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=$(CONFIG_FRAME_WARN) 26endif 27 28KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror 29KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y) 30KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds 31 32ifdef CONFIG_CC_IS_CLANG 33# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable. 34KBUILD_CFLAGS += -Wno-gnu 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# These result in bogus false positives 59KBUILD_CFLAGS += $(call cc-option, -Wno-dangling-pointer) 60 61# Stack Variable Length Arrays (VLAs) must not be used in the kernel. 62# Function array parameters should, however, be usable, but -Wvla will 63# warn for those. Clang has no way yet to distinguish between the VLA 64# types, so depend on GCC for now to keep stack VLAs out of the tree. 65# https://github.com/llvm/llvm-project/issues/57098 66# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98217 67KBUILD_CFLAGS += $(call cc-option,-Wvla-larger-than=1) 68 69# disable pointer signed / unsigned warnings in gcc 4.0 70KBUILD_CFLAGS += -Wno-pointer-sign 71 72# In order to make sure new function cast mismatches are not introduced 73# in the kernel (to avoid tripping CFI checking), the kernel should be 74# globally built with -Wcast-function-type. 75KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type) 76 77# Currently, disable -Wstringop-overflow for GCC 11, globally. 78KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-option, -Wno-stringop-overflow) 79KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow) 80 81# Currently, disable -Wunterminated-string-initialization as broken 82KBUILD_CFLAGS += $(call cc-option, -Wno-unterminated-string-initialization) 83 84# The allocators already balk at large sizes, so silence the compiler 85# warnings for bounds checks involving those possible values. While 86# -Wno-alloc-size-larger-than would normally be used here, earlier versions 87# of gcc (<9.1) weirdly don't handle the option correctly when _other_ 88# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX 89# doesn't work (as it is documented to), silently resolving to "0" prior to 90# version 9.1 (and producing an error more recently). Numeric values larger 91# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently 92# ignored, continuing to default to PTRDIFF_MAX. So, left with no other 93# choice, we must perform a versioned check to disable this warning. 94# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au 95KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than 96KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) 97 98# Prohibit date/time macros, which would make the build non-deterministic 99KBUILD_CFLAGS += -Werror=date-time 100 101# enforce correct pointer usage 102KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types) 103 104# Require designated initializers for all marked structures 105KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) 106 107# Warn if there is an enum types mismatch 108KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion) 109 110KBUILD_CFLAGS += -Wunused 111 112# 113# W=1 - warnings which may be relevant and do not occur too often 114# 115ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),) 116 117KBUILD_CFLAGS += -Wmissing-format-attribute 118KBUILD_CFLAGS += -Wmissing-include-dirs 119KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable) 120 121KBUILD_CPPFLAGS += -Wundef 122KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 123 124else 125 126# Some diagnostics enabled by default are noisy. 127# Suppress them by using -Wno... except for W=1. 128KBUILD_CFLAGS += $(call cc-option, -Wno-unused-but-set-variable) 129KBUILD_CFLAGS += $(call cc-option, -Wno-unused-const-variable) 130KBUILD_CFLAGS += $(call cc-option, -Wno-packed-not-aligned) 131KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow) 132ifdef CONFIG_CC_IS_GCC 133KBUILD_CFLAGS += $(call cc-option, -Wno-format-truncation) 134endif 135KBUILD_CFLAGS += $(call cc-option, -Wno-stringop-truncation) 136 137KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang 138 139ifdef CONFIG_CC_IS_CLANG 140# Clang before clang-16 would warn on default argument promotions. 141ifneq ($(call clang-min-version, 160000),y) 142# Disable -Wformat 143KBUILD_CFLAGS += -Wno-format 144# Then re-enable flags that were part of the -Wformat group that aren't 145# problematic. 146KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier 147KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull 148# Requires clang-12+. 149ifeq ($(call clang-min-version, 120000),y) 150KBUILD_CFLAGS += -Wformat-insufficient-args 151endif 152endif 153KBUILD_CFLAGS += $(call cc-option, -Wno-pointer-to-enum-cast) 154KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare 155KBUILD_CFLAGS += $(call cc-option, -Wno-unaligned-access) 156KBUILD_CFLAGS += -Wno-enum-compare-conditional 157endif 158 159endif 160 161# 162# W=2 - warnings which occur quite often but may still be relevant 163# 164ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),) 165 166KBUILD_CFLAGS += -Wdisabled-optimization 167KBUILD_CFLAGS += -Wshadow 168KBUILD_CFLAGS += $(call cc-option, -Wlogical-op) 169KBUILD_CFLAGS += $(call cc-option, -Wunused-macros) 170 171KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2 172 173else 174 175# The following turn off the warnings enabled by -Wextra 176KBUILD_CFLAGS += -Wno-missing-field-initializers 177KBUILD_CFLAGS += -Wno-type-limits 178KBUILD_CFLAGS += -Wno-shift-negative-value 179 180ifdef CONFIG_CC_IS_CLANG 181KBUILD_CFLAGS += -Wno-enum-enum-conversion 182endif 183 184ifdef CONFIG_CC_IS_GCC 185KBUILD_CFLAGS += -Wno-maybe-uninitialized 186endif 187 188endif 189 190# 191# W=3 - more obscure warnings, can most likely be ignored 192# 193ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),) 194 195KBUILD_CFLAGS += -Wbad-function-cast 196KBUILD_CFLAGS += -Wcast-align 197KBUILD_CFLAGS += -Wcast-qual 198KBUILD_CFLAGS += -Wconversion 199KBUILD_CFLAGS += -Wpacked 200KBUILD_CFLAGS += -Wpadded 201KBUILD_CFLAGS += -Wpointer-arith 202KBUILD_CFLAGS += -Wredundant-decls 203KBUILD_CFLAGS += -Wsign-compare 204KBUILD_CFLAGS += -Wswitch-default 205 206KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3 207 208else 209 210# The following turn off the warnings enabled by -Wextra 211KBUILD_CFLAGS += -Wno-sign-compare 212KBUILD_CFLAGS += -Wno-unused-parameter 213 214endif 215 216# 217# W=e - error out on warnings 218# 219ifneq ($(findstring e, $(KBUILD_EXTRA_WARN)),) 220 221KBUILD_CFLAGS += -Werror 222 223endif 224