Root/lib/syscall.c

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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