Makefile.warn

  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# 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, $(KBUILD_EXTRA_WARN)),)
194
195KBUILD_CFLAGS += -Wbad-function-cast
196KBUILD_CFLAGS += -Wcast-align
197KBUILD_CFLAGS += -Wcast-qual
198KBUILD_CFLAGS += -Wconversion
199KBUILD_CFLAGS += -Wpacked
200KBUILD_CFLAGS += -Wpadded
201KBUILD_CFLAGS += -Wpointer-arith
202KBUILD_CFLAGS += -Wredundant-decls
203KBUILD_CFLAGS += -Wsign-compare
204KBUILD_CFLAGS += -Wswitch-default
205
206KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3
207
208else
209
210# The following turn off the warnings enabled by -Wextra
211KBUILD_CFLAGS += -Wno-sign-compare
212KBUILD_CFLAGS += -Wno-unused-parameter
213
214endif
215
216#
217# W=e and CONFIG_WERROR - error out on warnings
218#
219ifneq ($(findstring e, $(KBUILD_EXTRA_WARN))$(CONFIG_WERROR),)
220
221KBUILD_CPPFLAGS		+= -Werror
222KBUILD_AFLAGS		+= -Wa,--fatal-warnings
223KBUILD_LDFLAGS		+= --fatal-warnings
224KBUILD_USERCFLAGS	+= -Werror
225KBUILD_USERLDFLAGS	+= -Wl,--fatal-warnings
226KBUILD_RUSTFLAGS	+= -Dwarnings
227
228# While hostprog flags are used during build bootstrapping (thus should not
229# depend on CONFIG_ symbols), -Werror is disruptive and should be opted into.
230# Only apply -Werror to hostprogs built after the initial Kconfig stage.
231KBUILD_HOSTCFLAGS	+= -Werror
232KBUILD_HOSTLDFLAGS	+= -Wl,--fatal-warnings
233KBUILD_HOSTRUSTFLAGS	+= -Dwarnings
234
235endif