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 += -Wundef
12KBUILD_CFLAGS += -Werror=implicit-function-declaration
13KBUILD_CFLAGS += -Werror=implicit-int
14KBUILD_CFLAGS += -Werror=return-type
15KBUILD_CFLAGS += -Werror=strict-prototypes
16KBUILD_CFLAGS += -Wno-format-security
17KBUILD_CFLAGS += -Wno-trigraphs
18KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,)
19KBUILD_CFLAGS += $(call cc-disable-warning, address-of-packed-member)
20KBUILD_CFLAGS += -Wmissing-declarations
21KBUILD_CFLAGS += -Wmissing-prototypes
22
23ifneq ($(CONFIG_FRAME_WARN),0)
24KBUILD_CFLAGS += -Wframe-larger-than=$(CONFIG_FRAME_WARN)
25endif
26
27KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror
28KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y)
29KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
30
31ifdef CONFIG_CC_IS_CLANG
32# The kernel builds with '-std=gnu11' so use of GNU extensions is acceptable.
33KBUILD_CFLAGS += -Wno-gnu
34
35# Clang checks for overflow/truncation with '%p', while GCC does not:
36# https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111219
37KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow-non-kprintf)
38KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation-non-kprintf)
39else
40
41# gcc inanely warns about local variables called 'main'
42KBUILD_CFLAGS += -Wno-main
43endif
44
45# These result in bogus false positives
46KBUILD_CFLAGS += $(call cc-disable-warning, dangling-pointer)
47
48# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
49KBUILD_CFLAGS += -Wvla
50
51# disable pointer signed / unsigned warnings in gcc 4.0
52KBUILD_CFLAGS += -Wno-pointer-sign
53
54# In order to make sure new function cast mismatches are not introduced
55# in the kernel (to avoid tripping CFI checking), the kernel should be
56# globally built with -Wcast-function-type.
57KBUILD_CFLAGS += $(call cc-option, -Wcast-function-type)
58
59# The allocators already balk at large sizes, so silence the compiler
60# warnings for bounds checks involving those possible values. While
61# -Wno-alloc-size-larger-than would normally be used here, earlier versions
62# of gcc (<9.1) weirdly don't handle the option correctly when _other_
63# warnings are produced (?!). Using -Walloc-size-larger-than=SIZE_MAX
64# doesn't work (as it is documented to), silently resolving to "0" prior to
65# version 9.1 (and producing an error more recently). Numeric values larger
66# than PTRDIFF_MAX also don't work prior to version 9.1, which are silently
67# ignored, continuing to default to PTRDIFF_MAX. So, left with no other
68# choice, we must perform a versioned check to disable this warning.
69# https://lore.kernel.org/lkml/[email protected]
70KBUILD_CFLAGS-$(call gcc-min-version, 90100) += -Wno-alloc-size-larger-than
71KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
72
73# Prohibit date/time macros, which would make the build non-deterministic
74KBUILD_CFLAGS += -Werror=date-time
75
76# enforce correct pointer usage
77KBUILD_CFLAGS += $(call cc-option,-Werror=incompatible-pointer-types)
78
79# Require designated initializers for all marked structures
80KBUILD_CFLAGS += $(call cc-option,-Werror=designated-init)
81
82# Warn if there is an enum types mismatch
83KBUILD_CFLAGS += $(call cc-option,-Wenum-conversion)
84
85# Explicitly clear padding bits during variable initialization
86KBUILD_CFLAGS += $(call cc-option,-fzero-init-padding-bits=all)
87
88KBUILD_CFLAGS += -Wextra
89KBUILD_CFLAGS += -Wunused
90
91#
92# W=1 - warnings which may be relevant and do not occur too often
93#
94ifneq ($(findstring 1, $(KBUILD_EXTRA_WARN)),)
95
96KBUILD_CFLAGS += -Wmissing-format-attribute
97KBUILD_CFLAGS += -Wmissing-include-dirs
98KBUILD_CFLAGS += $(call cc-option, -Wunused-const-variable)
99
100KBUILD_CPPFLAGS += -Wundef
101KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN1
102
103else
104
105# Some diagnostics enabled by default are noisy.
