1# SPDX-License-Identifier: GPL-2.0 2# ========================================================================== 3# make W=... settings 4# 5# There are four warning groups enabled by W=1, W=2, W=3, and W=e 6# They are independent, and can be combined like W=12 or W=123e. 7# ========================================================================== 8 9# Default set of warnings, always enabled 10KBUILD_CFLAGS += -Wall 11KBUILD_CFLAGS += -Wundef 12KBUILD_CFLAGS += -Werror=implicit-function-declaration 13KBUILD_CFLAGS += -Werror=implicit-int 14KBUILD_CFLAGS += -Werror=return-type 15KBUILD_CFLAGS += -Werror=strict-prototypes 16KBUILD_CFLAGS += -Wno-format-security 17KBUILD_CFLAGS += -Wno-trigraphs 18KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,) 19KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member) 20 21ifneq ($(CONFIG_FRAME_WARN),0) 22KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN) 23endif 24 25KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror 26KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y) 27KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds 28 29ifdef CONFIG_CC_IS_CLANG 30# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable. 31KBUILD_CFLAGS += -Wno-gnu 32 33# Clang may emit a warning when a const variable, such as the dummy variables 34# in typecheck(), or const member of an aggregate type are not initialized, 35# which can result in unexpected behavior. However, in many audited cases of 36# the "field" variant of the warning, this is intentional because the field is 37# never used within a particular call path, the field is within a union with 38# other non-const members, or the containing object is not const so the field 39# can be modified via memcpy() / memset(). While the variable warning also gets 40# disabled with this same switch, there should not be too much coverage lost 41# because -Wuninitialized will still flag when an uninitialized const variable 42# is used. 43KBUILD_CFLAGS += $(call cc-disable-warning, default-const-init-unsafe) 44else 45 46# gcc inanely warns about local variables called 'main' 47KBUILD_CFLAGS += -Wno-main 48endif 49 50# These warnings generated too much noise in a regular build. 51# Use make W=1 to enable them (see scripts/Makefile.extrawarn) 52KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) 53KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable) 54 55# These result in bogus false positives 56KBUILD_CFLAGS += $(call cc-disable-warning, dangling-pointer) 57 58# Variable Length Arrays (VLAs) should not be used anywhere in the kernel 59KBUILD_CFLAGS += -Wvla 60 61# disable pointer signed / unsigned warnings in gcc 4.0 62KBUILD_CFLAGS += -Wno-pointer-sign 63 64# In order to make sure new function cast mismatches are not introduced 65# in the kernel (to avoid tripping CFI checking), the kernel should be 66# globally built with -Wcast-function-type. 67KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type) 68 69# The allocators already balk at large sizes, so silence the compiler 70# warnings for bounds checks involving those possible values. While 71# -Wno-alloc-size-larger-than would normally be used here, earlier versions 72# of gcc (<9.1) weirdly don't handle the option correctly when _other_ 73# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX 74# doesn't work (as it is documented to), silently resolving to "0" prior to 75# version 9.1 (and producing an error more recently). Numeric values larger 76# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently 77# ignored, continuing to default to PTRDIFF_MAX. So, left with no other 78# choice, we must perform a versioned check to disable this warning. 79# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au 80KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than 81KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) 82 83# Prohibit date/time macros, which would make the build non-deterministic 84KBUILD_CFLAGS += -Werror=date-time 85 86# enforce correct pointer usage 87KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types) 88 89# Require designated initializers for all marked structures 90KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) 91 92# Warn if there is an enum types mismatch 93KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion) 94 95# backward compatibility 96KBUILD_EXTRA_WARN ?