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b0630d1845
commitd0afcfeb9eupstream. A new on by default warning in clang [1] aims to flags instances where const variables without static or thread local storage or const members in aggregate types are not initialized because it can lead to an indeterminate value. This is quite noisy for the kernel due to instances originating from header files such as: drivers/gpu/drm/i915/gt/intel_ring.h:62:2: error: default initialization of an object of type 'typeof (ring->size)' (aka 'const unsigned int') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe] 62 | typecheck(typeof(ring->size), next); | ^ include/linux/typecheck.h:10:9: note: expanded from macro 'typecheck' 10 | ({ type __dummy; \ | ^ include/net/ip.h:478:14: error: default initialization of an object of type 'typeof (rt->dst.expires)' (aka 'const unsigned long') leaves the object uninitialized [-Werror,-Wdefault-const-init-var-unsafe] 478 | if (mtu && time_before(jiffies, rt->dst.expires)) | ^ include/linux/jiffies.h:138:26: note: expanded from macro 'time_before' 138 | #define time_before(a,b) time_after(b,a) | ^ include/linux/jiffies.h:128:3: note: expanded from macro 'time_after' 128 | (typecheck(unsigned long, a) && \ | ^ include/linux/typecheck.h:11:12: note: expanded from macro 'typecheck' 11 | typeof(x) __dummy2; \ | ^ include/linux/list.h:409:27: warning: default initialization of an object of type 'union (unnamed union at include/linux/list.h:409:27)' with const member leaves the object uninitialized [-Wdefault-const-init-field-unsafe] 409 | struct list_head *next = smp_load_acquire(&head->next); | ^ include/asm-generic/barrier.h:176:29: note: expanded from macro 'smp_load_acquire' 176 | #define smp_load_acquire(p) __smp_load_acquire(p) | ^ arch/arm64/include/asm/barrier.h:164:59: note: expanded from macro '__smp_load_acquire' 164 | union { __unqual_scalar_typeof(*p) __val; char __c[1]; } __u; \ | ^ include/linux/list.h:409:27: note: member '__val' declared 'const' here crypto/scatterwalk.c:66:22: error: default initialization of an object of type 'struct scatter_walk' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe] 66 | struct scatter_walk walk; | ^ include/crypto/algapi.h:112:15: note: member 'addr' declared 'const' here 112 | void *const addr; | ^ fs/hugetlbfs/inode.c:733:24: error: default initialization of an object of type 'struct vm_area_struct' with const member leaves the object uninitialized [-Werror,-Wdefault-const-init-field-unsafe] 733 | struct vm_area_struct pseudo_vma; | ^ include/linux/mm_types.h:803:20: note: member 'vm_flags' declared 'const' here 803 | const vm_flags_t vm_flags; | ^ Silencing the instances from typecheck.h is difficult because '= {}' is not available in older but supported compilers and '= {0}' would cause warnings about a literal 0 being treated as NULL. While it might be possible to come up with a local hack to silence the warning for clang-21+, it may not be worth it since -Wuninitialized will still trigger if an uninitialized const variable is actually used. In all audited cases of the "field" variant of the warning, the members are either not used in the particular call path, modified through other means such as memset() / memcpy() because the containing object is not const, or are within a union with other non-const members. Since this warning does not appear to have a high signal to noise ratio, just disable it. Cc: stable@vger.kernel.org Link:576161cb60[1] Reported-by: Linux Kernel Functional Testing <lkft@linaro.org> Closes: https://lore.kernel.org/CA+G9fYuNjKcxFKS_MKPRuga32XbndkLGcY-PVuoSwzv6VWbY=w@mail.gmail.com/ Reported-by: Marcus Seyfarth <m.seyfarth@gmail.com> Closes: https://github.com/ClangBuiltLinux/linux/issues/2088 Signed-off-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
235 lines
8.2 KiB
Makefile
235 lines
8.2 KiB
Makefile
# SPDX-License-Identifier: GPL-2.0
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# ==========================================================================
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# make W=... settings
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#
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# There are four warning groups enabled by W=1, W=2, W=3, and W=e
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# They are independent, and can be combined like W=12 or W=123e.
