gcc-12: disable '-Warray-bounds' universally for now

In commit 8b202ee ("s390: disable -Warray-bounds") the s390 people
disabled the '-Warray-bounds' warning for gcc-12, because the new logic
in gcc would cause warnings for their use of the S390_lowcore macro,
which accesses absolute pointers.

It turns out gcc-12 has many other issues in this area, so this takes
that s390 warning disable logic, and turns it into a kernel build config
entry instead.

Part of the intent is that we can make this all much more targeted, and
use this conflig flag to disable it in only particular configurations
that cause problems, with the s390 case as an example:

        select GCC12_NO_ARRAY_BOUNDS

and we could do that for other configuration cases that cause issues.

Or we could possibly use the CONFIG_CC_NO_ARRAY_BOUNDS thing in a more
targeted way, and disable the warning only for particular uses: again
the s390 case as an example:

  KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_NO_ARRAY_BOUNDS),-Wno-array-bounds)

but this ends up just doing it globally in the top-level Makefile, since
the current issues are spread fairly widely all over:

  KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds

We'll try to limit this later, since the gcc-12 problems are rare enough
that *much* of the kernel can be built with it without disabling this
warning.

Cc: Kees Cook <[email protected]>
Cc: Nathan Chancellor <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: torvalds

Makefile

@@ -788,6 +788,7 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG)      := -fstack-protector-strong
 KBUILD_CFLAGS += $(stackp-flags-y)
 
 KBUILD_CFLAGS-$(CONFIG_WERROR) += -Werror
+KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
 KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
 
 ifdef CONFIG_CC_IS_CLANG

arch/s390/Kconfig

@@ -125,6 +125,7 @@ config S390
 	select CLONE_BACKWARDS2
 	select DMA_OPS if PCI
 	select DYNAMIC_FTRACE if FUNCTION_TRACER
+	select GCC12_NO_ARRAY_BOUNDS
 	select GENERIC_ALLOCATOR
 	select GENERIC_CPU_AUTOPROBE
 	select GENERIC_CPU_VULNERABILITIES

arch/s390/Makefile

@@ -32,15 +32,7 @@ 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
+KBUILD_CFLAGS_DECOMPRESSOR += $(if $(CONFIG_CC_NO_ARRAY_BOUNDS),-Wno-array-bounds)
 
 UTS_MACHINE	:= s390x
 STACK_SIZE	:= $(if $(CONFIG_KASAN),65536,16384)

init/Kconfig

@@ -885,6 +885,15 @@ config CC_IMPLICIT_FALLTHROUGH
 	default "-Wimplicit-fallthrough=5" if CC_IS_GCC && $(cc-option,-Wimplicit-fallthrough=5)
 	default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
 
+# Currently, disable gcc-12 array-bounds globally.
+# We may want to target only particular configurations some day.
+config GCC12_NO_ARRAY_BOUNDS
+	def_bool y
+
+config CC_NO_ARRAY_BOUNDS
+	bool
+	default y if CC_IS_GCC && GCC_VERSION >= 120000 && GCC_VERSION < 130000 && GCC12_NO_ARRAY_BOUNDS
+
 #
 # For architectures that know their GCC __int128 support is sound
 #