linux-kernel - Re: [PATCH early RFC 2/4] kbuild: kasan: refactor open coded cflags for kasan test

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Message-ID: <CANpmjNOJxJ+kM4J7O5J8meSD_V=4uAa6SwFCiG83Vv_8kn56sw@mail.gmail.com>
Date: Tue, 5 Aug 2025 14:30:37 +0200
From: Marco Elver <elver@...gle.com>
To: Jann Horn <jannh@...gle.com>
Cc: Masahiro Yamada <masahiroy@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nicolas Schier <nicolas.schier@...ux.dev>, Andrey Ryabinin <ryabinin.a.a@...il.com>, 
	Alexander Potapenko <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, 
	Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, 
	Andrew Morton <akpm@...ux-foundation.org>, Christoph Lameter <cl@...two.org>, 
	David Rientjes <rientjes@...gle.com>, Vlastimil Babka <vbabka@...e.cz>, 
	Roman Gushchin <roman.gushchin@...ux.dev>, Harry Yoo <harry.yoo@...cle.com>, 
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
	kasan-dev@...glegroups.com, linux-mm@...ck.org
Subject: Re: [PATCH early RFC 2/4] kbuild: kasan: refactor open coded cflags
 for kasan test

On Mon, 4 Aug 2025 at 21:18, Jann Horn <jannh@...gle.com> wrote:
>
> In the Makefile for mm/kasan/, KASAN is broadly disabled to prevent the
> KASAN runtime from recursing into itself; but the KASAN tests must be
> exempt from that.
>
> This is currently implemented by duplicating the same logic that is also
> in scripts/Makefile.lib. In preparation for changing that logic,
> refactor away the duplicate logic - we already have infrastructure for
> opting in specific files inside directories that are opted out.
>
> Signed-off-by: Jann Horn <jannh@...gle.com>
> ---
>  mm/kasan/Makefile | 12 ++----------
>  1 file changed, 2 insertions(+), 10 deletions(-)
>
> diff --git a/mm/kasan/Makefile b/mm/kasan/Makefile
> index dd93ae8a6beb..922b2e6f6d14 100644
> --- a/mm/kasan/Makefile
> +++ b/mm/kasan/Makefile
> @@ -35,18 +35,10 @@ CFLAGS_shadow.o := $(CC_FLAGS_KASAN_RUNTIME)
>  CFLAGS_hw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
>  CFLAGS_sw_tags.o := $(CC_FLAGS_KASAN_RUNTIME)
>
> -CFLAGS_KASAN_TEST := $(CFLAGS_KASAN)
> -ifndef CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX
> -# If compiler instruments memintrinsics by prefixing them with __asan/__hwasan,
> -# we need to treat them normally (as builtins), otherwise the compiler won't
> -# recognize them as instrumentable. If it doesn't instrument them, we need to
> -# pass -fno-builtin, so the compiler doesn't inline them.
> -CFLAGS_KASAN_TEST += -fno-builtin

Has the -fno-builtin passed to test if
!CONFIG_CC_HAS_KASAN_MEMINTRINSIC_PREFIX become redundant?


> -endif
> +KASAN_SANITIZE_kasan_test_c.o := y
> +KASAN_SANITIZE_kasan_test_rust.o := y
>
>  CFLAGS_REMOVE_kasan_test_c.o += $(call cc-option, -Wvla-larger-than=1)
> -CFLAGS_kasan_test_c.o := $(CFLAGS_KASAN_TEST)
> -RUSTFLAGS_kasan_test_rust.o := $(RUSTFLAGS_KASAN)
>
>  obj-y := common.o report.o
>  obj-$(CONFIG_KASAN_GENERIC) += init.o generic.o report_generic.o shadow.o quarantine.o
>
> --
> 2.50.1.565.gc32cd1483b-goog
>