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使用gcc -lnetsnmp进行链接时出现未定义引用问题

linuxgccopensslraspberry-pisnmp
3
我正在尝试在树莓派上编译和运行需要snmp库的代码。然而，我遇到了链接错误，例如“未定义的引用'EVP_DigestUpdate'”。
过去几天里，我一直在研究这个问题，并发现通常情况下是因为snmp找不到ssl库crypto，例如如果您在链接对象时没有在-lsnmp之前指定-lcrypto，或者链接器无法找到-lcrypto。
然而，在我的树莓派上，我已经将所有必需的库安装在/usr/lib/gcc/arm-linux-gnueabihf中。
以下是我安装库的方式：
apt-get install libssl-dev libsnmp-dev libsnmp-base libsnmp30

我使用以下命令生成trap.o文件：
gcc -c -g -pedantic -Wall -Wshadow -I/home/pi/tests/h -I/usr/include trap.c -o trap.o

我使用以下命令将trap.o链接到库中：

gcc -static -g -pedantic -Wall -Wshadow trap.o -o trap -L/usr/lib/arm-linux-gnueabihf/lib -lcrypto -lpthread -lnetsnmpagent -lnetsnmpmibs -lnetsnmphelpers -lnetsnmp

然后我遇到了这个错误：
    gcc -static -g -pedantic -Wall -Wshadow trap.o -o trap -L/usr/lib/arm-linux-gnueabihf/lib -lcrypto -lpthread -lnetsnmpagent -lnetsnmpmibs -lnetsnmphelpers -lnetsnmp
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(system.o): In function `netsnmp_str_to_gid':
(.text+0x1144): warning: Using 'getgrnam' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(system.o): In function `netsnmp_str_to_gid':
(.text+0x1154): warning: Using 'endgrent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(system.o): In function `netsnmp_str_to_uid':
(.text+0x10d8): warning: Using 'getpwnam' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(system.o): In function `netsnmp_str_to_uid':
(.text+0x10e8): warning: Using 'endpwent' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(system.o): In function `netsnmp_getaddrinfo':
(.text+0x4a4): warning: Using 'getaddrinfo' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(system.o): In function `netsnmp_gethostbyaddr':
(.text+0x9f8): warning: Using 'gethostbyaddr' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
trap.o: In function `parse_address':
/home/pi/tests/trap.c:56: warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/crt1.o: In function `_start':
/build/glibc-6f8a9a/glibc-2.19/csu/../ports/sysdeps/arm/start.S:119: undefined reference to `main'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_random':
(.text+0x168): undefined reference to `RAND_bytes'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_generate_keyed_hash':
(.text+0x290): undefined reference to `EVP_md5'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_generate_keyed_hash':
(.text+0x2b4): undefined reference to `HMAC'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_generate_keyed_hash':
(.text+0x33c): undefined reference to `EVP_sha1'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_hash':
(.text+0x424): undefined reference to `EVP_sha1'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_hash':
(.text+0x42c): undefined reference to `EVP_MD_CTX_create'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_hash':
(.text+0x438): undefined reference to `EVP_DigestInit'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_hash':
(.text+0x448): undefined reference to `EVP_DigestUpdate'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_hash':
(.text+0x458): undefined reference to `EVP_DigestFinal'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_hash':
(.text+0x468): undefined reference to `EVP_MD_CTX_destroy'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_hash':
(.text+0x488): undefined reference to `EVP_md5'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_encrypt':
(.text+0x86c): undefined reference to `DES_key_sched'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_encrypt':
(.text+0x8a0): undefined reference to `DES_ncbc_encrypt'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_encrypt':
(.text+0x8c4): undefined reference to `DES_ncbc_encrypt'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_encrypt':
(.text+0x90c): undefined reference to `AES_set_encrypt_key'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_encrypt':
(.text+0x948): undefined reference to `AES_cfb128_encrypt'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_encrypt':
(.text+0xa74): undefined reference to `DES_key_sched'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_encrypt':
(.text+0xaac): undefined reference to `DES_ncbc_encrypt'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_decrypt':
(.text+0xc78): undefined reference to `AES_set_encrypt_key'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_decrypt':
(.text+0xcb0): undefined reference to `AES_cfb128_encrypt'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_decrypt':
(.text+0xd9c): undefined reference to `DES_key_sched'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(scapi.o): In function `sc_decrypt':
(.text+0xdd0): undefined reference to `DES_cbc_encrypt'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0x74): undefined reference to `EVP_MD_CTX_create'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0x98): undefined reference to `EVP_md5'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0xa4): undefined reference to `EVP_DigestInit'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0xe8): undefined reference to `EVP_DigestUpdate'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0x10c): undefined reference to `EVP_DigestFinal'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0x138): undefined reference to `EVP_MD_CTX_destroy'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0x178): undefined reference to `EVP_sha1'
/usr/lib/gcc/arm-linux-gnueabihf/4.9/../../../arm-linux-gnueabihf/libnetsnmp.a(keytools.o): In function `generate_Ku':
(.text+0x184): undefined reference to `EVP_DigestInit'
collect2: error: ld returned 1 exit status

问题可能是由于我安装的snmp库使用的openssl版本与我的环境中的不同造成的吗？我的libssl-dev和libsnmp-dev版本如下：

dpkg -l | grep libssl-dev：

ii  libssl-dev:armhf                      1.0.1k-3+deb8u5                           armhf        Secure Sockets Layer toolkit - development files

dpkg -l | grep libsnmp-dev:

ii  libsnmp-dev                           5.7.2.1+dfsg-1                            armhf        SNMP (Simple Network Management Protocol) development files

任何帮助都会受到赞赏，
谢谢。
1个回答
3
你所有未定义的引用都在libnetsnmp中，它们都是对libcrypto中定义的函数的未定义引用。这是因为在链接时-lcrypto在-lnetsnmp之前。
在链接序列中，需要符号定义的文件必须出现在提供定义的文件之前，因为链接器默认只会搜索库以查找先前在其他文件中被引用但未定义的符号的定义。 （您似乎已经误学了这个规则，方向相反）。来自man ld：

链接器仅会在命令行指定的位置一次性搜索存档文件。如果存档文件定义了某个在先前出现在命令行上的对象中未定义的符号，则链接器将包含存档文件中的相应文件。但是，在命令行后面出现的对象中的未定义符号不会导致链接器再次搜索存档文件。

因此，请在-lnetsnmp之后链接-lcrypto。
你说得对！我也必须在-lcrypto后面链接-ldl才能让它正常工作。现在我只收到一些警告，例如：“在静态链接的应用程序中使用'dlopen'需要在运行时从用于链接的glibc版本获取共享库”。这是否值得关注？ - mstaro
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