LIBSSH2和dso_dlfcn.c：...对"DLOPEN"的未定义引用

Question

我正在尝试使用静态libgit2、openssl和libssh2编译git2go。我的最终目标是能够编译go二进制文件，无需安装这些库即可进行部署。我在SO上发现了一个类似的问题，我用它来创建以下构建库的脚本

OPENSSL:

#!/bin/sh
set -ex
INSTALL_PATH="$PWD/install"
SUBMODULE_PATH="$PWD/submodules/openssl"
cd $SUBMODULE_PATH &&
mkdir -p $INSTALL_PATH/lib &&
mkdir -p build &&
# Switch to a stable version
git checkout OpenSSL_1_0_2-stable &&
./config threads no-shared --prefix=$INSTALL_PATH -fPIC -DOPENSSL_PIC &&
make depend &&
make &&
make install

LIBSSH2:

#!/bin/sh
set -ex
INSTALL_PATH="$PWD/install"
SUBMODULE_PATH="$PWD/submodules/libssh2"
# without this, the system's openssl shared object gets linked in
export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$INSTALL_PATH/lib/pkgconfig:$INSTALL_PATH/lib64/pkgconfig"
cd $SUBMODULE_PATH &&
mkdir -p $INSTALL_PATH/lib &&
mkdir build
cd build &&
cmake -DTHREADSAFE=ON 
      -DBUILD_CLAR=OFF 
      -DBUILD_SHARED_LIBS=OFF 
      -DCMAKE_C_FLAGS=-fPIC 
      -DCMAKE_BUILD_TYPE="RelWithDebInfo" 
      -DCMAKE_INSTALL_PREFIX=$INSTALL_PATH 
      .. &&
cmake --build .
make install

我正在将以下补丁应用于git2go分支next中构建libgit2的脚本，以确保PKG_CONFIG_PATH指向静态openssl和libssh2库

LIBGIT2:

--- build-libgit2-static.sh.orig    2016-04-14 22:49:53.000000000 -0700
+++ build-libgit2-static.sh 2016-04-14 22:52:04.000000000 -0700
@@ -2,10 +2,12 @@
 set -ex
-VENDORED_PATH=vendor/libgit2
+INSTALL_PATH="$PWD/install"
+VENDORED_PATH="$PWD/submodules/git2go/vendor/libgit2"
+export PKG_CONFIG_PATH="$PKG_CONFIG_PATH:$INSTALL_PATH/lib/pkgconfig:$INSTALL_PATH/lib64/pkgconfig"
 cd $VENDORED_PATH &&
-mkdir -p install/lib &&
+mkdir -p $INSTALL_PATH/lib &&
 mkdir -p build &&
 cd build &&
 cmake -DTHREADSAFE=ON 
@@ -13,7 +15,8 @@
       -DBUILD_SHARED_LIBS=OFF 
       -DCMAKE_C_FLAGS=-fPIC 
       -DCMAKE_BUILD_TYPE="RelWithDebInfo" 
-      -DCMAKE_INSTALL_PREFIX=../install 
+      -DCMAKE_INSTALL_PREFIX=$INSTALL_PATH 
       .. &&
 cmake --build .
+make install

