[flang-commits] [flang] [clang] [flang][Driver] Let the linker fail on multiple definitions of main() (PR #73124)

[Michael Klemm via flang-commits]

mjklemm wrote:

> Chipping into the discussion, since this patch I can also no longer build OpenBLAS or PETSc. OpenBLAS for example fails with
> 
> ```
> $ clang -v -O3 -mcpu=native  -DHAVE_C11 -Wall -DF_INTERFACE_GFORT -fPIC -DSMP_SERVER -DNO_WARMUP -DMAX_CPU_NUMBER=72 -DMAX_PARALLEL_NUMBER=1 -DMAX_STACK_ALLOC=2048 -DNO_AFFINITY -DVERSION="\"0.3.25\"" -DBUILD_SINGLE -DBUILD_DOUBLE -DBUILD_COMPLEX -DBUILD_COMPLEX16  utest/CMakeFiles/openblas_utest.dir/utest_main.c.o utest/CMakeFiles/openblas_utest.dir/test_min.c.o utest/CMakeFiles/openblas_utest.dir/test_amax.c.o utest/CMakeFiles/openblas_utest.dir/test_ismin.c.o utest/CMakeFiles/openblas_utest.dir/test_rotmg.c.o utest/CMakeFiles/openblas_utest.dir/test_rot.c.o utest/CMakeFiles/openblas_utest.dir/test_axpy.c.o utest/CMakeFiles/openblas_utest.dir/test_dsdot.c.o utest/CMakeFiles/openblas_utest.dir/test_dnrm2.c.o utest/CMakeFiles/openblas_utest.dir/test_swap.c.o utest/CMakeFiles/openblas_utest.dir/test_dotu.c.o utest/CMakeFiles/openblas_utest.dir/test_potrs.c.o utest/CMakeFiles/openblas_utest.dir/test_kernel_regress.c.o -o utest/openblas_utest  -Wl,-rpath,/.../openblas/build/lib  lib/libopenblas.so.0.3  -lm
> clang version 18.0.0 (git at github.com:llvm/llvm-project.git 17feb330aab39c6c0c21ee9b02efb484dfb2261e)
> Target: aarch64-unknown-linux-gnu
> Thread model: posix
> InstalledDir: /.../llvm/trunk/bin
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/11
> Found candidate GCC installation: /usr/lib/gcc/aarch64-linux-gnu/12
> Selected GCC installation: /usr/lib/gcc/aarch64-linux-gnu/12
> Candidate multilib: .;@m64
> Selected multilib: .;@m64
> Found CUDA installation: /usr/local/cuda, version 
>  "/usr/bin/ld" -EL -z relro --hash-style=gnu --eh-frame-hdr -m aarch64linux -pie -dynamic-linker /lib/ld-linux-aarch64.so.1 -o utest/openblas_utest /lib/aarch64-linux-gnu/Scrt1.o /lib/aarch64-linux-gnu/crti.o /usr/lib/gcc/aarch64-linux-gnu/12/crtbeginS.o -L/.../llvm/trunk/lib/clang/18/lib/aarch64-unknown-linux-gnu -L/usr/lib/gcc/aarch64-linux-gnu/12 -L/lib/aarch64-linux-gnu -L/usr/lib/aarch64-linux-gnu -L/lib -L/usr/lib -L/.../llvm/trunk/lib utest/CMakeFiles/openblas_utest.dir/utest_main.c.o utest/CMakeFiles/openblas_utest.dir/test_min.c.o utest/CMakeFiles/openblas_utest.dir/test_amax.c.o utest/CMakeFiles/openblas_utest.dir/test_ismin.c.o utest/CMakeFiles/openblas_utest.dir/test_rotmg.c.o utest/CMakeFiles/openblas_utest.dir/test_rot.c.o utest/CMakeFiles/openblas_utest.dir/test_axpy.c.o utest/CMakeFiles/openblas_utest.dir/test_dsdot.c.o utest/CMakeFiles/openblas_utest.dir/test_dnrm2.c.o utest/CMakeFiles/openblas_utest.dir/test_swap.c.o utest/CMakeFiles/openblas_utest.dir/test_dotu.c.o utest/CMakeFiles/openblas_utest.dir/test_potrs.c.o utest/CMakeFiles/openblas_utest.dir/test_kernel_regress.c.o -rpath /.../openblas/build/lib lib/libopenblas.so.0.3 -lm -lgcc --as-needed -lgcc_s --no-as-needed -lc -lgcc --as-needed -lgcc_s --no-as-needed /usr/lib/gcc/aarch64-linux-gnu/12/crtendS.o /lib/aarch64-linux-gnu/crtn.o
> /usr/bin/ld: lib/libopenblas.so.0.3: undefined reference to `_QQEnvironmentDefaults'
> /usr/bin/ld: lib/libopenblas.so.0.3: undefined reference to `_QQmain'
> ```

Thanks for the report!  Can you please tell me how OpenBLAS was built?  I'm trying to replicate this, but I do not see a reference to `_QQmain` or the likes in the OpenBLAS library that I build on x86.

https://github.com/llvm/llvm-project/pull/73124