linux/lib/syscall.c
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   1#include <linux/ptrace.h>
   2#include <linux/sched.h>
   3#include <linux/module.h>
   4#include <asm/syscall.h>
   5
   6static 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 */
  50int 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}
  75EXPORT_SYMBOL_GPL(task_current_syscall);
  76
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