kbuild: change if_changed_rule for multi-line recipe
The 'define' ... 'endef' directive is useful to confine a series of
shell commands into a single macro:
define foo
[action1]
[action2]
[action3]
endif
Each action is executed in a separate subshell.
However, rule_cc_o_c and rule_as_o_S in scripts/Makefile.build are
written as follows (with a trailing semicolon in each cmd_*):
define rule_cc_o_c
[action1] ; \
[action2] ; \
[action3] ;
endef
All shell commands are concatenated with '; \' so that it looks like
a single command from the Makefile point of view. This does not
exploit the benefits of 'define' ... 'endef' form because a single
shell command can be more simply written, like this:
rule_cc_o_c = \
[action1] ; \
[action2] ; \
[action3] ;
I guess the intention for the command concatenation was to let the
'@set -e' in if_changed_rule cover all the commands.
We can improve the readability by moving '@set -e' to the 'cmd' macro.
The combo of $(call echo-cmd,*) $(cmd_*) in rule_cc_o_c and rule_as_o_S
have been replaced with $(call cmd,*). The trailing back-slashes have
been removed.
Here is a note about the performance: the commands in rule_cc_o_c and
rule_as_o_S were previously executed all together in a single subshell,
but now each line in a separate subshell. This means Make will spawn
extra subshells [1]. I measured the build performance for
x86_64_defconfig + CONFIG_MODVERSIONS + CONFIG_TRIM_UNUSED_KSYMS
and I saw slight performance regression, but I believe code readability
and maintainability wins.
[1] Precisely, GNU Make may optimize this by executing the command
directly instead of forking a subshell, if no shell special
characters are found in the command line and omitting the subshell
will not change the behavior.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index 4b943f4..6bbbe75 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -215,7 +215,7 @@
echo ' $(call escsq,$($(quiet)cmd_$(1)))$(echo-why)';)
# printing commands
-cmd = @$(echo-cmd) $(cmd_$(1))
+cmd = @set -e; $(echo-cmd) $(cmd_$(1))
# Add $(obj)/ for paths that are not absolute
objectify = $(foreach o,$(1),$(if $(filter /%,$(o)),$(o),$(obj)/$(o)))
@@ -256,21 +256,17 @@
printf '%s\n' 'cmd_$@ := $(make-cmd)' > $(dot-target).cmd, @:)
# Execute the command and also postprocess generated .d dependencies file.
-if_changed_dep = $(if $(strip $(any-prereq) $(arg-check) ), \
- @set -e; \
- $(cmd_and_fixdep), @:)
+if_changed_dep = $(if $(strip $(any-prereq) $(arg-check)),$(cmd_and_fixdep),@:)
cmd_and_fixdep = \
- $(echo-cmd) $(cmd_$(1)); \
+ $(cmd); \
scripts/basic/fixdep $(depfile) $@ '$(make-cmd)' > $(dot-target).cmd;\
rm -f $(depfile);
# Usage: $(call if_changed_rule,foo)
# Will check if $(cmd_foo) or any of the prerequisites changed,
# and if so will execute $(rule_foo).
-if_changed_rule = $(if $(strip $(any-prereq) $(arg-check) ), \
- @set -e; \
- $(rule_$(1)), @:)
+if_changed_rule = $(if $(strip $(any-prereq) $(arg-check)),$(rule_$(1)),@:)
###
# why - tell why a target got built