Linux CMake build dynamic library without linking depedencies - linux

Question

I'm coding a C++ library on Linux, the lib name is libic. libic use openssl. When I build libic on host Ubuntu 18.04, no error occurs. But when I cross-compile libic for arm, linker error when building libic shared target. The error is like below:
....
[100%] Linking CXX shared library libic.so
uclient.c:(.text+0xd96): undefined reference to `event_del'
uclient.c:(.text+0xd9e): undefined reference to `event_free'
uclient.c:(.text+0xdae): undefined reference to `event_del'
uclient.c:(.text+0xdb6): undefined reference to `event_free'
uclient.c:(.text+0xdf8): undefined reference to `SSL_get_shutdown'
uclient.c:(.text+0xe0a): undefined reference to `SSL_free'
uclient.c:(.text+0xe5c): undefined reference to `SSL_free'
uclient.c:(.text+0xe90): undefined reference to `event_base_free'
uclient.c:(.text+0xe98): undefined reference to `pthread_cancel'
uclient.c:(.text+0xed6): undefined reference to `SSL_get_shutdown'
uclient.c:(.text+0xefa): undefined reference to `SSL_set_shutdown'
uclient.c:(.text+0xf06): undefined reference to `SSL_shutdown'
uclient.c:(.text+0xf12): undefined reference to `SSL_set_shutdown'
uclient.c:(.text+0xf1a): undefined reference to `SSL_shutdown'
The configure log is below
-- Found PkgConfig: /usr/bin/pkg-config (found version "0.29.1")
-- Looking for pthread.h
-- Looking for pthread.h - found
-- Looking for pthread_create
-- Looking for pthread_create - not found
-- Check if compiler accepts -pthread
-- Check if compiler accepts -pthread - yes
-- Found Threads: TRUE
-- Found OpenSSL: /home/drone/tizen-studio/platforms/tizen-3.0/mobile/rootstraps/mobile-3.0-device.core/usr/lib/libcrypto.so (found version "1.0.2k")
-- Using OpenSSL 1.0.2k
-- Found CURL: /home/drone/tizen-studio/platforms/tizen-3.0/mobile/rootstraps/mobile-3.0-device.core/usr/lib/libcurl.so (found version "7.50.2")
--
-- C/C++:
-- C++ Compiler: /home/drone/Downloads/gcc-linaro-7.3.1-2018.05-x86_64_arm-linux-gnueabi/bin/arm-linux-gnueabi-g++ (ver 7.3.1)
-- C++ flags (Release): -mthumb -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi -std=c++1y -fPIC -O3 -DNDEBUG
-- C++ flags (Debug): -mthumb -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi -std=c++1y -fPIC -g
-- C Compiler: /home/drone/Downloads/gcc-linaro-7.3.1-2018.05-x86_64_arm-linux-gnueabi/bin/arm-linux-gnueabi-gcc
-- C flags (Release): -mthumb -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi -fPIC -O3 -DNDEBUG
-- C flags (Debug): -mthumb -fdata-sections -Wa,--noexecstack -fsigned-char -Wno-psabi -fPIC -g
-- CMAKE_INSTALL_PREFIX: /home/drake/Documents/code/libscs/packages/libscs
-- Linker flags (Release): -Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now
-- Linker flags (Debug): -Wl,--fix-cortex-a8 -Wl,--no-undefined -Wl,--gc-sections -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now
It seems with cross compile, libic requires to link with openssl. I want to ask that how can I build libic shared without linking with openssl?
Thanks for your support.

Answer 1

If your library depends on libssl, you cannot compile it without linking to libssl. Did you try getting the libssl package for the arm architecture? Off the top of my head, something around the lines of
dpkg --add-architecture arm
apt update
apt install libssl-dev:arm
Or maybe
dpkg --add-architecture arm64
apt update
apt install libssl-dev:arm64
Hope this helps!

Answer 2

Thank you guys, I've found the answer, the linker issue occurs because of this linker flag -Wl,--no-undefined. Just remove this linker option is OK