c - getifaddrs() 函数处理结果导致段错误

Question

我尝试使用 official getifaddrs page 中的示例在 Ubuntu 18.04.5 LTS 仿生(Odroid-N2 board ARM64)上出现段错误。
进一步分析表明，由 getifaddrs() 填充的 struct ifaddrs 包含无效指针。
这是我的代码:

#include <stdint.h>
#include <unistd.h>
#include <ifaddrs.h>

int main(int argc, char** argv) {
    struct ifaddrs *ifaddr;
    int family;
    
    if (getifaddrs(&ifaddr) == -1) {
        perror("getifaddrs");
        return -1;
    }
    
    
    for (struct ifaddrs *ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
        if (ifa->ifa_addr == NULL)
            continue;
            
        printf("IF: %s\n",ifa->ifa_name);           
        printf("\tThis: %p\n", ifa);
        printf("\tNext: %p\n", ifa->ifa_next);
        printf("\tFlags: %x\n",ifa->ifa_flags);
        printf("\tAddr: %p\n", ifa->ifa_addr);
        printf("\tMask: %p\n", ifa->ifa_netmask);
        printf("\tDst: %p\n", ifa->ifa_dstaddr);
        printf("\tData: %p\n", ifa->ifa_data);
        
        family = ifa->ifa_addr->sa_family;
    }

    return 0;   
}

valgrind 打印出这个:

==18313== Memcheck, a memory error detector
==18313== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==18313== Using Valgrind-3.13.0 and LibVEX; rerun with -h for copyright info
==18313== Command: ./main.bin
==18313== IF: lo
        This: 0x49f8380
        Next: 0x49f8438
        Flags: 10049
        Addr: 0x49f83b800000000
        Mask: (nil)
        Dst: 0x49f840000000000
        Data: 0x49f89f800000000
==18313== Invalid read of size 2
==18313==    at 0x10899C: main (main.c:28)
==18313==  Address 0x49f83b800000000 is not stack'd, malloc'd or (recently) free'd
==18313==
==18313==
==18313== Process terminating with default action of signal 11 (SIGSEGV)
==18313==  Access not within mapped region at address 0x49F83B800000000
==18313==    at 0x10899C: main (main.c:28)
==18313==  If you believe this happened as a result of a stack
==18313==  overflow in your program's main thread (unlikely but
==18313==  possible), you can try to increase the size of the
==18313==  main thread stack using the --main-stacksize= flag.
==18313==  The main thread stack size used in this run was 8388608.
==18313==
==18313== HEAP SUMMARY:
==18313==     in use at exit: 1,944 bytes in 1 blocks
==18313==   total heap usage: 8 allocs, 7 frees, 7,476 bytes allocated
==18313==
==18313== LEAK SUMMARY:
==18313==    definitely lost: 0 bytes in 0 blocks
==18313==    indirectly lost: 0 bytes in 0 blocks
==18313==      possibly lost: 0 bytes in 0 blocks
==18313==    still reachable: 1,944 bytes in 1 blocks
==18313==         suppressed: 0 bytes in 0 blocks
==18313== Rerun with --leak-check=full to see details of leaked memory
==18313==
==18313== For counts of detected and suppressed errors, rerun with: -v
==18313== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0) Segmentation fault

您可能会看到 ifa_addr 的指针是 0x49f83b800000000，它被报告为“未堆栈、malloc 或(最近)释放”
有人遇到同样的问题吗？
谢谢

Answer 1

显然将 -fpack-struct=2 传递给 gcc 导致了这个问题