How to generate position independent code in Halide with ahead of time compilation - halide

Question

I'm trying out halide and want to build a small shared library on top of it. But the code generated by Halide's AOT compilation seems not being position independent. How do I link the objects generated by Halide into my shared library?
[Update] extracted a small example from my code.
Specifically I used a generator with c++:
class SimpleAddition : public Halide::Generator<SimpleAddition> {
public:
SimpleAddition() : vars(4) {}
Input<Halide::Buffer<>> lhs{"lhs"};
Input<Halide::Buffer<>> rhs{"rhs"};
Output<Halide::Buffer<>> out{"out"};
std::vector<Var> vars;
void generate() {
out(vars) = lhs(vars) + rhs(vars);
}
};
HALIDE_REGISTER_GENERATOR(SimpleAddition, simple_addition)
with helpers from CMake:
halide_library(ops SRCS ${CMAKE_CURRENT_LIST_DIR}/src/simple_addition.cc
GENERATOR_NAME simple_addition
GENERATOR_ARGS lhs.type=float32 lhs.dim=4 rhs.type=float32 rhs.dim=4 out.type=float32)
and got the following error:
/usr/bin/ld: ./genfiles/halide_rt_host/halide_rt_host.a(halide_rt_host.a.o): relocation R_X86_64_PC32 against symbol `_ZN6Halide7Runtime8Internal13custom_mallocE' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status
I also tried generating object by running the generator myself (without CMake wrapper) with -e o,h, and similarly with llvm bitcode followed by llc -relocation-model=pic, also Func::compile_to_object. similar error occurred when I try to link the generated object back to shared library:
/usr/bin/ld: halide_runtime_x86.o: relocation R_X86_64_PC32 against symbol `_ZN6Halide7Runtime8Internal13custom_mallocE' can not be used when making a shared object; recompile with -fPIC
/usr/bin/ld: final link failed: bad value
collect2: error: ld returned 1 exit status
I'm running this on Ubuntu 18.10. Both Halide and my code are compiled with gcc-8.2.0. LLVM/Clang-7 is the one shipped in their repository. Halide is built with simple cmake ../ && make && make install.
For compiler flags of my testing code, command used in CMake is add_libarary(mylib SHARED ...). Non-CMake build is with flags like -fPIC -shared, nothing special since I'm still learning.

Answer 1

Halide should be generating PIC by default (see Codegen_Internal.cpp, make_target_machine()). What architecture are you targeting? What compiler/linker are you using, with what options, etc?