why is linking to libOpenCL.dylib failing with undefined symbol - c++

Question

I am trying to build the pocl library on MacOS
System:
MBP 16" 2019
Intel i9, AMD Radeon 5500m
Mac OS 12.4
using bash, instead of zsh
llvm from home-brew, -version 14
I have the following in my .bash_profile to setup the build environment
export PATH=/usr/local/opt/llvm/bin:$PATH
export CC=clang
export CMAKE_C_COMPILER=clang
export CXX=clang++
export CMAKE_CXX_COMPILER=clang++
I go and clone the repo with git, cd into the source directory, mkdir build
Then in build/ run:
cmake .. -DENABLE_TESTS=OFF -DENABLE_EXAMPLES=OFF -DENABLE_ICD=OFF
The config seems to work and then when I run make everything builds, and gets to the end but then gives me the following error:
[100%] Linking C executable poclcc
clang-14: warning: argument unused during compilation: '-pie' [-Wunused-command-line-argument]
Undefined symbols for architecture x86_64:
"_clBuildProgram", referenced from:
_main in poclcc.c.o
_poclu_load_program_multidev in libpoclu.a(misc.c.o)
"_clCreateCommandQueue", referenced from:
_poclu_get_any_device2 in libpoclu.a(misc.c.o)
_poclu_get_multiple_devices in libpoclu.a(misc.c.o)
"_clCreateContext", referenced from:
_main in poclcc.c.o
_poclu_get_any_device2 in libpoclu.a(misc.c.o)
_poclu_get_multiple_devices in libpoclu.a(misc.c.o)
"_clCreateContextFromType", referenced from:
_poclu_create_any_context in libpoclu.a(misc.c.o)
"_clCreateProgramWithBinary", referenced from:
_poclu_load_program_multidev in libpoclu.a(misc.c.o)
"_clCreateProgramWithIL", referenced from:
_poclu_load_program_multidev in libpoclu.a(misc.c.o)
"_clCreateProgramWithSource", referenced from:
_main in poclcc.c.o
_poclu_load_program_multidev in libpoclu.a(misc.c.o)
"_clGetDeviceIDs", referenced from:
_main in poclcc.c.o
_poclu_get_any_device2 in libpoclu.a(misc.c.o)
_poclu_get_multiple_devices in libpoclu.a(misc.c.o)
"_clGetDeviceInfo", referenced from:
_main in poclcc.c.o
_poclu_load_program_multidev in libpoclu.a(misc.c.o)
"_clGetPlatformIDs", referenced from:
_main in poclcc.c.o
_poclu_create_any_context in libpoclu.a(misc.c.o)
_poclu_get_any_device2 in libpoclu.a(misc.c.o)
_poclu_get_multiple_devices in libpoclu.a(misc.c.o)
"_clGetProgramBuildInfo", referenced from:
_main in poclcc.c.o
_poclu_show_program_build_log in libpoclu.a(misc.c.o)
"_clGetProgramInfo", referenced from:
_main in poclcc.c.o
_poclu_show_program_build_log in libpoclu.a(misc.c.o)
"_clReleaseContext", referenced from:
_main in poclcc.c.o
"_clReleaseProgram", referenced from:
_main in poclcc.c.o
ld: symbol(s) not found for architecture x86_64
I checked and libOpenCL.dylib was successfully built in the pocl/build/lib/CL/ directory. Just as a check, I tried compiling clinfo with a direct link to this library and it gave me the same set of error messages shown above.
Running nm libOpenCL.dylib | grep clBuildProgram prints the following:
0000000000013850 t _clBuildProgram
So its in there, but it is a local text section symbol. I don't actually know what that means though, and if that means it should work, or should not work. I don't actually understand what the problem is here or why this linking is failing, or what to do about it. Looking for some guidance on that.

Answer 1

The meaning of the lower case t is that the symbols are local, i.e. not externally visible to linking programs. Upper case T would be externally visible.
POCL has a number of configuration options, not all of which are documented in the Build section of the docs. The VISIBILITY_HIDDEN option is on by default unless the ENABLE_PROXY option is on.
In build/, running:
cmake .. -DENABLE_ICD=OFF -DVISIBILITY_HIDDEN=OFF
and then:
make
the compile succeeds to the end. Then in build/lib/CL/ running:
nm libOpenCL.dylib | grep clBuildProgram
now prints:
0000000000013790 T _clBuildProgram