linux-kernel - [PATCH 2/2] kbuild: move CFLAGS_{KASAN,UBSAN,KCSAN} exports to relevant Makefiles

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Date:   Thu, 10 Sep 2020 22:44:29 +0900
From:   Masahiro Yamada <masahiroy@...nel.org>
To:     linux-kbuild@...r.kernel.org
Cc:     Ingo Molnar <mingo@...hat.com>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Marco Elver <elver@...gle.com>,
        Michal Marek <michal.lkml@...kovi.net>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] kbuild: move CFLAGS_{KASAN,UBSAN,KCSAN} exports to relevant Makefiles

Move CFLAGS_KASAN*, CFLAGS_UBSAN, CFLAGS_KCSAN to Makefile.kasan,
Makefile.ubsan, Makefile.kcsan, respectively.

This commit also avoids the same -fsanitize=* flags being added to
CFLAGS_UBSAN multiple times.

Prior to this commit, the ubsan flags were appended by the '+='
operator, without any initialization. Some build targets such as
'make bindeb-pkg' recurses to the top Makefile, and ended up with
adding the same flags to CFLAGS_UBSAN twice.

Clear CFLAGS_UBSAN with ':=' to make it a simply expanded variable.
This is better than a recursively expanded variable, which evaluates
$(call cc-option, ...) multiple times before Kbuild starts descending
to subdirectories.

Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>
---

 Makefile               | 1 -
 scripts/Makefile.kasan | 2 ++
 scripts/Makefile.kcsan | 2 +-
 scripts/Makefile.ubsan | 3 +++
 4 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index ec2330ce0fc5..4b5a305e30d2 100644
--- a/Makefile
+++ b/Makefile
@@ -517,7 +517,6 @@ export KBUILD_HOSTCXXFLAGS KBUILD_HOSTLDFLAGS KBUILD_HOSTLDLIBS LDFLAGS_MODULE
 
 export KBUILD_CPPFLAGS NOSTDINC_FLAGS LINUXINCLUDE OBJCOPYFLAGS KBUILD_LDFLAGS
 export KBUILD_CFLAGS CFLAGS_KERNEL CFLAGS_MODULE
-export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE CFLAGS_UBSAN CFLAGS_KCSAN
 export KBUILD_AFLAGS AFLAGS_KERNEL AFLAGS_MODULE
 export KBUILD_AFLAGS_MODULE KBUILD_CFLAGS_MODULE KBUILD_LDFLAGS_MODULE
 export KBUILD_AFLAGS_KERNEL KBUILD_CFLAGS_KERNEL
diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 1532f1a41a8f..1e000cc2e7b4 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -47,3 +47,5 @@ CFLAGS_KASAN := -fsanitize=kernel-hwaddress \
 		$(instrumentation_flags)
 
 endif # CONFIG_KASAN_SW_TAGS
+
+export CFLAGS_KASAN CFLAGS_KASAN_NOSANITIZE
diff --git a/scripts/Makefile.kcsan b/scripts/Makefile.kcsan
index c50f27b3ac56..cec50d74e0d0 100644
--- a/scripts/Makefile.kcsan
+++ b/scripts/Makefile.kcsan
@@ -9,7 +9,7 @@ endif
 
 # Keep most options here optional, to allow enabling more compilers if absence
 # of some options does not break KCSAN nor causes false positive reports.
-CFLAGS_KCSAN := -fsanitize=thread \
+export CFLAGS_KCSAN := -fsanitize=thread \
 	$(call cc-option,$(call cc-param,tsan-instrument-func-entry-exit=0) -fno-optimize-sibling-calls) \
 	$(call cc-option,$(call cc-param,tsan-instrument-read-before-write=1)) \
 	$(call cc-param,tsan-distinguish-volatile=1)
diff --git a/scripts/Makefile.ubsan b/scripts/Makefile.ubsan
index 27348029b2b8..c661484ee01f 100644
--- a/scripts/Makefile.ubsan
+++ b/scripts/Makefile.ubsan
@@ -1,4 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
+
+export CFLAGS_UBSAN :=
+
 ifdef CONFIG_UBSAN_ALIGNMENT
       CFLAGS_UBSAN += $(call cc-option, -fsanitize=alignment)
 endif
-- 
2.25.1