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我现在正在使用 Linux 跟踪点进行练习。基本上，我正在尝试制作一个内核模块，其中定义了探测函数并将其连接到 Linux 内核中的跟踪点（内核源文件 dev.c 中的“trace_netif_receive_skb”）。当我在 SLES11 上编译并运行内核模块时，它运行良好。但是当我在 SLES12 上做同样的事情时，它抱怨符号未定义。内核模块源代码为：

  1 #include <linux/module.h>
  2 #include <linux/kernel.h>
  3 #include <linux/init.h>
  4 #include <linux/skbuff.h>
  5 #include <trace/events/net.h>
  6 
  7 static void probe(void *ignore, struct sk_buff *skb)
  8 {
  9     printk(KERN_INFO "probe, protocol[0X%04X]\n", ntohs(skb->protocol));
 10 }
 11 
 12 static int __init init_tracepoint(void)
 13 {
 14     if (0 != register_trace_netif_receive_skb(probe, NULL))
 15     {
 16         printk(KERN_INFO "tracepoint init fails\n");
 17     }
 18 
 19     printk(KERN_INFO "tracepoint init succeeds\n");
 20     return 0;
 21 }
 22 
 23 static void __exit cleanup_tracepoint(void)
 24 {
 25     unregister_trace_netif_receive_skb(probe, NULL);
 26     tracepoint_synchronize_unregister();
 27 
 28     printk(KERN_INFO "tracepoint exit\n");
 29 }
 30 
 31 module_init(init_tracepoint);
 32 module_exit(cleanup_tracepoint);
 33 
 34 MODULE_LICENSE("GPL");

这是SLES11上的输出，没有报错。

suse11-1:~/works/tracepoint # make
make -C /lib/modules/3.0.76-0.11-default/build M=/root/works/tracepoint modules
make[1]: Entering directory `/usr/src/linux-3.0.76-0.11-obj/x86_64/default'
make -C ../../../linux-3.0.76-0.11 O=/usr/src/linux-3.0.76-0.11-obj/x86_64/default/. modules
  CC [M]  /root/works/tracepoint/tracepoint.o
  Building modules, stage 2.
  MODPOST 1 modules
  CC      /root/works/tracepoint/tracepoint.mod.o
  LD [M]  /root/works/tracepoint/tracepoint.ko
make[1]: Leaving directory `/usr/src/linux-3.0.76-0.11-obj/x86_64/default'
suse11-1:~/works/tracepoint # insmod tracepoint.ko

这是 SLES12 上的输出，上面写着： WARNING: "__tracepoint_netif_receive_skb" [/root/works/codes/tracepoint/tracepoint.ko] undefined！我可以在 /var/log/messages 中找到“未知符号 __tracepoint_netif_receive_skb (err 0)”。

suse12-1:~/works/codes/tracepoint # make
make -C /lib/modules/4.4.21-69-default/build M=/root/works/codes/tracepoint modules
make[1]: Entering directory '/usr/src/linux-4.4.21-69-obj/x86_64/default'
  CC [M]  /root/works/codes/tracepoint/tracepoint.o
  Building modules, stage 2.
  MODPOST 1 modules
WARNING: "__tracepoint_netif_receive_skb" [/root/works/codes/tracepoint/tracepoint.ko] undefined!
  CC      /root/works/codes/tracepoint/tracepoint.mod.o
  LD [M]  /root/works/codes/tracepoint/tracepoint.ko
make[1]: Leaving directory '/usr/src/linux-4.4.21-69-obj/x86_64/default'
suse12-1:~/works/codes/tracepoint # 
suse12-1:~/works/codes/tracepoint # insmod tracepoint.ko 
insmod: ERROR: could not insert module tracepoint.ko: Unknown symbol in module

我检查了 SLES11 和 SLES12 的跟踪点框架的内核源代码，除非调用 EXPORT_TRACEPOINT_SYMBOL() 或 EXPORT_TRACEPOINT_SYMBOL_GPL()，否则不会导出定义的“__tracepoint_##name”“include/linux/tracepoint.h”，但我没有在 Linux 内核代码中找到调用 EXPORT_TRACEPOINT_SYMBOL(netif_receive_skb) 或 EXPORT_TRACEPOINT_SYMBOL_GPL(netif_receive_skb) 以导出符号 __tracepoint_netif_receive_skb 的任何地方。那为什么我在 SLES11 上没有遇到问题呢？我怎样才能让它在 SLES12 上工作？

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