this statement may fall through [-Werror=implicit-fallthrough=] 编译报错的解决方法

最新推荐文章于 2025-02-21 14:39:32 发布

随意的

最新推荐文章于 2025-02-21 14:39:32 发布

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分类专栏： GCC Makefile 文章标签： linux 驱动开发

本文链接：https://blog.youkuaiyun.com/daochukoukoiu/article/details/131303152

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报错log：

drivers/net/wireless/aic8800/aic8800_fdrv/rwnx_txq.c: In function 'rwnx_txq_vif_for_each_sta':
drivers/net/wireless/aic8800/aic8800_fdrv/rwnx_txq.c:642:12: error: this statement may fall through [-Werror=implicit-fallthrough=]
642 |   rwnx_vif = rwnx_vif->ap_vlan.master;
      |   ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/net/wireless/aic8800/aic8800_fdrv/rwnx_txq.c:643:2: note: here
643 | case NL80211_IFTYPE_AP:
      | ^~~~

源码报错位置：

    switch (RWNX_VIF_TYPE(rwnx_vif)) {
   case NL80211_IFTYPE_STATION:
   case NL80211_IFTYPE_P2P_CLIENT:
   {
       if (rwnx_vif->tdls_status == TDLS_LINK_ACTIVE)
           f(rwnx_vif->sta.tdls_sta, reason, rwnx_hw);
       if (!WARN_ON(rwnx_vif->sta.ap == NULL))
           f(rwnx_vif->sta.ap, reason, rwnx_hw);
       break;
   }
   case NL80211_IFTYPE_AP_VLAN:
       rwnx_vif = rwnx_vif->ap_vlan.master;
   case NL80211_IFTYPE_AP:
   case NL80211_IFTYPE_MESH_POINT:
   case NL80211_IFTYPE_P2P_GO:
   {
       struct rwnx_sta *sta;
       list_for_each_entry(sta, &rwnx_vif->ap.sta_list, list) {
           f(sta, reason, rwnx_hw);
       }
       break;
   }
   default:
       BUG();
       break;
   }

可以看到是code中的 case NL80211_IFTYPE_AP 没有break而发生警告

警告不会导致编译报错，但是编译参数中定义了 -Werror 从而导致编译报错

解决方法：

一、找到makefile中的-Werror，删除它

二、加入break（这可能不满足代码预期）

三、使用：GCC pragma #pragma GCC diagnostic ignored "-Wimplicit-fallthrough"，来禁用代码警告

如下示例（亲测有效）：

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wimplicit-fallthrough"

switch (RWNX_VIF_TYPE(rwnx_vif)) {
   case NL80211_IFTYPE_STATION:
   case NL80211_IFTYPE_P2P_CLIENT:
   {
       if (rwnx_vif->tdls_status == TDLS_LINK_ACTIVE)
           f(rwnx_vif->sta.tdls_sta, reason, rwnx_hw);
       if (!WARN_ON(rwnx_vif->sta.ap == NULL))
           f(rwnx_vif->sta.ap, reason, rwnx_hw);
       break;
   }
   case NL80211_IFTYPE_AP_VLAN:
       rwnx_vif = rwnx_vif->ap_vlan.master;
   case NL80211_IFTYPE_AP:
   case NL80211_IFTYPE_MESH_POINT:
   case NL80211_IFTYPE_P2P_GO:
   {
       struct rwnx_sta *sta;
       list_for_each_entry(sta, &rwnx_vif->ap.sta_list, list) {
           f(sta, reason, rwnx_hw);
       }
       break;
   }
   default:
       BUG();
       break;
   }
#pragma GCC diagnostic pop

注意：编译时，会在push和pop之间，禁用警告（此方法会导致此部分code调试困难，因为看不到警告）

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wimplicit-fallthrough"

//内容

#pragma GCC diagnostic pop

四、使用__attribute__((__fallthrough__))（亲测有效，且kernel中很多地方在用）;

在switch中不期望break的地方，加入__attribute__((__fallthrough__));

如下示例：

int main()
{
   enum nl80211_iftype ss = NL80211_IFTYPE_UNSPECIFIED;
   switch(ss){
       case NL80211_IFTYPE_UNSPECIFIED:
           printf("Hello, World! 11\n");
           __attribute__((__fallthrough__));
       case NL80211_IFTYPE_ADHOC:
           printf("Hello, World! 222\n");
       case NL80211_IFTYPE_STATION:
           printf("Hello, World! 33\n");
           break;
       default:
           printf("Hello, World! 55\n");
   }
   return 0;
}

kernel-5.10中，对此属性做了重定义，如下

kernel-5.10/include/linux/compiler_attributes.h

/*
* Add the pseudo keyword 'fallthrough' so case statement blocks
* must end with any of these keywords:
*   break;
*   fallthrough;
*   goto <label>;
*   return [expression];
*
* gcc: https://gcc.gnu.org/onlinedocs/gcc/Statement-Attributes.html#Statement-Attributes
*/
#if __has_attribute(__fallthrough__)
# define fallthrough                    __attribute__((__fallthrough__))
#else
# define fallthrough                    do {} while (0) /* fallthrough */
#endif