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#include <linux/ptrace.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <asm/syscall.h>

static int collect_syscall(struct task_struct *target, long *callno,
unsigned long args[6], unsigned int maxargs,
unsigned long *sp, unsigned long *pc)
{
struct pt_regs *regs = task_pt_regs(target);
if (unlikely(!regs))
return -EAGAIN;

*sp = user_stack_pointer(regs);
*pc = instruction_pointer(regs);

*callno = syscall_get_nr(target, regs);
if (*callno != -1L && maxargs > 0)
syscall_get_arguments(target, regs, 0, maxargs, args);

return 0;
}

/**
* task_current_syscall - Discover what a blocked task is doing.
* @target: thread to examine
* @callno: filled with system call number or -1
* @args: filled with @maxargs system call arguments
* @maxargs: number of elements in @args to fill
* @sp: filled with user stack pointer
* @pc: filled with user PC
*
* If @target is blocked in a system call, returns zero with *@callno
* set to the the call's number and @args filled in with its arguments.
* Registers not used for system call arguments may not be available and
* it is not kosher to use &struct user_regset calls while the system
* call is still in progress. Note we may get this result if @target
* has finished its system call but not yet returned to user mode, such
* as when it's stopped for signal handling or syscall exit tracing.
*
* If @target is blocked in the kernel during a fault or exception,
* returns zero with *@callno set to -1 and does not fill in @args.
* If so, it's now safe to examine @target using &struct user_regset
* get() calls as long as we're sure @target won't return to user mode.
*
* Returns -%EAGAIN if @target does not remain blocked.
*
* Returns -%EINVAL if @maxargs is too large (maximum is six).
*/
int task_current_syscall(struct task_struct *target, long *callno,
unsigned long args[6], unsigned int maxargs,
unsigned long *sp, unsigned long *pc)
{
long state;
unsigned long ncsw;

if (unlikely(maxargs > 6))
return -EINVAL;

if (target == current)
return collect_syscall(target, callno, args, maxargs, sp, pc);

state = target->state;
if (unlikely(!state))
return -EAGAIN;

ncsw = wait_task_inactive(target, state);
if (unlikely(!ncsw) ||
unlikely(collect_syscall(target, callno, args, maxargs, sp, pc)) ||
unlikely(wait_task_inactive(target, state) != ncsw))
return -EAGAIN;

return 0;
}
EXPORT_SYMBOL_GPL(task_current_syscall);
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