Subject: Re: [PATCH v3 2/5] kasan/Makefile: Support LLVM style asan
 parameters.
To: Paul Lawrence <paullawrence@google.com>
Cc: Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com,
        linux-mm@kvack.org, linux-kbuild@vger.kernel.org,
        Matthias Kaehlcke <mka@chromium.org>, Michael Davidson <md@google.com>,
        Greg Hackmann <ghackmann@google.com>
References: <20171201213643.2506-1-paullawrence@google.com>
 <20171201213643.2506-3-paullawrence@google.com>
 <33f13b1a-494c-67d5-a470-294867c06f9a@virtuozzo.com>
 <CAL=UVf7LO5BDWVEeLXLkrLDBxwV0aO2sLv_htkpcL_Gp7sT07Q@mail.gmail.com>
From: Andrey Ryabinin <aryabinin@virtuozzo.com>
Message-ID: <2da6480e-08ff-2444-7abf-2964de53e7ff@virtuozzo.com>
Date: Mon, 4 Dec 2017 19:55:15 +0300
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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