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# ==========================================================================
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# Default set of warnings, always enabled
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KBUILD_CFLAGS += -Wall
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KBUILD_CFLAGS += -Wundef
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KBUILD_CFLAGS += -Werror=implicit-function-declaration
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KBUILD_CFLAGS += -Werror=implicit-int
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KBUILD_CFLAGS += -Werror=return-type
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KBUILD_CFLAGS += -Werror=strict-prototypes
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KBUILD_CFLAGS += -Wno-format-security
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KBUILD_CFLAGS += -Wno-trigraphs
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KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,)
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KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
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ifneq ($(CONFIG_FRAME_WARN),0)
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KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
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endif
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KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror
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KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y)
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KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
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ifdef CONFIG_CC_IS_CLANG
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# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable.
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KBUILD_CFLAGS += -Wno-gnu
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# Clang may emit a warning when a const variable, such as the dummy variables
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# in typecheck(), or const member of an aggregate type are not initialized,
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# which can result in unexpected behavior. However, in many audited cases of
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# the "field" variant of the warning, this is intentional because the field is
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# never used within a particular call path, the field is within a union with
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# other non-const members, or the containing object is not const so the field
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# can be modified via memcpy() / memset(). While the variable warning also gets
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# disabled with this same switch, there should not be too much coverage lost
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# because -Wuninitialized will still flag when an uninitialized const variable
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# is used.
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KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe)
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else
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# gcc inanely warns about local variables called 'main'
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KBUILD_CFLAGS += -Wno-main
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endif
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# These warnings generated too much noise in a regular build.
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# Use make W=1 to enable them (see scripts/Makefile.extrawarn)
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KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
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KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
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# These result in bogus false positives
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KBUILD_CFLAGS += $(call cc-disable-warning, dangling-pointer)
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# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
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KBUILD_CFLAGS += -Wvla
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# disable pointer signed / unsigned warnings in gcc 4.0
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KBUILD_CFLAGS += -Wno-pointer-sign
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# In order to make sure new function cast mismatches are not introduced
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# in the kernel (to avoid tripping CFI checking), the kernel should be
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# globally built with -Wcast-function-type.
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KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)
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# The allocators already balk at large sizes, so silence the compiler
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# warnings for bounds checks involving those possible values. While
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# -Wno-alloc-size-larger-than would normally be used here, earlier versions
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# of gcc (<9.1) weirdly don't handle the option correctly when _other_
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# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX
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# doesn't work (as it is documented to), silently resolving to "0" prior to
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# version 9.1 (and producing an error more recently). Numeric values larger
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# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently
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# ignored, continuing to default to PTRDIFF_MAX. So, left with no other
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# choice, we must perform a versioned check to disable this warning.
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# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au
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KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than
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KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
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# Prohibit date/time macros, which would make the build non-deterministic
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KBUILD_CFLAGS += -Werror=date-time
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# enforce correct pointer usage
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KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types)
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# Require designated initializers for all marked structures
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KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
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# Warn if there is an enum types mismatch
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KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
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# backward compatibility
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KBUILD_EXTRA_WARN ?= $(KBUILD_ENABLE_EXTRA_GCC_CHECKS)
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ifeq ("$(origin W)", "command line")
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KBUILD_EXTRA_WARN := $(W)
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endif
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export KBUILD_EXTRA_WARN
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#
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# W=1 - warnings which may be relevant and do not occur too often
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#
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ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
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KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter
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KBUILD_CFLAGS += -Wmissing-declarations
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KBUILD_CFLAGS += $(call cc-option, -Wrestrict)
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KBUILD_CFLAGS += -Wmissing-format-attribute
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KBUILD_CFLAGS += -Wmissing-prototypes
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KBUILD_CFLAGS += -Wold-style-definition
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KBUILD_CFLAGS += -Wmissing-include-dirs
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KBUILD_CFLAGS += $(call cc-option, -Wunused-but-set-variable)
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KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)
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KBUILD_CFLAGS += $(call cc-option, -Wpacked-not-aligned)
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KBUILD_CFLAGS += $(call cc-option, -Wformat-overflow)
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KBUILD_CFLAGS += $(call cc-option, -Wformat-truncation)
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KBUILD_CFLAGS += $(call cc-option, -Wstringop-overflow)
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KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation)
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KBUILD_CPPFLAGS += -Wundef
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KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
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else
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# Some diagnostics enabled by default are noisy.
