redhat-rpm-config/brp-llvm-compile-lto-elf

#!/usr/bin/bash -eu

CLANG_FLAGS=$@

if [ -z "$RPM_BUILD_ROOT" ] || [ "$RPM_BUILD_ROOT" = "/" ]; then
	exit 0
fi

NCPUS=${RPM_BUILD_NCPUS:-1}
TMPDIR=`mktemp -d`

check_convert_bitcode () {
  local file_name=$(realpath ${1})
  local file_type=$(file ${file_name})

  if [[ "${file_type}" == *"LLVM IR bitcode"*  ]]; then
    # check for an indication that the bitcode was
    # compiled with -flto
    llvm-bcanalyzer -dump ${file_name} | grep -xP '.*\-flto((?!-fno-lto).)*' 2>&1 > /dev/null
    if [ $? -eq 0 ]; then
      echo "Compiling LLVM bitcode file ${file_name}."
      # create path to file in temp dir
      # move file to temp dir with llvm .bc extension for clang
      mkdir -p ${TMPDIR}/$(dirname ${file_name})
      mv $file_name ${TMPDIR}/${file_name}.bc
      clang -c ${CLANG_FLAGS} -fno-lto -Wno-unused-command-line-argument ${TMPDIR}/${file_name}.bc -o ${file_name}
    fi
  elif [[ "${file_type}" == *"current ar archive"*  ]]; then
    echo "Unpacking ar archive ${file_name} to check for LLVM bitcode components."
    # create archive stage for objects
    local archive_stage=$(mktemp -d)
    local archive=${file_name}
    pushd ${archive_stage}
    ar x ${archive}
    for archived_file in $(find -not -type d); do
      check_convert_bitcode ${archived_file}
      echo "Repacking ${archived_file} into ${archive}."
      ar r ${archive} ${archived_file}
    done
    popd
  fi
}

echo "Checking for LLVM bitcode artifacts"

export -f check_convert_bitcode
find "$RPM_BUILD_ROOT" -type f -name "*.[ao]" -print0 | \
  xargs -0 -n1 -P$NCPUS sh -c "check_convert_bitcode \$@" ARG0