linux/lib/syscall.c
<<
>>
Prefs
   1#include <linux/ptrace.h>
   2#include <linux/sched.h>
   3#include <linux/export.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;
  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 */
  61int 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}
  86