unix: parameterize the name of the host compiler

Let's define the name of the host's C compiler in our YAML
config file and make it available as an environment variable in
builds. This makes the code in build scripts simpler, as it doesn't
have to sniff the triple or know much about the environment.

Author: indygreg

cpython-unix/build-cpython.sh

@@ -28,9 +28,6 @@ tar -xf pip-${PIP_VERSION}.tar.gz
 if [ "${BUILD_TRIPLE}" != "${TARGET_TRIPLE}" ]; then
   pushd "Python-${PYTHON_VERSION}"
 
-  OLD_CC=${CC}
-  unset CC
-
   # When cross-compiling, we need to build a host Python that has working zlib
   # and ctypes extensions, otherwise various things fail. (`make install` fails
   # without zlib and setuptools / pip used by target install fail due to missing
@@ -53,7 +50,7 @@ if [ "${BUILD_TRIPLE}" != "${TARGET_TRIPLE}" ]; then
       ;;
   esac
 
-  CFLAGS="${EXTRA_HOST_CFLAGS}" CPPFLAGS="${EXTRA_HOST_CFLAGS}" LDFLAGS="${EXTRA_HOST_LDFLAGS}" ./configure --prefix "${TOOLS_PATH}/pyhost"
+  CC="${HOST_CC}" CFLAGS="${EXTRA_HOST_CFLAGS}" CPPFLAGS="${EXTRA_HOST_CFLAGS}" LDFLAGS="${EXTRA_HOST_LDFLAGS}" ./configure --prefix "${TOOLS_PATH}/pyhost"
 
   # When building on macOS 10.15 (and possibly earlier) using the 11.0
   # SDK, the _ctypes extension fails to import due to a missing symbol on
@@ -73,8 +70,6 @@ if [ "${BUILD_TRIPLE}" != "${TARGET_TRIPLE}" ]; then
   # at the front of PATH.
   export PATH="${TOOLS_PATH}/pyhost/bin:${PATH}"
 
-  export CC="${OLD_CC}"
-
   popd
   # Nuke and re-pave the source directory out of paranoia.
   rm -rf "Python-${PYTHON_VERSION}"

cpython-unix/build-libX11.sh

@@ -75,39 +75,12 @@ if [ "${BUILD_TRIPLE}" != "${TARGET_TRIPLE}" ]; then
   esac
 fi
 
-case "${TARGET_TRIPLE}" in
-  aarch64-unknown-linux-gnu)
-    CC_FOR_BUILD=gcc
-    ;;
-  armv7-unknown-linux-gnueabi)
-    CC_FOR_BUILD=gcc
-    ;;
-  armv7-unknown-linux-gnueabihf)
-    CC_FOR_BUILD=gcc
-    ;;
-  mips-unknown-linux-gnu)
-    CC_FOR_BUILD=gcc
-    ;;
-  mipsel-unknown-linux-gnu)
-    CC_FOR_BUILD=gcc
-    ;;
-  mips64el-unknown-linux-gnuabi64)
-    CC_FOR_BUILD=gcc
-    ;;
-  s390x-unknown-linux-gnu)
-    CC_FOR_BUILD=gcc
-    ;;
-  *)
-    CC_FOR_BUILD=clang
-    ;;
-esac
-
 # CC_FOR_BUILD is here because configure doesn't look for `clang` when
 # cross-compiling. So we force it.
 CFLAGS="${EXTRA_TARGET_CFLAGS} -fPIC -I/tools/deps/include" \
   CPPFLAGS="${EXTRA_TARGET_CFLAGS} -fPIC -I/tools/deps/include" \
   LDFLAGS="${EXTRA_TARGET_LDFLAGS}" \
-  CC_FOR_BUILD="${CC_FOR_BUILD}" \
+  CC_FOR_BUILD="${HOST_CC}" \
   CFLAGS_FOR_BUILD="-I/tools/deps/include" \
   CPPFLAGS_FOR_BUILD="-I/tools/deps/include" \
   ./configure \

cpython-unix/build-ncurses.sh

@@ -19,20 +19,11 @@ tar -xf ncurses-${NCURSES_VERSION}.tar.gz
 if [[ "${BUILD_TRIPLE}" != "${TARGET_TRIPLE}" && "${PYBUILD_PLATFORM}" != "macos" ]]; then
   echo "building host ncurses to provide modern tic for cross-compile"
 
-  OLD_CC=${CC}
-  unset CC
-
-  if [ -e "${TOOLS_PATH}/${TOOLCHAIN}/bin/clang" ]; then
-    export CC="${TOOLS_PATH}/${TOOLCHAIN}/bin/clang"
-  fi
-
   pushd ncurses-${NCURSES_VERSION}
-  ./configure --prefix=${TOOLS_PATH}/host --without-cxx --without-tests --without-manpages --enable-widec
+  CC="${HOST_CC}" ./configure --prefix=${TOOLS_PATH}/host --without-cxx --without-tests --without-manpages --enable-widec
   make -j ${NUM_CPUS}
   make -j ${NUM_CPUS} install
 
