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

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Message-Id: <20250804-kasan-via-kcsan-v1-2-823a6d5b5f84@google.com>
Date: Mon, 04 Aug 2025 21:17:06 +0200
From: Jann Horn <jannh@...gle.com>
To: 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>, Marco Elver <elver@...gle.com>, 
 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>
Cc: linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org, 
 kasan-dev@...glegroups.com, linux-mm@...ck.org, 
 Jann Horn <jannh@...gle.com>
Subject: [PATCH early RFC 2/4] kbuild: kasan: refactor open coded cflags
 for kasan test

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
-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