Building Enzyme CMake - Undefined symbol: main about enzyme

[wsmoses]

Hm that looks like the linker didn't find your main function for some reason. Mind sharing the whole code which fails?

[jpmedinagl]

We were originally building the test files outside of the Enzyme library. However we're currently trying inside the Enzyme/enzyme/test/test_find_package folder. Trying to build the enzyme_test_2 executable (we removed the enzyme_test_1 executable due to errors with Clang). We just want to test (and compile) the main.c source file to see if __enzyme_autodiff works.

In that folder, we tried building the executable with

cmake -DEnzyme_DIR=/u/jpmedina/Enzyme/enzyme/build .

This was successful

But then when we type make
we get the same error again

[ 50%] Building C object CMakeFiles/enzyme_test_2.dir/main.c.o
[100%] Linking C executable enzyme_test_2
ld.lld: error: undefined symbol: main
>>> referenced by /usr/lib/gcc/x86_64-linux-gnu/9/../../../x86_64-linux-gnu/Scrt1.o:(_start)
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/enzyme_test_2.dir/build.make:97: enzyme_test_2] Error 1
make[1]: *** [CMakeFiles/Makefile2:83: CMakeFiles/enzyme_test_2.dir/all] Error 2
make: *** [Makefile:91: all] Error 2

For reference:
The code in /Enzyme/enzyme/test/test_find_package/CMakeLists.txt

cmake_minimum_required(VERSION 3.16)

project(enzyme_consumer LANGUAGES C)

find_package(Enzyme REQUIRED CONFIG NO_DEFAULT_PATH)
message("found dir ${Enzyme_DIR}")
message("found ${Enzyme_FOUND}")
get_property(importTargetsAfter DIRECTORY "${CMAKE_SOURCE_DIR}" PROPERTY IMPORTED_TARGETS)
message("imported targets ${importTargetsAfter}")

#add_subdirectory(${Enzyme_DIR} ${PROJECT_SOURCE_DIR}/build/enzyme)

#add_executable(enzyme_test_1 main.c)
#target_link_libraries(enzyme_test_1 PUBLIC ClangEnzymeFlags)

add_executable(enzyme_test_2 main.c)
target_compile_definitions(enzyme_test_2 PUBLIC -DNOVERSION)
target_link_libraries(enzyme_test_2 PUBLIC LLDEnzymeFlags)

The code for /Enzyme/enzyme/test/test_find_package/main.c

int printf(const char*, ...);

extern double __enzyme_autodiff(void*, double);

double square(double x) {
  return x * x;
}

double dsquare(double x) {
  return __enzyme_autodiff((void*) square, x);
}

int main() {
  for(double i=1; i<5; i++) {
    printf("%f %f\n", square(i), dsquare(i));
  }
#ifndef NOVERSION
  printf("Enzyme version %d %d %d\n", ENZYME_VERSION_MAJOR, ENZYME_VERSION_MINOR, ENZYME_VERSION_PATCH);
#endif
}

[jpmedinagl]

@wsmoses

We realized that we were unintentionally using gcc instead of clang.

Would it be possible to recognize this and throw and error to the user?