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-disable-warning, frame-address)
20KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
21KBUILD_CFLAGS += -Wmissing-declarations
22KBUILD_CFLAGS += -Wmissing-prototypes
23
24ifneq ($(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-disable-warning, format-overflow-non-kprintf)
39KBUILD_CFLAGS += $(call cc-disable-warning, 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-disable-warning, 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-disable-warning, dangling-pointer)
60
61# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
62KBUILD_CFLAGS += -Wvla
63
64# disable pointer signed / unsigned warnings in gcc 4.0
65KBUILD_CFLAGS += -Wno-pointer-sign
66
67# In order to make sure new function cast mismatches are not introduced
68# in the kernel (to avoid tripping CFI checking), the kernel should be
69# globally built with -Wcast-function-type.
70KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)
71
72# Currently, disable -Wstringop-overflow for GCC 11, globally.
73KBUILD_CFLAGS-$(CONFIG_CC_NO_STRINGOP_OVERFLOW) += $(call cc-disable-warning, stringop-overflow)
74KBUILD_CFLAGS-$(CONFIG_CC_STRINGOP_OVERFLOW) += $(call cc-option, -Wstringop-overflow)
75
76# Currently, disable -Wunterminated-string-initialization as broken
77KBUILD_CFLAGS += $(call cc-disable-warning, unterminated-string-initialization)
78
79# The allocators already balk at large sizes, so silence the compiler
80# warnings for bounds checks involving those possible values. While
81# -Wno-alloc-size-larger-than would normally be used here, earlier versions
82# of gcc (<9.1) weirdly don't handle the option correctly when _other_
83# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX
84# doesn't work (as it is documented to), silently resolving to "0" prior to
85# version 9.1 (and producing an error more recently). Numeric values larger
86# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently
87# ignored, continuing to default to PTRDIFF_MAX. So, left with no other
88# choice, we must perform a versioned check to disable this warning.
89# https://lore.kernel.org/lkml/20210824115859.187f272f@canb.auug.org.au
90KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than
91KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
92
93# Prohibit date/time macros, which would make the build non-deterministic
94KBUILD_CFLAGS += -Werror=date-time
95
96# enforce correct pointer usage
97KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types)
98
99# Require designated initializers for all marked structures
100KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
101
102# Warn if there is an enum types mismatch
103KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
104
105KBUILD_CFLAGS += -Wunused
106
107#
108# W=1 - warnings which may be relevant and do not occur too often
109#
110ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
111
112KBUILD_CFLAGS += -Wmissing-format-attribute
113KBUILD_CFLAGS += -Wmissing-include-dirs
114KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)
115
116KBUILD_CPPFLAGS += -Wundef
117KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
118
119else
120
121# Some diagnostics enabled by default are noisy.
122# Suppress them by using -Wno... except for W=1.
123KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
124KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
125KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
126KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
127ifdef CONFIG_CC_IS_GCC
128KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
129endif
130KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
131
132KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang
133
134ifdef CONFIG_CC_IS_CLANG
135# Clang before clang-16 would warn on default argument promotions.
136ifneq ($(call clang-min-version, 160000),y)
137# Disable -Wformat
138KBUILD_CFLAGS += -Wno-format
139# Then re-enable flags that were part of the -Wformat group that aren't
140# problematic.
141KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier
142KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull
143# Requires clang-12+.
144ifeq ($(call clang-min-version, 120000),y)
145KBUILD_CFLAGS += -Wformat-insufficient-args
146endif
147endif
148KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
149KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
150KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
151KBUILD_CFLAGS += -Wno-enum-compare-conditional
152endif
153
154endif
155
156#
157# W=2 - warnings which occur quite often but may still be relevant
158#
159ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
160
161KBUILD_CFLAGS += -Wdisabled-optimization
162KBUILD_CFLAGS += -Wshadow
163KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
164KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
165
166KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2
167
168else
169
170# The following turn off the warnings enabled by -Wextra
171KBUILD_CFLAGS += -Wno-missing-field-initializers
172KBUILD_CFLAGS += -Wno-type-limits
173KBUILD_CFLAGS += -Wno-shift-negative-value
174
175ifdef CONFIG_CC_IS_CLANG
176KBUILD_CFLAGS += -Wno-enum-enum-conversion
177endif
178
179ifdef CONFIG_CC_IS_GCC
180KBUILD_CFLAGS += -Wno-maybe-uninitialized
181endif
182
183endif
184
185#
186# W=3 - more obscure warnings, can most likely be ignored
187#
188ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),)
189
190KBUILD_CFLAGS += -Wbad-function-cast
191KBUILD_CFLAGS += -Wcast-align
192KBUILD_CFLAGS += -Wcast-qual
193KBUILD_CFLAGS += -Wconversion
194KBUILD_CFLAGS += -Wpacked
195KBUILD_CFLAGS += -Wpadded
196KBUILD_CFLAGS += -Wpointer-arith
197KBUILD_CFLAGS += -Wredundant-decls
198KBUILD_CFLAGS += -Wsign-compare
199KBUILD_CFLAGS += -Wswitch-default
200
201KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3
202
203else
204
205# The following turn off the warnings enabled by -Wextra
206KBUILD_CFLAGS += -Wno-sign-compare
207KBUILD_CFLAGS += -Wno-unused-parameter
208
209endif
210
211#
212# W=e - error out on warnings
213#
214ifneq ($(findstring e, $(KBUILD_EXTRA_WARN)),)
215
216KBUILD_CFLAGS += -Werror
217
218endif
219