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-rw-r--r--Makefile1
-rw-r--r--scripts/Kbuild.include41
2 files changed, 41 insertions, 1 deletions
diff --git a/Makefile b/Makefile
index 22451c2ac1e0..440a1331d883 100644
--- a/Makefile
+++ b/Makefile
@@ -1101,6 +1101,7 @@ help:
echo '')
@echo ' make V=0|1 [targets] 0 => quiet build (default), 1 => verbose build'
+ @echo ' make V=2 [targets] 2 => give reason for rebuild of target'
@echo ' make O=dir [targets] Locate all output files in "dir", including .config'
@echo ' make C=1 [targets] Check all c source with $$CHECK (sparse by default)'
@echo ' make C=2 [targets] Force check of all c source with $$CHECK'
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 1d6ffb26e20f..3d523899fdc0 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -129,7 +129,7 @@ endif
# echo command. Short version is $(quiet) equals quiet, otherwise full command
echo-cmd = $(if $($(quiet)cmd_$(1)), \
- echo ' $(call escsq,$($(quiet)cmd_$(1)))';)
+ echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
# >'< substitution is for echo to work,
# >$< substitution to preserve $ when reloading .cmd file
@@ -164,3 +164,42 @@ if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ), \
@set -e; \
$(rule_$(1)))
+###
+# why - tell why a a target got build
+# enabled by make V=2
+# Output (listed in the order they are checked):
+# (1) - due to target is PHONY
+# (2) - due to target missing
+# (3) - due to: file1.h file2.h
+# (4) - due to command line change
+# (5) - due to missing .cmd file
+# (6) - due to target not in $(targets)
+# (1) PHONY targets are always build
+# (2) No target, so we better build it
+# (3) Prerequisite is newer than target
+# (4) The command line stored in the file named dir/.target.cmd
+# differed from actual command line. This happens when compiler
+# options changes
+# (5) No dir/.target.cmd file (used to store command line)
+# (6) No dir/.target.cmd file and target not listed in $(targets)
+# This is a good hint that there is a bug in the kbuild file
+ifeq ($(KBUILD_VERBOSE),2)
+why = \
+ $(if $(filter $@, $(PHONY)),- due to target is PHONY, \
+ $(if $(wildcard $@), \
+ $(if $(strip $(any-prereq)),- due to: $(any-prereq), \
+ $(if $(arg-check), \
+ $(if $(cmd_$@),- due to command line change, \
+ $(if $(filter $@, $(targets)), \
+ - due to missing .cmd file, \
+ - due to $(notdir $@) not in $$(targets) \
+ ) \
+ ) \
+ ) \
+ ), \
+ - due to target missing \
+ ) \
+ )
+
+echo-why = $(call escsq, $(strip $(why)))
+endif