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 when gcc-12 is used until there is a better real solution.

Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
---
Changes in v2:
- only remove -Warray-bounds for gcc-12

 arch/s390/Makefile | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/s390/Makefile b/arch/s390/Makefile
index e441b60b1812..df325eacf62d 100644
--- a/arch/s390/Makefile
+++ b/arch/s390/Makefile
@@ -30,6 +30,16 @@ KBUILD_CFLAGS_DECOMPRESSOR += -fno-stack-protector
 KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, address-of-packed-member)
 KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO),-g)
 KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_DEBUG_INFO_DWARF4), $(call cc-option, -gdwarf-4,))
+
+ifdef CONFIG_CC_IS_GCC
+	ifeq ($(call cc-ifversion, -ge, 1200, y), y)
+		ifeq ($(call cc-ifversion, -lt, 1300, y), y)
+			KBUILD_CFLAGS += $(call cc-disable-warning, array-bounds)
+			KBUILD_CFLAGS_DECOMPRESSOR += $(call cc-disable-warning, array-bounds)
+		endif
+	endif
+endif
+
 UTS_MACHINE	:= s390x
 STACK_SIZE	:= $(if $(CONFIG_KASAN),65536,16384)
 CHECKFLAGS	+= -D__s390__ -D__s390x__
-- 
2.35.1

On Mon, Apr 25, 2022 at 02:17:42PM +0200, Sven Schnelle wrote:
> 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 when gcc-12 is used until there is a better real solution.
> 
> Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
> ---
> Changes in v2:
> - only remove -Warray-bounds for gcc-12
> 
>  arch/s390/Makefile | 10 ++++++++++
>  1 file changed, 10 insertions(+)

Applied, thanks!