linux-kernel - [PATCH] s390: disable -Warray-bounds

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Date:   Fri, 22 Apr 2022 15:43:08 +0200
From:   Sven Schnelle <svens@...ux.ibm.com>
To:     Heiko Carstens <hca@...ux.ibm.com>
Cc:     Vasily Gorbik <gor@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] s390: disable -Warray-bounds

gcc-12 shows a lot of array bound warnings on s390. This is caused
by our S390_lowcore macro:

which uses an hardcoded address of 0. Wrapping that with
absolute_pointer() works, but gcc no longer knows that a 12 bit
instruction is sufficient to access lowcore. So it emits instructions
like 'lghi %r1,0; l %rx,xxx(%r1)' instead of a single load/store
instruction. As s390 stores variables often read/written in lowcore,
this is considered problematic. Therefore disable -Warray-bounds on
s390 for now until there is a better real solution.

Signed-off-by: Sven Schnelle <svens@...ux.ibm.com>
---
 arch/s390/Makefile | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/arch/s390/Makefile b/arch/s390/Makefile
index e441b60b1812..aff0f66e25fb 100644
--- a/arch/s390/Makefile
+++ b/arch/s390/Makefile
@@ -14,6 +14,7 @@ KBUILD_AFLAGS_MODULE += -fPIC
 KBUILD_CFLAGS_MODULE += -fPIC
 KBUILD_AFLAGS	+= -m64
 KBUILD_CFLAGS	+= -m64
+KBUILD_CFLAGS	+= $(call cc-disable-warning, array-bounds)
 ifeq ($(CONFIG_RELOCATABLE),y)
 KBUILD_CFLAGS	+= -fPIE
 LDFLAGS_vmlinux	:= -pie
@@ -28,6 +29,7 @@ KBUILD_CFLAGS_DECOMPRESSOR += -fno-asynchronous-unwind-tables
 KBUILD_CFLAGS_DECOMPRESSOR += -ffreestanding
 KBUILD_CFLAGS_DECOMPRESSOR += -fno-stack-protector
 KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, address-of-packed-member)
+KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, array-bounds)
 KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),-g)
 KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO_DWARF4), $(call cc-option, -gdwarf-4,))
 UTS_MACHINE	:= s390x
-- 
2.35.1