-  export CC=${OLD_CC}
-
   popd
 
   # Nuke and re-pave the source directory.
@@ -61,13 +52,7 @@ CONFIGURE_FLAGS="
 # and this value not being equal, even though using the same binary with
 # different compiler flags is doable!
 if [[ "${BUILD_TRIPLE}" != "${TARGET_TRIPLE}" && "${PYBUILD_PLATFORM}" != "macos" ]]; then
-  # Look for and use our Clang toolchain by default. If not present, fall
-  # back to likely path to system GCC.
-  if [ -e "${TOOLS_PATH}/${TOOLCHAIN}/bin/clang" ]; then
-    CONFIGURE_FLAGS="${CONFIGURE_FLAGS} --with-build-cc=${TOOLS_PATH}/${TOOLCHAIN}/bin/clang"
-  else
-    CONFIGURE_FLAGS="${CONFIGURE_FLAGS} --with-build-cc=/usr/bin/x86_64-linux-gnu-gcc"
-  fi
+  CONFIGURE_FLAGS="${CONFIGURE_FLAGS} --with-build-cc=$(which "${HOST_CC}")"
 fi
 
 if [ "${PYBUILD_PLATFORM}" = "macos" ]; then

cpython-unix/build.py

@@ -89,6 +89,8 @@ def add_target_env(env, build_platform, target_triple, build_env):
 
     settings = get_target_settings(TARGETS_CONFIG, target_triple)
 
+    env["HOST_CC"] = settings["host_cc"]
+
     if settings.get("needs_toolchain"):
         if "musl" in target_triple:
             env["CC"] = "musl-clang"

cpython-unix/targets.yml

@@ -12,6 +12,10 @@
 # needs
 #    Packages required to build Python.
 #
+# host_cc
+#    Path to C compiler to use when producing binaries targeting the
+#    current build environment.
+#
 # openssl_target
 #    Name of OpenSSL platform build target.
 
@@ -20,6 +24,7 @@ aarch64-apple-darwin:
   host_platforms:
     - darwin
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bzip2
     - libedit
@@ -38,6 +43,7 @@ aarch64-apple-ios:
   host_platforms:
     - darwin
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bzip2
     - libffi
@@ -50,6 +56,7 @@ aarch64-unknown-linux-gnu:
   host_platforms:
     - linux
   docker_image_suffix: .cross
+  host_cc: /usr/bin/x86_64-linux-gnu-gcc
   needs:
     - bdb
     - binutils
@@ -76,6 +83,7 @@ arm64-apple-tvos:
   host_platforms:
     - darwin
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bzip2
     - sqlite
@@ -87,6 +95,7 @@ armv7-unknown-linux-gnueabi:
   host_platforms:
     - linux
   docker_image_suffix: .cross
+  host_cc: /usr/bin/x86_64-linux-gnu-gcc
   needs:
     - bdb
     - binutils
@@ -113,6 +122,7 @@ armv7-unknown-linux-gnueabihf:
   host_platforms:
     - linux
   docker_image_suffix: .cross
+  host_cc: /usr/bin/x86_64-linux-gnu-gcc
   needs:
     - bdb
     - binutils
@@ -139,6 +149,7 @@ i686-unknown-linux-gnu:
   host_platforms:
     - linux
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bdb
     - binutils
@@ -167,6 +178,7 @@ mips-unknown-linux-gnu:
   host_platforms:
     - linux
   docker_image_suffix: .cross
+  host_cc: /usr/bin/x86_64-linux-gnu-gcc
   needs:
     - bdb
     - binutils
@@ -193,6 +205,7 @@ mipsel-unknown-linux-gnu:
   host_platforms:
     - linux
   docker_image_suffix: .cross
+  host_cc: /usr/bin/x86_64-linux-gnu-gcc
   needs:
     - bdb
     - binutils
@@ -219,6 +232,7 @@ s390x-unknown-linux-gnu:
   host_platforms:
     - linux
   docker_image_suffix: .cross
+  host_cc: /usr/bin/x86_64-linux-gnu-gcc
   needs:
     - bdb
     - binutils
@@ -245,6 +259,7 @@ thumb7k-apple-watchos:
   host_platforms:
     - darwin
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bzip2
     - sqlite
@@ -255,6 +270,7 @@ thumb7k-apple-watchos:
 x86_64-apple-darwin:
   host_platforms:
     - darwin
+  host_cc: clang
   needs:
     - bzip2
     - libedit
@@ -273,6 +289,7 @@ x86_64-apple-ios:
   host_platforms:
     - darwin
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bzip2
     - libffi
@@ -285,6 +302,7 @@ x86_64-apple-tvos:
   host_platforms:
     - darwin
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bzip2
     - sqlite
@@ -295,6 +313,7 @@ x86_64-apple-watchos:
   host_platforms:
     - darwin
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bzip2
     - sqlite
@@ -306,6 +325,7 @@ x86_64-unknown-linux-gnu:
   host_platforms:
     - linux
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bdb
     - binutils
@@ -333,6 +353,7 @@ x86_64-unknown-linux-musl:
   host_platforms:
     - linux
   needs_toolchain: true
+  host_cc: clang
   needs:
     - bdb
     - binutils