Error when linking executable

Code
1

Hi, guys. I am new to cmake currently and I am rewriting the building file of my project from Makefile to cmake.

When linking the executable, cmake says there has “undefined reference”, but I am sure I have added the correct libraries. So I display the debug info, and found that the only difference between my original Makefile command and cmake-generated command is the position of the linking flags. (The flags in the original command are after the output file while the flags in cmake command are before the output file.)

After I manually change the position of the flags, there have no such errors. So I want to figure out why the position of flags influences the linking process and how to solve it from my cmake file.

Here’s the probably helpful info. Can someone help? Thanks a lot ~

cmake-generated error command

/usr/bin/c++ -m64 -O2 -Wl,--no-undefined -nostdlib -nodefaultlibs -nostartfiles -L/opt/alibaba/teesdk/intel/sgxsdk/lib64 -Wl,--whole-archive -lsgx_trts -Wl,--no-whole-archive -Wl,--start-group -lsgx_tstdc -lsgx_tcrypto -lsgx_tservice -Wl,--end-group -Wl,-Bstatic -Wl,-Bsymbolic -Wl,--no-undefined -Wl,-pie,-eenclave_entry -Wl,--export-dynamic -Wl,--defsym,__ImageBase=0 -Wl,--gc-sections -Wl,-z,relro,-z,now,-z,noexecstack -Wl,--version-script=/root/QuoteGenerationSample/Enclave/Enclave.lds CMakeFiles/enclave.so.dir/Enclave.cpp.o CMakeFiles/enclave.so.dir/Enclave_t.c.o -o enclave.so

error info

/usr/bin/ld: CMakeFiles/enclave.so.dir/Enclave_t.c.o: in function `sgx_enclave_create_report':
Enclave_t.c:(.text.sgx_enclave_create_report+0x3f): undefined reference to `memcpy_s'
/usr/bin/ld: Enclave_t.c:(.text.sgx_enclave_create_report+0xb7): undefined reference to `memcpy_s'
/usr/bin/ld: Enclave_t.c:(.text.sgx_enclave_create_report+0x109): undefined reference to `memcpy_verw_s'
/usr/bin/ld: Enclave_t.c:(.text.sgx_enclave_create_report+0x126): undefined reference to `memcpy_verw_s'
/usr/bin/ld: Enclave_t.c:(.text.sgx_enclave_create_report+0x1f1): undefined reference to `memcpy_verw_s'
/usr/bin/ld: Enclave_t.c:(.text.sgx_enclave_create_report+0x217): undefined reference to `memcpy_verw_s'
/usr/bin/ld: Enclave_t.c:(.text.sgx_enclave_create_report+0x263): undefined reference to `memcpy_verw_s'
/usr/bin/ld: CMakeFiles/enclave.so.dir/Enclave_t.c.o:Enclave_t.c:(.text.sgx_enclave_c

manually fixed command

/usr/bin/c++ CMakeFiles/enclave.so.dir/Enclave_t.c.o CMakeFiles/enclave.so.dir/Enclave.cpp.o -o enclave.so -m64 -O2 -Wl,--no-undefined -nostdlib -nodefaultlibs -nostartfiles -L/opt/alibaba/teesdk/intel/sgxsdk/lib64 -Wl,--whole-archive -lsgx_trts -Wl,--no-whole-archive -Wl,--start-group -lsgx_tstdc -lsgx_tcrypto -lsgx_tservice -Wl,--end-group -Wl,-Bstatic -Wl,-Bsymbolic -Wl,--no-undefined -Wl,-pie,-eenclave_entry -Wl,--export-dynamic -Wl,--defsym,__ImageBase=0 -Wl,--gc-sections -Wl,-z,relro,-z,now,-z,noexecstack -Wl,--version-script=/root/QuoteGenerationSample/Enclave/Enclave.lds
2

I have the same “undefined reference” issue. However, the CMake generated command is in the latter form you provided. Therefore I believe it is not the order of flags that matters.

In my case, if I create and use a function (e.g., custom printf), which has the same definition to standard libraries, it will trigger this error.
Somehow, the reference goes to standard libraries rather than the embeded version provided by SGX SDK.
As a result, the linker cannot find the referred function with -nostdlib flag.

A confusing fact is that the editor can recognize the header files of these embeded libraries in SGX SDK.

If I modify my custom function to other names to avoid confusion with standard library, the problem is avoidedand the reference goes to the correct function.
However, this approach means that the embeded C/C++ libraries in SGX SDK cannot be used, which is very inconvenient.