[PATCH] kbuild: add Map option to save vmlinux linker map file(s)

[Vasily Gorbik]

Add "Map" kbuild option, so that "make Map=1" would save vmlinux linker
map into vmlinux.map, which is quite useful during making kernel changes
related to how the kernel is composed.

KBUILD_SAVE_LINK_MAP flag is exported and architectures
supporting compressed kernel images might respect it and produce
arch/*/boot/compressed/vmlinux.map for the decompressor code as well.

Signed-off-by: Vasily Gorbik <gor@xxxxxxxxxxxxx>
---
 .gitignore |  1 +
 Makefile   | 14 ++++++++++++++
 2 files changed, 15 insertions(+)

diff --git a/.gitignore b/.gitignore
index 97ba6b79834c..1d2308e597ad 100644
--- a/.gitignore
+++ b/.gitignore
@@ -44,6 +44,7 @@
 *.xz
 Module.symvers
 modules.builtin
+vmlinux.map
 
 #
 # Top-level generic files
diff --git a/Makefile b/Makefile
index 7a3c4548162b..f1790deae03b 100644
--- a/Makefile
+++ b/Makefile
@@ -176,6 +176,14 @@ ifndef KBUILD_CHECKSRC
   KBUILD_CHECKSRC = 0
 endif
 
+# Use 'make Map=1' to enable saving linker map file(s):
+# vmlinux.map for vmlinux,
+# (arch/*/boot/compressed/vmlinux.map for arch/*/boot/compressed/vmlinux)
+
+ifeq ("$(origin Map)", "command line")
+	export KBUILD_SAVE_LINK_MAP := $(Map)
+endif
+
 # Use make M=dir to specify directory of external module to build
 # Old syntax make ... SUBDIRS=$PWD is still supported
 # Setting the environment variable KBUILD_EXTMOD take precedence
@@ -838,6 +846,11 @@ ifeq ($(CONFIG_STRIP_ASM_SYMS),y)
 LDFLAGS_vmlinux	+= $(call ld-option, -X,)
 endif
 
+ifdef KBUILD_SAVE_LINK_MAP
+LDFLAGS_vmlinux	+= -Map=vmlinux.map
+CLEAN_FILES	+= vmlinux.map
+endif
+
 # insure the checker run with the right endianness
 CHECKFLAGS += $(if $(CONFIG_CPU_BIG_ENDIAN),-mbig-endian,-mlittle-endian)
 
@@ -1434,6 +1447,7 @@ help:
 	@echo  '		2: warnings which occur quite often but may still be relevant'
 	@echo  '		3: more obscure warnings, can most likely be ignored'
 	@echo  '		Multiple levels can be combined with W=12 or W=123'
+	@echo  '  make Map=1 [targets] Save vmlinux linker map file(s)'
 	@echo  ''
 	@echo  'Execute "make" or "make all" to build all targets marked with [*] '
 	@echo  'For further info see the ./README file'
-- 
2.18.0.13.gd42ae10