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' so use of GNU extensions is acceptable. 32KBUILD_CFLAGS += -Wno-gnu 33 34# Clang checks for overflow/truncation with '%p', while GCC does not: 35# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219 36KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow-non-kprintf) 37KBUILD_CFLAGS += $(call cc-option, -Wno-format-truncation-non-kprintf) 38 39# Clang may emit a warning when a const variable, such as the dummy variables 40# in typecheck(), or const member of an aggregate type are not initialized, 41# which can result in unexpected behavior. However, in many audited cases of 42# the "field" variant of the warning, this is intentional because the field is 43# never used within a particular call path, the field is within a union with 44# other non-const members, or the containing object is not const so the field 45# can be modified via memcpy() / memset(). While the variable warning also gets 46# disabled with this same switch, there should not be too much coverage lost 47# because -Wuninitialized will still flag when an uninitialized const variable 48# is used. 49KBUILD_CFLAGS += $(call cc-option, -Wno-default-const-init-unsafe) 50else 51 52# gcc inanely warns about local variables called 'main' 53KBUILD_CFLAGS += -Wno-main 54endif 55 56# These result in bogus false positives 57KBUILD_CFLAGS += $(call cc-option, -Wno-dangling-pointer) 58 59# Stack Variable Length Arrays (VLAs) must not be used in the kernel. 60# Function array parameters should, however, be usable, but -Wvla will 61# warn for those. Clang has no way yet to distinguish between the VLA 62# types, so depend on GCC for now to keep stack VLAs out of the tree. 63# https://github.com/llvm/llvm-project/issues/57098 64# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98217 65KBUILD_CFLAGS += $(call cc-option,-Wvla-larger-than=1) 66 67# disable pointer signed / unsigned warnings in gcc 4.0 68KBUILD_CFLAGS += -Wno-pointer-sign 69 70# In order to make sure new function cast mismatches are not introduced 71# in the kernel (to avoid tripping CFI checking), the kernel should be 72# globally built with -Wcast-function-type. 73KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type) 74 75# Currently, disable -Wstringop-overflow for GCC 11, globally. 76KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-option, -Wno-stringop-overflow) 77KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow) 78 79# Currently, disable -Wunterminated-string-initialization as broken 80KBUILD_CFLAGS += $(call cc-option, -Wno-unterminated-string-initialization) 81 82# The allocators already balk at large sizes, so silence the compiler 83# warnings for bounds checks involving those possible values. While 84# -Wno-alloc-size-larger-than would normally be used here, earlier versions 85# of gcc (<9.1) weirdly don't handle the option correctly when _other_ 86# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX 87# doesn't work (as it is documented to), silently resolving to "0" prior to 88# version 9.1 (and producing an error more recently). Numeric values larger 89# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently 90# ignored, continuing to default to PTRDIFF_MAX. So, left with no other 91# choice, we must perform a versioned check to disable this warning. 92# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au 93KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than 94KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH) 95 96# Prohibit date/time macros, which would make the build non-deterministic 97KBUILD_CFLAGS += -Werror=date-time 98 99# enforce correct pointer usage 100KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types) 101 102# Require designated initializers for all marked structures 103KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init) 104 105# Warn if there is an enum types mismatch 106KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion) 107 108KBUILD_CFLAGS += -Wunused 109 110# 111# W=1 - warnings which may be relevant and do not occur too often 112# 113ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),) 114 115KBUILD_CFLAGS += -Wmissing-format-attribute 116KBUILD_CFLAGS += -Wmissing-include-dirs 117KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable) 118 119KBUILD_CPPFLAGS += -Wundef 120KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1 121 122else 123 124# Some diagnostics enabled by default are noisy. 