livepatch-cc

#!/usr/bin/env bash
#
# Copyright 2021 Google LLC
# 
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# 
#     https://www.apache.org/licenses/LICENSE-2.0
# 
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#
# Author: yonghyun@google.com (Yonghyun Hwang)
#
# This script intercepts CC command for kbuild's dir/file.o targets to compiles a LLVM IR
# FILE. For the dir/file.o target, it replaces .c file with a LLVM IR file that distills
# diffs between 'original' and 'patched'. This task is required to compile the IR file
# with the same compilation flags as .c file.

#-------------------------------------------------------------
# Shell setting
#-------------------------------------------------------------
set -E

#-------------------------------------------------------------
# Global variables
#-------------------------------------------------------------
declare -r G_KLP_DIFF_SUFFIX='__klp_diff.ll'
declare -r G_KLP_OBJ_SUFFIX='__klp_diff.o'

#-------------------------------------------------------------
# Function definitions
#-------------------------------------------------------------
function util::log_error()
{
	echo "${G_LOG_HEADER}[ERR |$(date +'%m/%d %H:%M')]:: $@" >&2
	return 0
}

function util::error()
{
	util::log_error "$@"
	return 1
}

function util::cleanup()
{
	local errCode="${1:-}"
	local lineNum="${2:-}"

	[[ ${errCode} == 0 ]] || \
		util::log_error "trap at line: ${lineNum}, with error:${errCode}."

	exit "${errCode}"
}
# enable exit trap for debugging purpose
trap 'util::cleanup $? ${LINENO}' ERR INT TERM EXIT

#-------------------------------------------------------------
# Main starts here
#-------------------------------------------------------------
declare -r CC_CMD="${1}"
shift
declare -ar ORIG_ARGS=("$@")

if [[ -z "${LIVEPATCH_COMPILE_PARAMS}" ]]; then
	# empty ${LIVEPATCH_COMPILE_PARAMS} means livepatch-cc is expected to
	# pass through a command.
	exec "${CC_CMD}" "${ORIG_ARGS[@]}"
fi

# .ll file is used to compute diff between original and patched. "-g" option makes clang
# to generate calls to llvm.dbg.*. This results in unnecessary diffs between the original
# and patched. So, removing "-g" options here.
if [[ "${LIVEPATCH_COMPILE_PARAMS}" == "build_ll_file" ]]; then
	declare -a args=()
	while [ "$#" -gt 0 ]; do
		if [[ "${1}" != "-g" ]]; then
			args+=("${1}")
		fi
		shift
	done
	exec "${CC_CMD}" "${args[@]}"
fi

# for now, ${LIVEPATCH_COMPILE_PARAMS} == "build_distilled_file" means livepatch-cc is
# expected to compile a LLVM IR file. At this point, kbuild thinks that it builds .c
# file. So, livepatch-cc replaces .c file w/ LLVM IR file that distills the diffs for
# kernel livepatch generation.
declare -a args=()
declare llvm_diff_file=""
while [ "$#" -gt 0 ]; do
	if [[ -f "${1}" ]]; then
		[[ -z "${llvm_diff_file}" ]] || \
			util::error "cannot have two .c files on a single command"

		if [[ -f "${1}${G_KLP_DIFF_SUFFIX}" ]]; then
			# now, located .c file. replace it w/ LLVM IR file. note that
			# this LLVM IR file should be already created by `livepatch
			# diff` command.
			llvm_diff_file="${1}"
			args+=("${llvm_diff_file}${G_KLP_DIFF_SUFFIX}")
		else
			args+=("${1}")
		fi
	else
		args+=("${1}")
	fi
	shift
done

if [[ -z "${llvm_diff_file}" ]]; then
	# kbuild builds other files due to a dependancy. pass through a command.
	exec "${CC_CMD}" "${ORIG_ARGS[@]}"
fi

# because kbuild expects outputs, such as dir/file.d, for dir/file.o target,
# run an original command first.
"${CC_CMD}" "${ORIG_ARGS[@]}"
# note that the last -o option is picked up by compiler for output
# filename.
args+=("-o" "${llvm_diff_file}${G_KLP_OBJ_SUFFIX}")
exec "${CC_CMD}" "${args[@]}"