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# Suppress them by using -Wno... except for W=1.
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KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
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KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
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KBUILD_CFLAGS += $(call cc-disable-warning, restrict)
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KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
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KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
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KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
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KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow)
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KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
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ifdef CONFIG_CC_IS_CLANG
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# Clang before clang-16 would warn on default argument promotions.
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ifneq ($(call clang-min-version, 160000),y)
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# Disable -Wformat
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KBUILD_CFLAGS += -Wno-format
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# Then re-enable flags that were part of the -Wformat group that aren't
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# problematic.
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KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier
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KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull
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# Requires clang-12+.
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ifeq ($(call clang-min-version, 120000),y)
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KBUILD_CFLAGS += -Wformat-insufficient-args
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endif
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endif
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KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
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KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
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KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
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KBUILD_CFLAGS += $(call cc-disable-warning, cast-function-type-strict)
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KBUILD_CFLAGS += -Wno-enum-compare-conditional
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endif
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endif
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#
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# W=2 - warnings which occur quite often but may still be relevant
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#
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ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
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KBUILD_CFLAGS += -Wdisabled-optimization
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KBUILD_CFLAGS += -Wshadow
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KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
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KBUILD_CFLAGS += -Wmissing-field-initializers
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KBUILD_CFLAGS += -Wtype-limits
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KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized)
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KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
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ifdef CONFIG_CC_IS_CLANG
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KBUILD_CFLAGS += -Winitializer-overrides
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endif
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KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2
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else
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# The following turn off the warnings enabled by -Wextra
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KBUILD_CFLAGS += -Wno-missing-field-initializers
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KBUILD_CFLAGS += -Wno-type-limits
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KBUILD_CFLAGS += -Wno-shift-negative-value
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ifdef CONFIG_CC_IS_CLANG
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KBUILD_CFLAGS += -Wno-enum-enum-conversion
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endif
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ifdef CONFIG_CC_IS_CLANG
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KBUILD_CFLAGS += -Wno-initializer-overrides
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else
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KBUILD_CFLAGS += -Wno-maybe-uninitialized
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endif
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endif
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#
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# W=3 - more obscure warnings, can most likely be ignored
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#
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ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),)
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KBUILD_CFLAGS += -Wbad-function-cast
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KBUILD_CFLAGS += -Wcast-align
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KBUILD_CFLAGS += -Wcast-qual
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KBUILD_CFLAGS += -Wconversion
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KBUILD_CFLAGS += -Wpacked
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KBUILD_CFLAGS += -Wpadded
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KBUILD_CFLAGS += -Wpointer-arith
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KBUILD_CFLAGS += -Wredundant-decls
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KBUILD_CFLAGS += -Wsign-compare
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KBUILD_CFLAGS += -Wswitch-default
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KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat)
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KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3
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else
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# The following turn off the warnings enabled by -Wextra
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KBUILD_CFLAGS += -Wno-sign-compare
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endif
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#
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# W=e - error out on warnings
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#
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ifneq ($(findstring e, $(KBUILD_EXTRA_WARN)),)
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KBUILD_CFLAGS += -Werror
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endif
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