kbuild: split adjust_autoksyms.sh in two parts

In order to prepare the ground for a build-time optimization, split
adjust_autoksyms.sh into two scripts: one that generates autoksyms.h
based on all currently available information (whitelist, and .mod
files), and the other to inspect the diff between two versions of
autoksyms.h and trigger appropriate rebuilds.
Acked-by: Nicolas Pitre <nico@fluxnic.net>
Tested-by: Matthias Maennich <maennich@google.com>
Reviewed-by: Matthias Maennich <maennich@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/adjust_autoksyms.sh

 #!/bin/sh
 # SPDX-License-Identifier: GPL-2.0-only
 
-# Script to create/update include/generated/autoksyms.h and dependency files
+# Script to update include/generated/autoksyms.h and dependency files
 #
 # Copyright:	(C) 2016  Linaro Limited
 # Created by:	Nicolas Pitre, January 2016
 #
 
-# Create/update the include/generated/autoksyms.h file from the list
-# of all module's needed symbols as recorded on the second line of *.mod files.
+# Update the include/generated/autoksyms.h file.
 #
 # For each symbol being added or removed, the corresponding dependency
 # file's timestamp is updated to force a rebuild of the affected source
@@ -38,35 +37,8 @@ esac
 # We need access to CONFIG_ symbols
 . include/config/auto.conf
 
-ksym_wl=/dev/null
-if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then
-	# Use 'eval' to expand the whitelist path and check if it is relative
-	eval ksym_wl="$CONFIG_UNUSED_KSYMS_WHITELIST"
-	[ "${ksym_wl}" != "${ksym_wl#/}" ] || ksym_wl="$abs_srctree/$ksym_wl"
-	if [ ! -f "$ksym_wl" ] || [ ! -r "$ksym_wl" ]; then
-		echo "ERROR: '$ksym_wl' whitelist file not found" >&2
-		exit 1
-	fi
-fi
-
-# Generate a new ksym list file with symbols needed by the current
-# set of modules.
-cat > "$new_ksyms_file" << EOT
-/*
- * Automatically generated file; DO NOT EDIT.
- */
-
-EOT
-sed 's/ko$/mod/' modules.order |
-xargs -n1 sed -n -e '2{s/ /\n/g;/^$/!p;}' -- |
-cat - "$ksym_wl" |
-sort -u |
-sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$new_ksyms_file"
-
-# Special case for modversions (see modpost.c)
-if [ -n "$CONFIG_MODVERSIONS" ]; then
-	echo "#define __KSYM_module_layout 1" >> "$new_ksyms_file"
-fi
+# Generate a new symbol list file
+$CONFIG_SHELL $srctree/scripts/gen_autoksyms.sh "$new_ksyms_file"
 
 # Extract changes between old and new list and touch corresponding
 # dependency files.

scripts/gen_autoksyms.sh

+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-only
+
+# Create an autoksyms.h header file from the list of all module's needed symbols
+# as recorded on the second line of *.mod files and the user-provided symbol
+# whitelist.
+
+set -e
+
+output_file="$1"
+
+# Use "make V=1" to debug this script.
+case "$KBUILD_VERBOSE" in
+*1*)
+	set -x
+	;;
+esac
+
+# We need access to CONFIG_ symbols
+. include/config/auto.conf
+
+ksym_wl=/dev/null
+if [ -n "$CONFIG_UNUSED_KSYMS_WHITELIST" ]; then
+	# Use 'eval' to expand the whitelist path and check if it is relative
+	eval ksym_wl="$CONFIG_UNUSED_KSYMS_WHITELIST"
+	[ "${ksym_wl}" != "${ksym_wl#/}" ] || ksym_wl="$abs_srctree/$ksym_wl"
+	if [ ! -f "$ksym_wl" ] || [ ! -r "$ksym_wl" ]; then
+		echo "ERROR: '$ksym_wl' whitelist file not found" >&2
+		exit 1
+	fi
+fi
+
+# Generate a new ksym list file with symbols needed by the current
+# set of modules.
+cat > "$output_file" << EOT
+/*
+ * Automatically generated file; DO NOT EDIT.
+ */
+
+EOT
+
+sed 's/ko$/mod/' modules.order |
+xargs -n1 sed -n -e '2{s/ /\n/g;/^$/!p;}' -- |
+cat - "$ksym_wl" |
+sort -u |
+sed -e 's/\(.*\)/#define __KSYM_\1 1/' >> "$output_file"
+
+# Special case for modversions (see modpost.c)
+if [ -n "$CONFIG_MODVERSIONS" ]; then
+	echo "#define __KSYM_module_layout 1" >> "$output_file"
+fi