这个设置最终创建了一个本地install目录，其中安装了所有库。我使用上面的脚本编译openssl。然后在编译libssh2时得到以下输出：

...
Found OpenSSL: (path to project)/install/lib/libssl.a;(path to project)/install/lib/libcrypto.a (found version "1.0.2h-dev")
...
Linking C static library libssh2.a
gmake[3]: Leaving directory `(path to project)/submodules/libssh2/build'
[ 46%] Built target libssh2
gmake[3]: Entering directory `(path to project)/submodules/libssh2/build'
Scanning dependencies of target example-direct_tcpip
gmake[3]: Leaving directory `(path to project)/submodules/libssh2/build'
gmake[3]: Entering directory `(path to project)/submodules/libssh2/build'
[ 48%] Building C object example/CMakeFiles/example-direct_tcpip.dir/direct_tcpip.c.o
Linking C executable example-direct_tcpip
(path to project)/install/lib/libcrypto.a(dso_dlfcn.o): In function `dlfcn_globallookup':
dso_dlfcn.c:(.text+0x11): undefined reference to `dlopen'
dso_dlfcn.c:(.text+0x24): undefined reference to `dlsym'
dso_dlfcn.c:(.text+0x2f): undefined reference to `dlclose'
(path to project)/install/lib/libcrypto.a(dso_dlfcn.o): In function `dlfcn_bind_func':
dso_dlfcn.c:(.text+0x354): undefined reference to `dlsym'
dso_dlfcn.c:(.text+0x412): undefined reference to `dlerror'
(path to project)/install/lib/libcrypto.a(dso_dlfcn.o): In function `dlfcn_bind_var':
dso_dlfcn.c:(.text+0x484): undefined reference to `dlsym'
dso_dlfcn.c:(.text+0x542): undefined reference to `dlerror'
(path to project)/install/lib/libcrypto.a(dso_dlfcn.o): In function `dlfcn_load':
dso_dlfcn.c:(.text+0x5a9): undefined reference to `dlopen'
dso_dlfcn.c:(.text+0x60d): undefined reference to `dlclose'
dso_dlfcn.c:(.text+0x645): undefined reference to `dlerror'
(path to project)/install/lib/libcrypto.a(dso_dlfcn.o): In function `dlfcn_pathbyaddr':
dso_dlfcn.c:(.text+0x6d1): undefined reference to `dladdr'
dso_dlfcn.c:(.text+0x731): undefined reference to `dlerror'
(path to project)/install/lib/libcrypto.a(dso_dlfcn.o): In function `dlfcn_unload':
dso_dlfcn.c:(.text+0x792): undefined reference to `dlclose'
collect2: error: ld returned 1 exit status
gmake[3]: Leaving directory `(path to project)/submodules/libssh2/build'
gmake[2]: Leaving directory `(path to project)/submodules/libssh2/build'
gmake[1]: Leaving directory `(path to project)(path to project)/submodules/libssh2/build'
gmake[3]: *** [example/example-direct_tcpip] Error 1
gmake[2]: *** [example/CMakeFiles/example-direct_tcpip.dir/all] Error 2
gmake[1]: *** [all] Error 2
make: *** [build-libssh2] Error 2

您可以看到正在使用静态openssl。显然，libdl没有链接到libcrypto。编译openssl时的输出具有EX_LIBS=-ldl。这应该包括图书馆吗？我已经尝试在openssl安装脚本中使用LDLIBS=-ldl，但仍然出现相同的错误。我几乎尝试过搜索词libcrypto undefined reference to 'dlopen'的所有SO答案，但都没有成功。任何帮助都将不胜感激

Answer 1

由于我不熟悉pig-config，我切换到Autoconf:

#!/bin/sh
set -ex
INSTALL_PATH="$PWD/install"
SUBMODULE_PATH="$PWD/submodules/libssh2"
mkdir -p $INSTALL_PATH/lib &&
cd $SUBMODULE_PATH &&
./buildconf
./configure --prefix=$INSTALL_PATH --libdir=$INSTALL_PATH/lib64 --with-openssl CFLAGS="-fPIC" LDFLAGS="-m64 -L$INSTALL_PATH/lib -L$INSTALL_PATH/lib64" LIBS=-ldl
make
make install

这已成功编译。

Answer 2

我发现将target_link_libraries(libssh2 ${CMAKE_DL_LIBS})添加到src/CMakeLists.txt（如本文所述）可以解决问题中提到的问题。请注意，我使用的是libssh2.8.0和最新的OpenSSL（5de683d），但我认为OpenSSL_1_02-stable也是如此。

因此，LIBSSH2的构建代码是：

# inside libssh2 root
printf 'ntarget_link_libraries(libssh2 ${CMAKE_DL_LIBS})' >> src/CMakeLists.txt
mkdir build && cd build
cmake -DTHREADSAFE=ON 
      -DBUILD_CLAR=OFF 
      -DBUILD_SHARED_LIBS=OFF 
      -DCMAKE_C_FLAGS=-fPIC 
      -DCMAKE_BUILD_TYPE="RelWithDebInfo" 
      -DCMAKE_INSTALL_PREFIX=$INSTALL_PATH 
      .. &&
cmake --build .
make install

注意：我还必须添加target_link_libraries(libssh2 pthread)，因为我在最新版本中得到了对pthread的未定义引用。