c++ - 如何解决支持库中发生的段错误问题？

Question

我遇到了一个非常奇怪的问题。我可以通过以下小示例代码重现该问题:

#include <openssl/ssl.h>
#include <openssl/err.h>

#include <iostream>

void printSSLErrors()
{
    int l_err = ERR_get_error();
    while(l_err!=0)
    {
      std::cout << "SSL ERROR: " << ERR_error_string(l_err, NULL) << std::endl;
      l_err = ERR_get_error();
    }
}

int main(int argc, char* argv[]) {

    SSL_library_init();
    SSL_load_error_strings();

    // context
    SSL_CTX* mp_ctx;

    if(!(mp_ctx = SSL_CTX_new(SSLv23_server_method())))
    {
      printSSLErrors();
      return 0;
    }

    std::cout << "CTX created OK" << std::endl;

    // set certificate and private key
    if(SSL_CTX_use_certificate_file(mp_ctx, argv[1], SSL_FILETYPE_PEM)!=1)
    {
      printSSLErrors();
      return 0;
    }

    std::cout << "Certificate intialised OK" << std::endl;

    if(SSL_CTX_use_PrivateKey_file(mp_ctx, argv[2], SSL_FILETYPE_PEM)!=1)
    {
      printSSLErrors();
      return 0;
    }

    std::cout << "Key intialised OK" << std::endl;

    SSL_CTX_free(mp_ctx);
    ERR_free_strings();
}

当我编译它并使用 -lssl 链接它时，该程序按预期工作。然而，问题是 openssl 例程是应用程序的一部分，该应用程序也链接到 mysqlclient 库中。我现在用 -lssl -lmysqlclient 重新编译上面的代码(请注意，我没有在此处包含或使用该库中的任何内容)。如果我再次执行该程序，我会在打开的 ssl 库中遇到段错误。我最多可以从 gdb 中提取出来:

[Thread debugging using libthread_db enabled]
[New Thread -1208158528 (LWP 32359)]
CTX created OK
Certificate intialised OK

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread -1208158528 (LWP 32359)]
0x001b1213 in X509_get_pubkey () from /lib/libcrypto.so.4

(gdb) backtrace
#0  0x001b1213 in X509_get_pubkey () from /lib/libcrypto.so.4
#1  0x00de8a6c in SSL_rstate_string () from /lib/libssl.so.4
#2  0x086f2258 in ?? ()
#3  0xbffceb64 in ?? ()
#4  0x086f1130 in ?? ()
#5  0xbffceaa8 in ?? ()
#6  0x086f2258 in ?? ()
#7  0x086f0d90 in ?? ()
#8  0x00df4858 in ?? () from /lib/libssl.so.4
#9  0x086f2258 in ?? ()
#10 0x086f1130 in ?? ()
#11 0xbffceaa8 in ?? ()
#12 0x00de9d50 in SSL_CTX_use_PrivateKey_file () from /lib/libssl.so.4
Previous frame inner to this frame (corrupt stack?)
(gdb) frame 0
#0  0x001b1213 in X509_get_pubkey () from /lib/libcrypto.so.4

出于某种原因，这仅在我使用 mysqlclient v 15 而不是 mysqlclient v 16 时发生。这可能对任何人来说都太晦涩难解，但是一些关于如何链接代码本身甚至没有的动态库的评论use can cause these errors 会很有帮助。

系统是:

RHEL ES4、gcc 3.4.6、openssl-0.9.7a、MySQL-5.11

有什么想法吗？

编辑:这里是可能澄清一些事情的输出:

[Lieuwe ~]$ c++ openssl_test.cpp -lssl -o ssltest 
[Lieuwe ~]$ ./ssltest /etc/httpd/conf/certs/test.crt /etc/httpd/conf/certs/test.key 
CTX created OK
Certificate intialised OK
Key intialised OK
[Lieuwe ~]$ c++ openssl_test.cpp -lmysqlclient -lssl -o ssltest 
[Lieuwe ~]$ ./ssltest /etc/httpd/conf/certs/test.crt /etc/httpd/conf/certs/test.key 
CTX created OK
Certificate intialised OK
Segmentation fault (core dumped)
[Lieuwe ~]$ 

请注意，为此我使用了 apache 服务器也使用(和工作)的 crt 和 key 文件

编辑 2:这是程序的 valgrind 的(相关？)输出

CTX created OK
--5429-- REDIR: 0x5F6C80 (memchr) redirected to 0x4006184 (memchr)
Certificate intialised OK
==5429== Invalid read of size 4
==5429==    at 0xCF4205: X509_get_pubkey (in /lib/libcrypto.so.0.9.7a)
==5429==    by 0xDE8A6B: (within /lib/libssl.so.0.9.7a)
==5429==    by 0xDE9D4F: SSL_CTX_use_PrivateKey_file (in /lib/libssl.so.0.9.7a)
==5429==    by 0x8048C77: main (in /home/liwu/ssltest)
==5429==  Address 0x4219940 is 0 bytes inside a block of size 84 free'd
==5429==    at 0x4004EFA: free (vg_replace_malloc.c:235)
==5429==    by 0xC7FD00: CRYPTO_free (in /lib/libcrypto.so.0.9.7a)
==5429==    by 0xCE53A7: (within /lib/libcrypto.so.0.9.7a)
==5429==    by 0xCE5562: ASN1_item_free (in /lib/libcrypto.so.0.9.7a)
==5429==    by 0xCE0560: X509_free (in /lib/libcrypto.so.0.9.7a)
==5429==    by 0xDE979E: SSL_CTX_use_certificate_file (in /lib/libssl.so.0.9.7a)
==5429==    by 0x8048C23: main (in /home/liwu/ssltest)
==5429== 
==5429== Invalid read of size 4
==5429==    at 0xCD4A5F: EVP_PKEY_copy_parameters (in /lib/libcrypto.so.0.9.7a)
==5429==    by 0xDE8A7C: (within /lib/libssl.so.0.9.7a)
==5429==    by 0xDE9D4F: SSL_CTX_use_PrivateKey_file (in /lib/libssl.so.0.9.7a)
==5429==    by 0x8048C77: main (in /home/liwu/ssltest)
==5429==  Address 0x0 is not stack'd, malloc'd or (recently) free'd
==5429== 
==5429== Process terminating with default action of signal 11 (SIGSEGV)
==5429==  Access not within mapped region at address 0x0
==5429==    at 0xCD4A5F: EVP_PKEY_copy_parameters (in /lib/libcrypto.so.0.9.7a)
==5429==    by 0xDE8A7C: (within /lib/libssl.so.0.9.7a)
==5429==    by 0xDE9D4F: SSL_CTX_use_PrivateKey_file (in /lib/libssl.so.0.9.7a)
==5429==    by 0x8048C77: main (in /home/liwu/ssltest)
==5429== 

Answer 1

我建议在 Valgrind 下运行您的程序. Valgrind 旨在为此类问题提供帮助，并且通常比调试器更易于使用。

如果让我冒险猜测，我会首先怀疑您的应用程序中存在内存错误(或者，不太可能，在一个共享库中)，它对生成的可执行文件的内存布局很敏感。添加新的共享库或启用调试选项很可能会导致问题无缘无故地出现或消失。