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                 *callno = -1;
  15                 return 0;
  16         }
  17
  18         regs = task_pt_regs(target);
  19         if (unlikely(!regs)) {
  20                 put_task_stack(target);
  21                 return -EAGAIN;
  22         }
  23
  24         *sp = user_stack_pointer(regs);
  25         *pc = instruction_pointer(regs);
  26
  27         *callno = syscall_get_nr(target, regs);
  28         if (*callno != -1L && maxargs > 0)
  29                 syscall_get_arguments(target, regs, 0, maxargs, args);
  30
  31         put_task_stack(target);
  32         return 0;
  33 }
  34
  35 /**
  36  * task_current_syscall - Discover what a blocked task is doing.
  37  * @target:             thread to examine
  38  * @callno:             filled with system call number or -1
  39  * @args:               filled with @maxargs system call arguments
  40  * @maxargs:            number of elements in @args to fill
  41  * @sp:                 filled with user stack pointer
  42  * @pc:                 filled with user PC
  43  *
  44  * If @target is blocked in a system call, returns zero with *@callno
  45  * set to the the call's number and @args filled in with its arguments.
  46  * Registers not used for system call arguments may not be available and
  47  * it is not kosher to use &struct user_regset calls while the system
  48  * call is still in progress.  Note we may get this result if @target
  49  * has finished its system call but not yet returned to user mode, such
  50  * as when it's stopped for signal handling or syscall exit tracing.
  51  *
  52  * If @target is blocked in the kernel during a fault or exception,
  53  * returns zero with *@callno set to -1 and does not fill in @args.
  54  * If so, it's now safe to examine @target using &struct user_regset
  55  * get() calls as long as we're sure @target won't return to user mode.
  56  *
  57  * Returns -%EAGAIN if @target does not remain blocked.
  58  *
  59  * Returns -%EINVAL if @maxargs is too large (maximum is six).
  60  */
  61 int task_current_syscall(struct task_struct *target, long *callno,
  62                          unsigned long args[6], unsigned int maxargs,
  63                          unsigned long *sp, unsigned long *pc)
  64 {
  65         long state;
  66         unsigned long ncsw;
  67
  68         if (unlikely(maxargs > 6))
  69                 return -EINVAL;
  70
  71         if (target == current)
  72                 return collect_syscall(target, callno, args, maxargs, sp, pc);
  73
  74         state = target->state;
  75         if (unlikely(!state))
  76                 return -EAGAIN;
  77
  78         ncsw = wait_task_inactive(target, state);
  79         if (unlikely(!ncsw) ||
  80             unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
  81             unlikely(wait_task_inactive(target, state) != ncsw))
  82                 return -EAGAIN;
  83
  84         return 0;
  85 }