cc: add CLang support with INPUT_CLANG=1

It will compile the kernel and dependences with CLang.

Build and CCache dir will be separated.

run-tests-clang.sh and run-tests-dev-clang.sh set the env var.

Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>

Author: matttbe

README.md

@@ -89,6 +89,10 @@ If you didn't change the kernel code, it can be useful to skip the compilation
 part. You can then set `INPUT_BUILD_SKIP=1` to save a few seconds to start the
 VM.
 
+#### Use CLang instead of GCC
+
+Simply set `INPUT_CLANG=1` env var with all the commands you use.
+
 #### Not blocking with questions
 
 You can set `INPUT_NO_BLOCK=1` env var not to block if these files are present.
@@ -227,5 +231,5 @@ case, it will be required to clean the build dir in `.virtme/build`, e.g.
 ```bash
 docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --rm -it \
   mptcp/mptcp-upstream-virtme-docker:latest \
-  cmd rm -r .virtme/build/tools
+  cmd rm -r .virtme/build*/tools
 ```

entrypoint.sh

@@ -35,6 +35,10 @@ set_trace_off() {
 	fi
 }
 
+with_clang() {
+	[ "${INPUT_CLANG}" = "1" ]
+}
+
 set_trace_on
 
 # The behaviour can be changed with 'input' env var
@@ -83,6 +87,7 @@ BASH_PROFILE="/root/.bash_profile"
 
 VIRTME_WORKDIR="${KERNEL_SRC}/.virtme"
 VIRTME_BUILD_DIR="${VIRTME_WORKDIR}/build"
+with_clang && VIRTME_BUILD_DIR+="-clang"
 VIRTME_SCRIPTS_DIR="${VIRTME_WORKDIR}/scripts"
 VIRTME_PERF_DIR="${VIRTME_BUILD_DIR}/tools/perf"
 VIRTME_TOOLS_SBIN_DIR="${VIRTME_BUILD_DIR}/tools/sbin"
@@ -102,6 +107,7 @@ BPFTESTS_CONFIG="${BPFTESTS_DIR}/config"
 
 export CCACHE_MAXSIZE="${INPUT_CCACHE_MAXSIZE}"
 export CCACHE_DIR="${VIRTME_WORKDIR}/ccache"
+with_clang && CCACHE_DIR+="-clang"
 
 export KBUILD_OUTPUT="${VIRTME_BUILD_DIR}"
 export KCONFIG_CONFIG="${VIRTME_KCONFIG}"
@@ -300,6 +306,7 @@ check_source_exec_all() {
 }
 
 read -ra MAKE_ARGS <<< "${INPUT_MAKE_ARGS}"
+with_clang && MAKE_ARGS+=(LLVM=1 LLVM_IAS=1 CC=clang ARCH="${VIRTME_ARCH}")
 MAKE_ARGS_O=("${MAKE_ARGS[@]}" O="${VIRTME_BUILD_DIR}")
 
 _make_j() {
@@ -355,7 +362,13 @@ gen_kconfig() { local mode kconfig=() vck rc=0
 	kconfig+=(-e PANIC_ON_OOPS)
 
 	# Debug info for developers
-	kconfig+=(-e DEBUG_INFO -e DEBUG_INFO_DWARF4 -e GDB_SCRIPTS)
+	kconfig+=(-e DEBUG_INFO -e DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT -e GDB_SCRIPTS)
+	if with_clang; then
+		kconfig+=(-e DEBUG_INFO_DWARF_TOOLCHAIN_DEFAULT)
+	else
+		# decode_stacktrace.sh script reports '??:?' with GCC and DWARF5
+		kconfig+=(-e DEBUG_INFO_DWARF4)
+	fi
 
 	# Compressed (old/new option)
 	kconfig+=(-e DEBUG_INFO_COMPRESSED -e DEBUG_INFO_COMPRESSED_ZLIB)

run-tests-clang.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -e
+# SPDX-License-Identifier: GPL-2.0
+DIR="$(dirname "$(realpath -P "${0}")")"
+export INPUT_CLANG=1
+
+bash "-${-}" "${DIR}/run-tests.sh" "${@}"

run-tests-dev-clang.sh

@@ -0,0 +1,6 @@
+#!/bin/bash -ex
+# SPDX-License-Identifier: GPL-2.0
+DIR="$(dirname "$(realpath -P "${0}")")"
+export INPUT_CLANG=1
+
+bash "-${-}" "${DIR}/run-tests-dev.sh" "${@}"

run.sh

@@ -16,6 +16,7 @@ docker run \
 	${VIRTME_PACKETDRILL_PATH:+-v "${VIRTME_PACKETDRILL_PATH}:/opt/packetdrill:rw"} \
 	-v "${HOME_DIR}:/root" \
 	-w "${PWD}" \
+	-e "INPUT_CLANG" \
 	-e "INPUT_TRACE" \
 	-e "INPUT_NO_BLOCK" \
 	-e "INPUT_RUN_LOOP_CONTINUE" \