linux-kernel - Re: [PATCH v3 2/5] kasan/Makefile: Support LLVM style asan parameters.

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Date:   Mon, 4 Dec 2017 19:55:15 +0300
From:   Andrey Ryabinin <aryabinin@...tuozzo.com>
To:     Paul Lawrence <paullawrence@...gle.com>
Cc:     Alexander Potapenko <glider@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, linux-kbuild@...r.kernel.org,
        Matthias Kaehlcke <mka@...omium.org>,
        Michael Davidson <md@...gle.com>,
        Greg Hackmann <ghackmann@...gle.com>
Subject: Re: [PATCH v3 2/5] kasan/Makefile: Support LLVM style asan
 parameters.

On 12/04/2017 07:20 PM, Paul Lawrence wrote:

> 
>     > +   # -fasan-shadow-offset fails without -fsanitize
>     > +   CFLAGS_KASAN_SHADOW := $(call cc-option, -fsanitize=kernel-address \
>     > +                     -fasan-shadow-offset=$(KASAN_SHADOW_OFFSET), \
>     > +                     $(call cc-option, -fsanitize=kernel-address \
>     > +                     -mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
>     > +
>     > +   ifeq ("$(CFLAGS_KASAN_SHADOW)"," ")
> 
>     This not how it was in my original patch. Why you changed this?
>     Condition is always false now, so it breaks kasan with 4.9.x gcc.
> 
> 
> I had the opposite problem - CFLAGS_KASAN_SHADOW is always at least a space, and the
> original condition would always be false, which is why I changed it. On investigation, I found 
> that if the line was split it would always be a space - $(false,whatever,empty-string) would be
> truly empty, but if the line was split after the second comma it would be one space. Is this a
> difference in our make systems?

I dunno, but it could be.
Anyways, does the fixup bellow works for you?

---
 scripts/Makefile.kasan | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/scripts/Makefile.kasan b/scripts/Makefile.kasan
index 7c00be9216f4..d5a1a4b6d079 100644
--- a/scripts/Makefile.kasan
+++ b/scripts/Makefile.kasan
@@ -24,7 +24,7 @@ else
 			$(call cc-option, -fsanitize=kernel-address \
 			-mllvm -asan-mapping-offset=$(KASAN_SHADOW_OFFSET)))
 
-   ifeq ("$(CFLAGS_KASAN_SHADOW)"," ")
+   ifeq ($(strip $(CFLAGS_KASAN_SHADOW)),)
       CFLAGS_KASAN := $(CFLAGS_KASAN_MINIMAL)
    else
       # Now add all the compiler specific options that are valid standalone
-- 
2.13.6