xref: /scripts/Makefile.extrawarn

# SPDX-License-Identifier: GPL-2.0
# ==========================================================================
# make W=... settings
#
# There are four warning groups enabled by W=1, W=2, W=3, and W=e
# They are independent, and can be combined like W=12 or W=123e.
# ==========================================================================

# Default set of warnings, always enabled
KBUILD_CFLAGS += -Wall
KBUILD_CFLAGS += -Wextra
KBUILD_CFLAGS += -Wundef
KBUILD_CFLAGS += -Werror=implicit-function-declaration
KBUILD_CFLAGS += -Werror=implicit-int
KBUILD_CFLAGS += -Werror=return-type
KBUILD_CFLAGS += -Werror=strict-prototypes
KBUILD_CFLAGS += -Wno-format-security
KBUILD_CFLAGS += -Wno-trigraphs
KBUILD_CFLAGS += $(call cc-disable-warning, frame-address)
KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)

ifneq ($(CONFIG_FRAME_WARN),0)
KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
endif

KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror
KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y)
KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds

ifdef CONFIG_CC_IS_CLANG
# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable.
KBUILD_CFLAGS += -Wno-gnu

# Clang checks for overflow/truncation with '%p', while GCC does not:
# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)

# Clang may emit a warning when a const variable, such as the dummy variables
# in typecheck(), or const member of an aggregate type are not initialized,
# which can result in unexpected behavior. However, in many audited cases of
# the "field" variant of the warning, this is intentional because the field is
# never used within a particular call path, the field is within a union with
# other non-const members, or the containing object is not const so the field
# can be modified via memcpy() / memset(). While the variable warning also gets
# disabled with this same switch, there should not be too much coverage lost
# because -Wuninitialized will still flag when an uninitialized const variable
# is used.
KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe)
else

# gcc inanely warns about local variables called 'main'
KBUILD_CFLAGS += -Wno-main
endif

# These result in bogus false positives
KBUILD_CFLAGS += $(call cc-disable-warning, dangling-pointer)

# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
KBUILD_CFLAGS += -Wvla

# disable pointer signed / unsigned warnings in gcc 4.0
KBUILD_CFLAGS += -Wno-pointer-sign

# In order to make sure new function cast mismatches are not introduced
# in the kernel (to avoid tripping CFI checking), the kernel should be
# globally built with -Wcast-function-type.
KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)

# Currently, disable -Wstringop-overflow for GCC 11, globally.
KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-disable-warning, stringop-overflow)
KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow)

# Currently, disable -Wunterminated-string-initialization as broken
KBUILD_CFLAGS += $(call cc-disable-warning, unterminated-string-initialization)

# The allocators already balk at large sizes, so silence the compiler
# warnings for bounds checks involving those possible values. While
# -Wno-alloc-size-larger-than would normally be used here, earlier versions
# of gcc (<9.1) weirdly don't handle the option correctly when _other_
# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX
# doesn't work (as it is documented to), silently resolving to "0" prior to
# version 9.1 (and producing an error more recently). Numeric values larger
# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently
# ignored, continuing to default to PTRDIFF_MAX. So, left with no other
# choice, we must perform a versioned check to disable this warning.
# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au
KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than
KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)

# Prohibit date/time macros, which would make the build non-deterministic
KBUILD_CFLAGS += -Werror=date-time

# enforce correct pointer usage
KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types)

# Require designated initializers for all marked structures
KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)

# Warn if there is an enum types mismatch
KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)

# Explicitly clear padding bits during variable initialization
KBUILD_CFLAGS += $(call cc-option,-fzero-init-padding-bits=all)

KBUILD_CFLAGS += -Wunused

#
# W=1 - warnings which may be relevant and do not occur too often
#
ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)

KBUILD_CFLAGS += -Wmissing-declarations
KBUILD_CFLAGS += -Wmissing-format-attribute
KBUILD_CFLAGS += -Wmissing-prototypes
KBUILD_CFLAGS += -Wmissing-include-dirs
KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)

KBUILD_CPPFLAGS += -Wundef
KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1

else

# Some diagnostics enabled by default are noisy.
# Suppress them by using -Wno... except for W=1.
KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
ifdef CONFIG_CC_IS_GCC
KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
endif
KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)

KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang

ifdef CONFIG_CC_IS_CLANG
# Clang before clang-16 would warn on default argument promotions.
ifneq ($(call clang-min-version, 160000),y)
# Disable -Wformat
KBUILD_CFLAGS += -Wno-format
# Then re-enable flags that were part of the -Wformat group that aren't
# problematic.
KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier
KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull
# Requires clang-12+.
ifeq ($(call clang-min-version, 120000),y)
KBUILD_CFLAGS += -Wformat-insufficient-args
endif
endif
KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
KBUILD_CFLAGS += -Wno-enum-compare-conditional
endif

endif

#
# W=2 - warnings which occur quite often but may still be relevant
#
ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)

KBUILD_CFLAGS += -Wdisabled-optimization
KBUILD_CFLAGS += -Wshadow
KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)

KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2

else

# The following turn off the warnings enabled by -Wextra
KBUILD_CFLAGS += -Wno-missing-field-initializers
KBUILD_CFLAGS += -Wno-type-limits
KBUILD_CFLAGS += -Wno-shift-negative-value

ifdef CONFIG_CC_IS_CLANG
KBUILD_CFLAGS += -Wno-enum-enum-conversion
endif

ifdef CONFIG_CC_IS_GCC
KBUILD_CFLAGS += -Wno-maybe-uninitialized
endif

endif

#
# W=3 - more obscure warnings, can most likely be ignored
#
ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),)

KBUILD_CFLAGS += -Wbad-function-cast
KBUILD_CFLAGS += -Wcast-align
KBUILD_CFLAGS += -Wcast-qual
KBUILD_CFLAGS += -Wconversion
KBUILD_CFLAGS += -Wpacked
KBUILD_CFLAGS += -Wpadded
KBUILD_CFLAGS += -Wpointer-arith
KBUILD_CFLAGS += -Wredundant-decls
KBUILD_CFLAGS += -Wsign-compare
KBUILD_CFLAGS += -Wswitch-default

KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3

else

# The following turn off the warnings enabled by -Wextra
KBUILD_CFLAGS += -Wno-sign-compare
KBUILD_CFLAGS += -Wno-unused-parameter

endif

#
# W=e - error out on warnings
#
ifneq ($(findstring e, $(KBUILD_EXTRA_WARN)),)

KBUILD_CFLAGS += -Werror

endif