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 += -Wextra 12KBUILD_CFLAGS += -Wundef 13KBUILD_CFLAGS += -Werror=implicit-function-declaration 14KBUILD_CFLAGS += -Werror=implicit-int 15KBUILD_CFLAGS += -Werror=return-type 16KBUILD_CFLAGS += -Werror=strict-prototypes 17KBUILD_CFLAGS += -Wno-format-security 18KBUILD_CFLAGS += -Wno-trigraphs 19KBUILD_CFLAGS += $(call cc-option, -Wno-frame-address) 20KBUILD_CFLAGS += $(call cc-option, -Wno-address-of-packed-member) 21KBUILD_CFLAGS += -Wmissing-declarations 22KBUILD_CFLAGS += -Wmissing-prototypes 23 24ifneq ($(CONFIG_FRAME_WARN),0) 25KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN) 26endif 27 28KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds 29 30ifdef CONFIG_CC_IS_CLANG 31# The kernel builds with '-std=gnu11' and '-fms-extensions' so use of GNU and 32# Microsoft extensions is acceptable. 33KBUILD_CFLAGS += -Wno-gnu 34KBUILD_CFLAGS += -Wno-microsoft-anon-tag 35 36# Clang checks for overflow/truncation with '%p', while GCC does not: 37# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219 38KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow-non-kprintf) 39KBUILD_CFLAGS += $(call cc-option, -Wno-format-truncation-non-kprintf) 40 41# Clang may emit a warning when a const variable, such as the dummy variables 42# in typecheck(), or const member of an aggregate type are not initialized, 43# which can result in unexpected behavior. However, in many audited cases of 44# the "field" variant of the warning, this is intentional because the field is 45# never used within a particular call path, the field is within a union with 46# other non-const members, or the containing object is not const so the field 47# can be modified via memcpy() / memset(). While the variable warning also gets 48# disabled with this same switch, there should not be too much coverage lost 49# because -Wuninitialized will still flag when an uninitialized const variable 50# is used. 51KBUILD_CFLAGS += $(call cc-option, -Wno-default-const-init-unsafe) 52else 53 54# gcc inanely warns about local variables called 'main' 55KBUILD_CFLAGS += -Wno-main 56endif 57 58# Too noisy on range checks and in macros handling both signed and unsigned. 59KBUILD_CFLAGS += -Wno-type-limits 60 61# These result in bogus false positives 62KBUILD_CFLAGS += $(call cc-option, -Wno-dangling-pointer) 63 64# Stack Variable Length Arrays (VLAs) must not be used in the kernel. 65# Function array parameters should, however, be usable, but -Wvla will 66# warn for those. Clang has no way yet to distinguish between the VLA 67# types, so depend on GCC for now to keep stack VLAs out of the tree. 68# https://github.com/llvm/llvm-project/issues/57098 69# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98217 70KBUILD_CFLAGS += $(call cc-option,-Wvla-larger-than=1) 71 72# disable pointer signed / unsigned warnings in gcc 4.0 73KBUILD_CFLAGS += -Wno-pointer-sign 74 75# In order to make sure new function cast mismatches are not introduced 76# in the kernel (to avoid tripping CFI checking), the kernel should be 77# globally built with -Wcast-function-type. 78KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type) 79 80# Currently, disable -Wstringop-overflow for GCC 11, globally. 81KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-option, -Wno-stringop-overflow) 82KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow) 83 84# Currently, disable -Wunterminated-string-initialization as broken 85KBUILD_CFLAGS += $(call cc-option, -Wno-unterminated-string-initialization) 86 87# The allocators already balk at large sizes, so silence the compiler 88# warnings for bounds checks involving those possible values. While 89# -Wno-alloc-size-larger-than would normally be used here, earlier versions 90# of gcc (<9.1) weirdly don't handle the option correctly when _other_ 91# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX 92# doesn't work (as it is documented to), silently resolving to "0" prior to 93# version 9.1 (and producing an error more recently). Numeric values larger 94# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently 95# ignored, continuing to default to PTRDIFF_MAX. So, left with no other 96# choice, we must perform a versioned check to disable this warning. 97# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au 98KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than 99KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) 100 101# Prohibit date/time macros, which would make the build non-deterministic 102KBUILD_CFLAGS += -Werror=date-time 103 104# enforce correct pointer usage 105KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types) 106 107# Require designated initializers for all marked structures 108KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) 109 110# Warn if there is an enum types mismatch 111KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion) 112 113KBUILD_CFLAGS += -Wunused 114 115# 116# W=1 - warnings which may be relevant and do not occur too often 117# 118ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),) 119 120KBUILD_CFLAGS += -Wmissing-format-attribute 121KBUILD_CFLAGS += -Wmissing-include-dirs 122KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable) 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-option, -Wno-unused-but-set-variable) 132KBUILD_CFLAGS += $(call cc-option, -Wno-unused-const-variable) 133KBUILD_CFLAGS += $(call cc-option, -Wno-packed-not-aligned) 134KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow) 135ifdef CONFIG_CC_IS_GCC 136KBUILD_CFLAGS += $(call cc-option, -Wno-format-truncation) 137endif 138KBUILD_CFLAGS += $(call cc-option, -Wno-stringop-truncation) 139 140KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang 141 142ifdef CONFIG_CC_IS_CLANG 143# Clang before clang-16 would warn on default argument promotions. 144ifneq ($(call clang-min-version, 160000),y) 145# Disable -Wformat 146KBUILD_CFLAGS += -Wno-format 147# Then re-enable flags that were part of the -Wformat group that aren't 148# problematic. 149KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier 150KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull 151# Requires clang-12+. 152ifeq ($(call clang-min-version, 120000),y) 153KBUILD_CFLAGS += -Wformat-insufficient-args 154endif 155endif 156KBUILD_CFLAGS += $(call cc-option, -Wno-pointer-to-enum-cast) 157KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare 158KBUILD_CFLAGS += $(call cc-option, -Wno-unaligned-access) 159KBUILD_CFLAGS += -Wno-enum-compare-conditional 160endif 161 162endif 163 164# 165# W=2 - warnings which occur quite often but may still be relevant 166# 167ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),) 168 169KBUILD_CFLAGS += -Wdisabled-optimization 170KBUILD_CFLAGS += -Wshadow 171KBUILD_CFLAGS += $(call cc-option, -Wlogical-op) 172KBUILD_CFLAGS += $(call cc-option, -Wunused-macros) 173 174KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2 175 176else 177 178# The following turn off the warnings enabled by -Wextra 179KBUILD_CFLAGS += -Wno-missing-field-initializers 180KBUILD_CFLAGS += -Wno-shift-negative-value 181 182ifdef CONFIG_CC_IS_CLANG 183KBUILD_CFLAGS += -Wno-enum-enum-conversion 184endif 185 186ifdef CONFIG_CC_IS_GCC 187KBUILD_CFLAGS += -Wno-maybe-uninitialized 188endif 189 190endif 191 192# 193# W=3 - more obscure warnings, can most likely be ignored 194# 195ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),) 196 197KBUILD_CFLAGS += -Wbad-function-cast 198KBUILD_CFLAGS += -Wcast-align 199KBUILD_CFLAGS += -Wcast-qual 200KBUILD_CFLAGS += -Wconversion 201KBUILD_CFLAGS += -Wpacked 202KBUILD_CFLAGS += -Wpadded 203KBUILD_CFLAGS += -Wpointer-arith 204KBUILD_CFLAGS += -Wredundant-decls 205KBUILD_CFLAGS += -Wsign-compare 206KBUILD_CFLAGS += -Wswitch-default 207 208KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3 209 210else 211 212# The following turn off the warnings enabled by -Wextra 213KBUILD_CFLAGS += -Wno-sign-compare 214KBUILD_CFLAGS += -Wno-unused-parameter 215 216endif 217 218# 219# W=e and CONFIG_WERROR - error out on warnings 220# 221ifneq ($(findstring e, $(KBUILD_EXTRA_WARN))$(CONFIG_WERROR),) 222 223KBUILD_CPPFLAGS += -Werror 224KBUILD_AFLAGS += -Wa,--fatal-warnings 225KBUILD_LDFLAGS += --fatal-warnings 226KBUILD_USERCFLAGS += -Werror 227KBUILD_USERLDFLAGS += -Wl,--fatal-warnings 228KBUILD_RUSTFLAGS += -Dwarnings 229 230# While hostprog flags are used during build bootstrapping (thus should not 231# depend on CONFIG_ symbols), -Werror is disruptive and should be opted into. 232# Only apply -Werror to hostprogs built after the initial Kconfig stage. 233KBUILD_HOSTCFLAGS += -Werror 234KBUILD_HOSTLDFLAGS += -Wl,--fatal-warnings 235KBUILD_HOSTRUSTFLAGS += -Dwarnings 236 237endif 238