Under certain conditions, Kbuild shows "... is up to date" where if_changed or friends are used. For example, the incremental build of ARM64 Linux shows this message when the kernel image has not been updated. $ make ARCH=arm64 CROSS_COMPILE=aarch64-linux-gnu- CHK include/config/kernel.release CHK include/generated/uapi/linux/version.h CHK include/generated/utsrelease.h CHK include/generated/bounds.h CHK include/generated/timeconst.h CHK include/generated/asm-offsets.h CALL scripts/checksyscalls.sh CHK include/generated/compile.h CHK kernel/config_data.h make[1]: `arch/arm64/boot/Image.gz' is up to date. Building modules, stage 2. MODPOST 0 modules The following is the build rule in arch/arm64/boot/Makefile: $(obj)/Image.gz: $(obj)/Image FORCE $(call if_changed,gzip) If the Image.gz is newer than the Image and the command line has not changed (i.e., $(any-prereq) and $(arg-check) are both empty), the build rule $(call if_changed,gzip) is evaluated to be empty, then GNU Make reports the target is up to date. In order to make GNU Make quiet, we need to give it something to do, for example, "@:". This should be fixed in the Kbuild core part rather than in each Makefile.
Unified · Split
| @@ -251,7 +251,7 @@ any-prereq = $(filter-out $(PHONY),$?) $(filter-out $(PHONY) $(wildcard $^),$^) · 250 unmodified lines | |||
| 251 | if_changed = $(if $(strip $(any-prereq) $(arg-check)), \ | 251 | if_changed = $(if $(strip $(any-prereq) $(arg-check)), \ |
| 252 | @set -e; \ | 252 | @set -e; \ |
| 253 | $(echo-cmd) $(cmd_$(1)); \ | 253 | $(echo-cmd) $(cmd_$(1)); \ |
| 254 | printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd) | 254 | printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:) |
| 255 | 255 | ||
| 256 | # Execute the command and also postprocess generated .d dependencies file. | 256 | # Execute the command and also postprocess generated .d dependencies file. |
| 257 | if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \ | 257 | if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \ |
| @@ -259,14 +259,14 @@ if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \ · 1 unmodified line | |||
| 259 | $(echo-cmd) $(cmd_$(1)); \ | 259 | $(echo-cmd) $(cmd_$(1)); \ |
| 260 | scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\ | 260 | scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).tmp;\ |
| 261 | rm -f $(depfile); \ | 261 | rm -f $(depfile); \ |
| 262 | mv -f $(dot-target).tmp $(dot-target).cmd) | 262 | mv -f $(dot-target).tmp $(dot-target).cmd, @:) |
| 263 | 263 | ||
| 264 | # Usage: $(call if_changed_rule,foo) | 264 | # Usage: $(call if_changed_rule,foo) |
| 265 | # Will check if $(cmd_foo) or any of the prerequisites changed, | 265 | # Will check if $(cmd_foo) or any of the prerequisites changed, |
| 266 | # and if so will execute $(rule_foo). | 266 | # and if so will execute $(rule_foo). |
| 267 | if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ), \ | 267 | if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ), \ |
| 268 | @set -e; \ | 268 | @set -e; \ |
| 269 | $(rule_$(1))) | 269 | $(rule_$(1)), @:) |
| 270 | 270 | ||
| 271 | ### | 271 | ### |
| 272 | # why - tell why a a target got build | 272 | # why - tell why a a target got build |