= $(KBUILD_ENABLE_EXTRA_GCC_CHECKS) 97 98ifeq ("$(origin W)", "command line") 99 KBUILD_EXTRA_WARN := $(W) 100endif 101 102export KBUILD_EXTRA_WARN 103 104# 105# W=1 - warnings which may be relevant and do not occur too often 106# 107ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),) 108 109KBUILD_CFLAGS += -Wextra -Wunused -Wno-unused-parameter 110KBUILD_CFLAGS += -Wmissing-declarations 111KBUILD_CFLAGS += $(call cc-option, -Wrestrict) 112KBUILD_CFLAGS += -Wmissing-format-attribute 113KBUILD_CFLAGS += -Wmissing-prototypes 114KBUILD_CFLAGS += -Wold-style-definition 115KBUILD_CFLAGS += -Wmissing-include-dirs 116KBUILD_CFLAGS += $(call cc-option, -Wunused-but-set-variable) 117KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable) 118KBUILD_CFLAGS += $(call cc-option, -Wpacked-not-aligned) 119KBUILD_CFLAGS += $(call cc-option, -Wformat-overflow) 120KBUILD_CFLAGS += $(call cc-option, -Wformat-truncation) 121KBUILD_CFLAGS += $(call cc-option, -Wstringop-overflow) 122KBUILD_CFLAGS += $(call cc-option, -Wstringop-truncation) 123 124KBUILD_CPPFLAGS += -Wundef 125KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 126 127else 128 129# Some diagnostics enabled by default are noisy. 130# Suppress them by using -Wno... except for W=1. 131KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable) 132KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable) 133KBUILD_CFLAGS += $(call cc-disable-warning, restrict) 134KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned) 135KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow) 136KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation) 137KBUILD_CFLAGS += $(call cc-disable-warning, stringop-overflow) 138KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation) 139 140ifdef CONFIG_CC_IS_CLANG 141# Clang before clang-16 would warn on default argument promotions. 142ifneq ($(call clang-min-version, 160000),y) 143# Disable -Wformat 144KBUILD_CFLAGS += -Wno-format 145# Then re-enable flags that were part of the -Wformat group that aren't 146# problematic. 147KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier 148KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull 149# Requires clang-12+. 150ifeq ($(call clang-min-version, 120000),y) 151KBUILD_CFLAGS += -Wformat-insufficient-args 152endif 153endif 154KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast) 155KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare 156KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access) 157KBUILD_CFLAGS += $(call cc-disable-warning, cast-function-type-strict) 158KBUILD_CFLAGS += -Wno-enum-compare-conditional 159endif 160 161endif 162 163# 164# W=2 - warnings which occur quite often but may still be relevant 165# 166ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),) 167 168KBUILD_CFLAGS += -Wdisabled-optimization 169KBUILD_CFLAGS += -Wshadow 170KBUILD_CFLAGS += $(call cc-option, -Wlogical-op) 171KBUILD_CFLAGS += -Wmissing-field-initializers 172KBUILD_CFLAGS += -Wtype-limits 173KBUILD_CFLAGS += $(call cc-option, -Wmaybe-uninitialized) 174KBUILD_CFLAGS += $(call cc-option, -Wunused-macros) 175 176ifdef CONFIG_CC_IS_CLANG 177KBUILD_CFLAGS += -Winitializer-overrides 178endif 179 180KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2 181 182else 183 184# The following turn off the warnings enabled by -Wextra 185KBUILD_CFLAGS += -Wno-missing-field-initializers 186KBUILD_CFLAGS += -Wno-type-limits 187KBUILD_CFLAGS += -Wno-shift-negative-value 188 189ifdef CONFIG_CC_IS_CLANG 190KBUILD_CFLAGS += -Wno-enum-enum-conversion 191endif 192 193ifdef CONFIG_CC_IS_CLANG 194KBUILD_CFLAGS += -Wno-initializer-overrides 195else 196KBUILD_CFLAGS += -Wno-maybe-uninitialized 197endif 198 199endif 200 201# 202# W=3 - more obscure warnings, can most likely be ignored 203# 204ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),) 205 206KBUILD_CFLAGS += -Wbad-function-cast 207KBUILD_CFLAGS += -Wcast-align 208KBUILD_CFLAGS += -Wcast-qual 209KBUILD_CFLAGS += -Wconversion 210KBUILD_CFLAGS += -Wpacked 211KBUILD_CFLAGS += -Wpadded 212KBUILD_CFLAGS += -Wpointer-arith 213KBUILD_CFLAGS += -Wredundant-decls 214KBUILD_CFLAGS += -Wsign-compare 215KBUILD_CFLAGS += -Wswitch-default 216KBUILD_CFLAGS += $(call cc-option, -Wpacked-bitfield-compat) 217 218KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3 219 220else 221 222# The following turn off the warnings enabled by -Wextra 223KBUILD_CFLAGS += -Wno-sign-compare 224 225endif 226 227# 228# W=e - error out on warnings 229# 230ifneq ($(findstring e, $(KBUILD_EXTRA_WARN)),) 231 232KBUILD_CFLAGS += -Werror 233 234endif 235