kbuild: add CONFIG_VMLINUX_MAP expert option

It can be quite useful to have ld emit a link map file, in order to
debug or verify that special sections end up where they are supposed
to, and to see what LD_DEAD_CODE_DATA_ELIMINATION manages to get rid
of.

The only reason I'm not just adding this unconditionally is that the
.map file can be rather large (several MB), and that's a waste of
space when one isn't interested in these things. Also make it depend
on CONFIG_EXPERT.

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

scripts/link-vmlinux.sh

@@ -155,6 +155,7 @@ vmlinux_link()
 	local output=${1}
 	local objects
 	local strip_debug
+	local map_option
 
 	info LD ${output}
 
@@ -166,6 +167,10 @@ vmlinux_link()
 		strip_debug=-Wl,--strip-debug
 	fi
 
+	if [ -n "${CONFIG_VMLINUX_MAP}" ]; then
+		map_option="-Map=${output}.map"
+	fi
+
 	if [ "${SRCARCH}" != "um" ]; then
 		if [ -n "${CONFIG_LTO_CLANG}" ]; then
 			# Use vmlinux.o instead of performing the slow LTO
@@ -187,6 +192,7 @@ vmlinux_link()
 		${LD} ${KBUILD_LDFLAGS} ${LDFLAGS_vmlinux}	\
 			${strip_debug#-Wl,}			\
 			-o ${output}				\
+			${map_option}				\
 			-T ${lds} ${objects}
 	else
 		objects="-Wl,--whole-archive			\
@@ -200,6 +206,7 @@ vmlinux_link()
 		${CC} ${CFLAGS_vmlinux}				\
 			${strip_debug}				\
 			-o ${output}				\
+			${map_option:+-Wl,${map_option}}	\
 			-Wl,-T,${lds}				\
 			${objects}				\
 			-lutil -lrt -lpthread
@@ -303,6 +310,7 @@ cleanup()
 	rm -f .tmp_vmlinux*
 	rm -f System.map
 	rm -f vmlinux
+	rm -f vmlinux.map
 	rm -f vmlinux.o
 }