linux-kernel - [PATCH] kbuild: fix if_change and friends to consider argument order

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Date:	Thu,  5 May 2016 16:45:12 +0900
From:	Masahiro Yamada <yamada.masahiro@...ionext.com>
To:	linux-kbuild@...r.kernel.org
Cc:	Masahiro Yamada <yamada.masahiro@...ionext.com>,
	Michal Marek <mmarek@...e.com>,
	David Howells <dhowells@...hat.com>,
	David Woodhouse <David.Woodhouse@...el.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] kbuild: fix if_change and friends to consider argument order

Currently, arg-check is implemented as follows:

  arg-check = $(strip $(filter-out $(cmd_$(1)), $(cmd_$@)) \
                      $(filter-out $(cmd_$@),   $(cmd_$(1))) )

This does not care about the order of arguments that appear in
$(cmd_$(1)) and $(cmd_$@).  So, if_changed and friends never rebuild
the target if only the argument order is changed.  This is a problem
when the link order is changed.

Apparently,

  obj-y += foo.o
  obj-y += bar.o

and

  obj-y += bar.o
  obj-y += foo.o

should be distinguished because the link order determines the probe
order of drivers.  So, built-in.o should be rebuilt if the order of
objects is changed.

This commit fixes arg-check to compare two strings as a whole.
$(strip ...) is important because we want to ignore the difference
that comes from white-spaces.

Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
---

 scripts/Kbuild.include | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/scripts/Kbuild.include b/scripts/Kbuild.include
index b2ab2a9..2d03480 100644
--- a/scripts/Kbuild.include
+++ b/scripts/Kbuild.include
@@ -228,8 +228,8 @@ objectify = $(foreach o,$(1),$(if $(filter /%,$(o)),$(o),$(obj)/$(o)))
 ifneq ($(KBUILD_NOCMDDEP),1)
 # Check if both arguments has same arguments. Result is empty string if equal.
 # User may override this check using make KBUILD_NOCMDDEP=1
-arg-check = $(strip $(filter-out $(cmd_$(1)), $(cmd_$@)) \
-                    $(filter-out $(cmd_$@),   $(cmd_$(1))) )
+arg-check = $(filter-out $(quote)$(strip $(cmd_$1))$(quote), \
+                         $(quote)$(strip $(cmd_$@))$(quote))
 else
 arg-check = $(if $(strip $(cmd_$@)),,1)
 endif
-- 
1.9.1