125# Suppress them by using -Wno... except for W=1. 126KBUILD_CFLAGS += $(call cc-option, -Wno-unused-but-set-variable) 127KBUILD_CFLAGS += $(call cc-option, -Wno-unused-const-variable) 128KBUILD_CFLAGS += $(call cc-option, -Wno-packed-not-aligned) 129KBUILD_CFLAGS += $(call cc-option, -Wno-format-overflow) 130ifdef CONFIG_CC_IS_GCC 131KBUILD_CFLAGS += $(call cc-option, -Wno-format-truncation) 132endif 133KBUILD_CFLAGS += $(call cc-option, -Wno-stringop-truncation) 134 135KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang 136 137ifdef CONFIG_CC_IS_CLANG 138# Clang before clang-16 would warn on default argument promotions. 139ifneq ($(call clang-min-version, 160000),y) 140# Disable -Wformat 141KBUILD_CFLAGS += -Wno-format 142# Then re-enable flags that were part of the -Wformat group that aren't 143# problematic. 144KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier 145KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull 146# Requires clang-12+. 147ifeq ($(call clang-min-version, 120000),y) 148KBUILD_CFLAGS += -Wformat-insufficient-args 149endif 150endif 151KBUILD_CFLAGS += $(call cc-option, -Wno-pointer-to-enum-cast) 152KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare 153KBUILD_CFLAGS += $(call cc-option, -Wno-unaligned-access) 154KBUILD_CFLAGS += -Wno-enum-compare-conditional 155endif 156 157endif 158 159# 160# W=2 - warnings which occur quite often but may still be relevant 161# 162ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),) 163 164KBUILD_CFLAGS += -Wdisabled-optimization 165KBUILD_CFLAGS += -Wshadow 166KBUILD_CFLAGS += $(call cc-option, -Wlogical-op) 167KBUILD_CFLAGS += $(call cc-option, -Wunused-macros) 168 169KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2 170 171else 172 173# The following turn off the warnings enabled by -Wextra 174KBUILD_CFLAGS += -Wno-missing-field-initializers 175KBUILD_CFLAGS += -Wno-type-limits 176KBUILD_CFLAGS += -Wno-shift-negative-value 177 178ifdef CONFIG_CC_IS_CLANG 179KBUILD_CFLAGS += -Wno-enum-enum-conversion 180endif 181 182ifdef CONFIG_CC_IS_GCC 183KBUILD_CFLAGS += -Wno-maybe-uninitialized 184endif 185 186endif 187 188# 189# W=3 - more obscure warnings, can most likely be ignored 190# 191ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),) 192 193KBUILD_CFLAGS += -Wbad-function-cast 194KBUILD_CFLAGS += -Wcast-align 195KBUILD_CFLAGS += -Wcast-qual 196KBUILD_CFLAGS += -Wconversion 197KBUILD_CFLAGS += -Wpacked 198KBUILD_CFLAGS += -Wpadded 199KBUILD_CFLAGS += -Wpointer-arith 200KBUILD_CFLAGS += -Wredundant-decls 201KBUILD_CFLAGS += -Wsign-compare 202KBUILD_CFLAGS += -Wswitch-default 203 204KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3 205 206else 207 208# The following turn off the warnings enabled by -Wextra 209KBUILD_CFLAGS += -Wno-sign-compare 210KBUILD_CFLAGS += -Wno-unused-parameter 211 212endif 213 214# 215# W=e and CONFIG_WERROR - error out on warnings 216# 217ifneq ($(findstring e, $(KBUILD_EXTRA_WARN))$(CONFIG_WERROR),) 218 219KBUILD_CPPFLAGS += -Werror 220KBUILD_AFLAGS += -Wa,--fatal-warnings 221KBUILD_LDFLAGS += --fatal-warnings 222KBUILD_USERCFLAGS += -Werror 223KBUILD_USERLDFLAGS += -Wl,--fatal-warnings 224KBUILD_RUSTFLAGS += -Dwarnings 225 226# While hostprog flags are used during build bootstrapping (thus should not 227# depend on CONFIG_ symbols), -Werror is disruptive and should be opted into. 228# Only apply -Werror to hostprogs built after the initial Kconfig stage. 229KBUILD_HOSTCFLAGS += -Werror 230KBUILD_HOSTLDFLAGS += -Wl,--fatal-warnings 231KBUILD_HOSTRUSTFLAGS += -Dwarnings 232 233endif 234