, maxargs, args);
  20
  21         return 0;
  22 }
  23
  24 /**
  25  * task_current_syscall - Discover what a blocked task is doing.
  26  * @target:             thread to examine
  27  * @callno:             filled with system call number or -1
  28  * @args:               filled with @maxargs system call arguments
  29  * @maxargs:            number of elements in @args to fill
  30  * @sp:                 filled with user stack pointer
  31  * @pc:                 filled with user PC
  32  *
  33  * If @target is blocked in a system call, returns zero with *@callno
  34  * set to the the call's number and @args filled in with its arguments.
  35  * Registers not used for system call arguments may not be available and
  36  * it is not kosher to use &struct user_regset calls while the system
  37  * call is still in progress.  Note we may get this result if @target
  38  * has finished its system call but not yet returned to user mode, such
  39  * as when it's stopped for signal handling or syscall exit tracing.
  40  *
  41  * If @target is blocked in the kernel during a fault or exception,
  42  * returns zero with *@callno set to -1 and does not fill in @args.
  43  * If so, it's now safe to examine @target using &struct user_regset
  44  * get() calls as long as we're sure @target won't return to user mode.
  45  *
  46  * Returns -%EAGAIN if @target does not remain blocked.
  47  *
  48  * Returns -%EINVAL if @maxargs is too large (maximum is six).
  49  */
  50 int task_current_syscall(struct task_struct *target, long *callno,
  51                          unsigned long args[6], unsigned int maxargs,
  52                          unsigned long *sp, unsigned long *pc)
  53 {
  54         long state;
  55         unsigned long ncsw;
  56
  57         if (unlikely(maxargs > 6))
  58                 return -EINVAL;
  59
  60         if (target == current)
  61                 return collect_syscall(target, callno, args, maxargs, sp, pc);
  62
  63         state = target->state;
  64         if (unlikely(!state))
  65                 return -EAGAIN;
  66
  67         ncsw = wait_task_inactive(target, state);
  68         if (unlikely(!ncsw) ||
  69             unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
  70             unlikely(wait_task_inactive(target, state) != ncsw))
  71                 return -EAGAIN;
  72
  73         return 0;
  74 }
  75 EXPORT_SYMBOL_GPL(task_current_syscall);