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 4b943f4d22264d09ec758f320c90efc86ec374f8..6bbbe7533d6ff633ce8515f01aec980fb20e150f 100644 (file)
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -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

diff --git a/scripts/Makefile.build b/scripts/Makefile.build
index 23ebf2508234287cddce1b54457fd1c3ce5f78c4..a0002246366bec5e35e97b9501031451b11ef51f 100644 (file)
--- a/scripts/Makefile.build
+++ b/scripts/Makefile.build
@@ -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)