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;
  11
  12         if (!try_get_task_stack(target)) {
  13                 /* Task has no stack, so the task isn't in a syscall. */
  14                 *sp = *pc = 0;
  15                 *callno = -1;
  16                 return 0;
  17         }
  18
  19         regs = task_pt_regs(target);
  20         if (unlikely(!regs)) {
  21                 put_task_stack(target);
  22                 return -EAGAIN;
  23         }
  24
  25         *sp = user_stack_pointer(regs);
  26         *pc = instruction_pointer(regs);
  27
  28         *callno = syscall_get_nr(target, regs);
  29         if (*callno != -1L && maxargs > 0)
  30                 syscall_get_arguments(target, regs, 0, maxargs, args);
  31
  32         put_task_stack(target);
  33         return 0;
  34 }
  35
  36 /**
  37  * task_current_syscall - Discover what a blocked task is doing.
  38  * @target:             thread to examine
  39  * @callno:             filled with system call number or -1
  40  * @args:               filled with @maxargs system call arguments
  41  * @maxargs:            number of elements in @args to fill
  42  * @sp:                 filled with user stack pointer
  43  * @pc:                 filled with user PC
  44  *
  45  * If @target is blocked in a system call, returns zero with *@callno
  46  * set to the the call's number and @args filled in with its arguments.
  47  * Registers not used for system call arguments may not be available and
  48  * it is not kosher to use &struct user_regset calls while the system
  49  * call is still in progress.  Note we may get this result if @target
  50  * has finished its system call but not yet returned to user mode, such
  51  * as when it's stopped for signal handling or syscall exit tracing.
  52  *
  53  * If @target is blocked in the kernel during a fault or exception,
  54  * returns zero with *@callno set to -1 and does not fill in @args.
  55  * If so, it's now safe to examine @target using &struct user_regset
  56  * get() calls as long as we're sure @target won't return to user mode.
  57  *
  58  * Returns -%EAGAIN if @target does not remain blocked.
  59  *
  60  * Returns -%EINVAL if @maxargs is too large (maximum is six).
  61  */
  62 int task_current_syscall(struct task_struct *target, long *callno,
  63                          unsigned long args[6], unsigned int maxargs,
  64                          unsigned long *sp, unsigned long *pc)
  65 {
  66         long state;
  67         unsigned long ncsw;
  68
  69         if (unlikely(maxargs > 6))
  70                 return -EINVAL;
  71
  72         if (target == current)
  73                 return collect_syscall(target, callno, args, maxargs, sp, pc);
  74
  75         state = target->state;
  76         if (unlikely(!state))
  77                 return -EAGAIN;
  78
  79         ncsw = wait_task_inactive(target, state);
  80         if (unlikely(!ncsw) ||
  81             unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
  82             unlikely(wait_task_inactive(target, state) != ncsw))
  83                 return -EAGAIN;
  84
  85         return 0;
  86 }