kpatch-build: add cross-compilation support

This patch introduces ability to pick a CROSS_COMPILE
environment variable which can be used for
specifying toolchain prefix for all gcc utils
(gcc, ld, objcopy etc).
DISTRO checks are disabled if VMLINUX and USERSRCDIR
are specified.

Author: rbilovol

kpatch-build/kpatch-build

@@ -278,7 +278,7 @@ gcc_version_check() {
 	# gcc --version varies between distributions therefore extract version
 	# by compiling a test file and compare it to vmlinux's version.
 	echo 'void main(void) {}' > "$c"
-	out="$(gcc -c -pg -ffunction-sections -o "$o" "$c" 2>&1)"
+	out="$("${CROSS_COMPILE}"gcc -c -pg -ffunction-sections -o "$o" "$c" 2>&1)"
 	gccver="$(gcc_version_from_file "$o")"
 	kgccver="$(gcc_version_from_file "$target")"
 
@@ -656,6 +656,14 @@ mkdir -p "$TEMPDIR" || die "Couldn't create $TEMPDIR"
 rm -rf "${TEMPDIR:?}"/*
 rm -f "$LOGFILE"
 
+
+if [[ -n "$USERSRCDIR" ]] && [[ -n "$VMLINUX" ]]; then
+	DISTRO="dummy" # I think some of the DISTRO checks could be skipped, given the user provides source dir and vmlinux files.
+else 
+	DISTRO="$ID"
+fi
+
+
 if [[ -n "$USERSRCDIR" ]]; then
 	if [[ -n "$ARCHVERSION" ]]; then
 		warn "--archversion is incompatible with --sourcedir"
@@ -699,7 +707,8 @@ fi
 # Don't check external file.
 # shellcheck disable=SC1090
 [[ -f "$RELEASE_FILE" ]] && source "$RELEASE_FILE"
-DISTRO="$ID"
+
+
 if [[ "$DISTRO" = fedora ]] || [[ "$DISTRO" = rhel ]] || [[ "$DISTRO" = ol ]] || [[ "$DISTRO" = centos ]] || [[ "$DISTRO" = openEuler ]]; then
 	[[ -z "$VMLINUX" ]] && VMLINUX="/usr/lib/debug/lib/modules/$ARCHVERSION/vmlinux"
 	[[ -e "$VMLINUX" ]] || die "kernel-debuginfo-$ARCHVERSION not installed"
@@ -929,17 +938,17 @@ unset KPATCH_GCC_TEMPDIR
 KPATCH_CC_PREFIX="$TOOLSDIR/kpatch-cc "
 declare -a MAKEVARS
 if [[ -n "$CONFIG_CC_IS_CLANG" ]]; then
-	MAKEVARS+=("CC=${KPATCH_CC_PREFIX}clang")
+	MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${CROSS_COMPILE}clang")
 	MAKEVARS+=("HOSTCC=clang")
 else
-	MAKEVARS+=("CC=${KPATCH_CC_PREFIX}gcc")
+	MAKEVARS+=("CC=${KPATCH_CC_PREFIX}${CROSS_COMPILE}gcc")
 fi
 
 if [[ -n "$CONFIG_LD_IS_LLD" ]]; then
-	MAKEVARS+=("LD=${KPATCH_CC_PREFIX}ld.lld")
+	MAKEVARS+=("LD=${KPATCH_CC_PREFIX}${CROSS_COMPILE}ld.lld")
 	MAKEVARS+=("HOSTLD=ld.lld")
 else
-	MAKEVARS+=("LD=${KPATCH_CC_PREFIX}ld")
+	MAKEVARS+=("LD=${KPATCH_CC_PREFIX}${CROSS_COMPILE}ld")
 fi
 
 
@@ -1129,7 +1138,7 @@ fi
 cd "$TEMPDIR/output" || die
 # $KPATCH_LDFLAGS and result of find used as list, no quotes.
 # shellcheck disable=SC2086,SC2046
-ld -r $KPATCH_LDFLAGS -o ../patch/tmp_output.o $(find . -name "*.o") 2>&1 | logger || die
+"$CROSS_COMPILE"ld -r $KPATCH_LDFLAGS -o ../patch/tmp_output.o $(find . -name "*.o") 2>&1 | logger || die
 
 if [[ "$USE_KLP" -eq 1 ]]; then
 	cp -f "$TEMPDIR"/patch/tmp_output.o "$TEMPDIR"/patch/output.o || die
@@ -1138,7 +1147,7 @@ if [[ "$USE_KLP" -eq 1 ]]; then
 else
 	# Add .kpatch.checksum for kpatch script
 	md5sum ../patch/tmp_output.o | awk '{printf "%s\0", $1}' > checksum.tmp || die
-	objcopy --add-section .kpatch.checksum=checksum.tmp --set-section-flags .kpatch.checksum=alloc,load,contents,readonly  ../patch/tmp_output.o || die
+	"$CROSS_COMPILE"objcopy --add-section .kpatch.checksum=checksum.tmp --set-section-flags .kpatch.checksum=alloc,load,contents,readonly  ../patch/tmp_output.o || die
 	rm -f checksum.tmp
 	"$TOOLSDIR"/create-kpatch-module "$TEMPDIR"/patch/tmp_output.o "$TEMPDIR"/patch/output.o 2>&1 | logger 1
 	check_pipe_status create-kpatch-module
@@ -1154,7 +1163,8 @@ done
 
 export KPATCH_BUILD="$KERNEL_SRCDIR" KPATCH_NAME="$MODNAME" \
 KBUILD_EXTRA_SYMBOLS="$KBUILD_EXTRA_SYMBOLS" \
-KPATCH_LDFLAGS="$KPATCH_LDFLAGS"
+KPATCH_LDFLAGS="$KPATCH_LDFLAGS" \
+CROSS_COMPILE="$CROSS_COMPILE"
 save_env
 
 make "${MAKEVARS[@]}" 2>&1 | logger || die