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Commit 3a2429e1 authored by Masahiro Yamada's avatar Masahiro Yamada
Browse files

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: default avatarMasahiro Yamada <yamada.masahiro@socionext.com>
parent bbda5ec6

scripts/Kbuild.include

+4 −8
Original line number Diff line number Diff line
@@ -215,7 +215,7 @@ echo-cmd = $(if $($(quiet)cmd_$(1)),\ 
	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 @@ if_changed = $(if $(strip $(any-prereq) $(arg-check)), \ 
	printf '%s\n' 'cmd_$@ := $(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

scripts/Makefile.build

+11 −11
Original line number Diff line number Diff line
@@ -260,20 +260,20 @@ cmd_gen_ksymdeps = \ 
endif



define rule_cc_o_c

	$(call echo-cmd,checksrc) $(cmd_checksrc)			  \

	$(call cmd_and_fixdep,cc_o_c)					  \

	$(cmd_gen_ksymdeps)						  \

	$(cmd_checkdoc)							  \

	$(call echo-cmd,objtool) $(cmd_objtool)				  \

	$(cmd_modversions_c)						  \

	$(call echo-cmd,record_mcount) $(cmd_record_mcount)

	$(call cmd,checksrc)

	$(call cmd_and_fixdep,cc_o_c)

	$(call cmd,gen_ksymdeps)

	$(call cmd,checkdoc)

	$(call cmd,objtool)

	$(call cmd,modversions_c)

	$(call cmd,record_mcount)

endef



define rule_as_o_S

	$(call cmd_and_fixdep,as_o_S)					  \

	$(cmd_gen_ksymdeps)						  \

	$(call echo-cmd,objtool) $(cmd_objtool)				  \

	$(cmd_modversions_S)

	$(call cmd_and_fixdep,as_o_S)

	$(call cmd,gen_ksymdeps)

	$(call cmd,objtool)

	$(call cmd,modversions_S)

endef



# List module undefined symbols (or empty line if not enabled)