How to force Bazel to use gcc? - c++

Question

Ubuntu 17.10
GCC Version: 5.4
Bazel Version: 0.9.0
TensorFlow: r1.5
CUDA 8.0 / cuDNN 6 / GTX 1080 Ti
How do I make Bazel use gcc for building TensorFlow from source?
While building, its running into compiler errors like:
error: 'errno' was not declared in this scope
while (nanosleep(&ts, &ts) != 0 && errno == EINTR) {}
Setting --verbose_failures flag, it shows that its not using /usr/bin/gcc-5 or /usr/bin/gcc for compiling
external/local_config_cuda/crosstool/clang/bin/crosstool_wrapper_driver_is_not_gcc -U_FORTIFY_SOURCE '-D_FORTIFY_SOURCE=1' -fstack-protector -fPIE -Wall -Wunused-but-set-parameter -Wno-free-nonheap-object -fno-omit-frame-pointer -g0 -O2 -DNDEBUG -ffunction-sections -fdata-sections -g0 -DGEMMLOWP_ALLOW_SLOW_SCALAR_FALLBACK '-march=native' '-std=c++11' -g0 -MD -MF
Searching online, I found that the path to gcc and CC, CXX variables must be set in tools/cpp/CROSSTOOL. But where exactly is tools/cpp/CROSSTOOL?? How do I force bazel to use gcc-5?

Answer 1

I know next to nothing about cuda and tensorflow, but tensorflow doesn't use the same C++ toolchain that bazel autoconfigures when compiling with cuda, so the CC env variable trick won't work. The file crosstool_wrapper_driver_is_not_gcc is just a shell wrapper that could in theory still call your gcc (or it will be cuda). I'd run bazel with --subcommands to see the complete invocation of the failing action, then reproduce without bazel, and then go from there.