106# Suppress them by using -Wno... except for W=1.
107KBUILD_CFLAGS += $(call cc-disable-warning, unused-but-set-variable)
108KBUILD_CFLAGS += $(call cc-disable-warning, unused-const-variable)
109KBUILD_CFLAGS += $(call cc-disable-warning, packed-not-aligned)
110KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
111ifdef CONFIG_CC_IS_GCC
112KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
113endif
114KBUILD_CFLAGS += $(call cc-disable-warning, stringop-truncation)
115
116KBUILD_CFLAGS += -Wno-override-init # alias for -Wno-initializer-overrides in clang
117
118ifdef CONFIG_CC_IS_CLANG
119# Clang before clang-16 would warn on default argument promotions.
120ifneq ($(call clang-min-version, 160000),y)
121# Disable -Wformat
122KBUILD_CFLAGS += -Wno-format
123# Then re-enable flags that were part of the -Wformat group that aren't
124# problematic.
125KBUILD_CFLAGS += -Wformat-extra-args -Wformat-invalid-specifier
126KBUILD_CFLAGS += -Wformat-zero-length -Wnonnull
127# Requires clang-12+.
128ifeq ($(call clang-min-version, 120000),y)
129KBUILD_CFLAGS += -Wformat-insufficient-args
130endif
131endif
132KBUILD_CFLAGS += $(call cc-disable-warning, pointer-to-enum-cast)
133KBUILD_CFLAGS += -Wno-tautological-constant-out-of-range-compare
134KBUILD_CFLAGS += $(call cc-disable-warning, unaligned-access)
135KBUILD_CFLAGS += -Wno-enum-compare-conditional
136endif
137
138endif
139
140#
141# W=2 - warnings which occur quite often but may still be relevant
142#
143ifneq ($(findstring 2, $(KBUILD_EXTRA_WARN)),)
144
145KBUILD_CFLAGS += -Wdisabled-optimization
146KBUILD_CFLAGS += -Wshadow
147KBUILD_CFLAGS += $(call cc-option, -Wlogical-op)
148KBUILD_CFLAGS += $(call cc-option, -Wunused-macros)
149
150KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN2
151
152else
153
154# The following turn off the warnings enabled by -Wextra
155KBUILD_CFLAGS += -Wno-missing-field-initializers
156KBUILD_CFLAGS += -Wno-type-limits
157KBUILD_CFLAGS += -Wno-shift-negative-value
158
159ifdef CONFIG_CC_IS_CLANG
160KBUILD_CFLAGS += -Wno-enum-enum-conversion
161endif
162
163ifdef CONFIG_CC_IS_GCC
164KBUILD_CFLAGS += -Wno-maybe-uninitialized
165endif
166
167endif
168
169#
170# W=3 - more obscure warnings, can most likely be ignored
171#
172ifneq ($(findstring 3, $(KBUILD_EXTRA_WARN)),)
173
174KBUILD_CFLAGS += -Wbad-function-cast
175KBUILD_CFLAGS += -Wcast-align
176KBUILD_CFLAGS += -Wcast-qual
177KBUILD_CFLAGS += -Wconversion
178KBUILD_CFLAGS += -Wpacked
179KBUILD_CFLAGS += -Wpadded
180KBUILD_CFLAGS += -Wpointer-arith
181KBUILD_CFLAGS += -Wredundant-decls
182KBUILD_CFLAGS += -Wsign-compare
183KBUILD_CFLAGS += -Wswitch-default
184
185KBUILD_CPPFLAGS += -DKBUILD_EXTRA_WARN3
186
187else
188
189# The following turn off the warnings enabled by -Wextra
190KBUILD_CFLAGS += -Wno-sign-compare
191KBUILD_CFLAGS += -Wno-unused-parameter
192
193endif
194
195#
196# W=e - error out on warnings
197#
198ifneq ($(findstring e, $(KBUILD_EXTRA_WARN)),)
199
200KBUILD_CFLAGS += -Werror
201
202endif
203