[PATCH v2] kbuild: Change fallthrough comments to attributes
From: Nathan Huckleberry
Date: Mon Aug 12 2019 - 18:14:37 EST
Clang does not support the use of comments to label
intentional fallthrough. This patch replaces some uses
of comments to attributesto cut down a significant number
of warnings on clang (from ~50000 to ~200). Only comments
in commonly used header files have been replaced.
Since there is still quite a bit of noise, this
patch moves -Wimplicit-fallthrough to
Makefile.extrawarn if you are compiling with
clang.
Signed-off-by: Nathan Huckleberry <nhuck@xxxxxxxxxx>
---
Makefile | 4 ++
include/linux/compiler_attributes.h | 4 ++
include/linux/jhash.h | 60 +++++++++++++++++++++--------
include/linux/mm.h | 9 +++--
include/linux/signal.h | 14 ++++---
include/linux/skbuff.h | 12 +++---
lib/zstd/bitstream.h | 10 ++---
scripts/Makefile.extrawarn | 3 ++
8 files changed, 81 insertions(+), 35 deletions(-)
diff --git a/Makefile b/Makefile
index 1b23f95db176..93b9744e66a2 100644
--- a/Makefile
+++ b/Makefile
@@ -846,7 +846,11 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include)
KBUILD_CFLAGS += -Wdeclaration-after-statement
# Warn about unmarked fall-throughs in switch statement.
+# If the compiler is clang, this warning is only enabled if W=1 in
+# Makefile.extrawarn
+ifndef CONFIG_CC_IS_CLANG
KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
+endif
# Variable Length Arrays (VLAs) should not be used anywhere in the kernel
KBUILD_CFLAGS += -Wvla
diff --git a/include/linux/compiler_attributes.h b/include/linux/compiler_attributes.h
index 6b318efd8a74..86c26bc0ace5 100644
--- a/include/linux/compiler_attributes.h
+++ b/include/linux/compiler_attributes.h
@@ -253,4 +253,8 @@
*/
#define __weak __attribute__((__weak__))
+#if __has_attribute(fallthrough)
+#define __fallthrough __attribute__((fallthrough))
+#endif
+
#endif /* __LINUX_COMPILER_ATTRIBUTES_H */
diff --git a/include/linux/jhash.h b/include/linux/jhash.h
index ba2f6a9776b6..1d21e3f32823 100644
--- a/include/linux/jhash.h
+++ b/include/linux/jhash.h
@@ -86,19 +86,43 @@ static inline u32 jhash(const void *key, u32 length, u32 initval)
}
/* Last block: affect all 32 bits of (c) */
switch (length) {
- case 12: c += (u32)k[11]<<24; /* fall through */
- case 11: c += (u32)k[10]<<16; /* fall through */
- case 10: c += (u32)k[9]<<8; /* fall through */
- case 9: c += k[8]; /* fall through */
- case 8: b += (u32)k[7]<<24; /* fall through */
- case 7: b += (u32)k[6]<<16; /* fall through */
- case 6: b += (u32)k[5]<<8; /* fall through */
- case 5: b += k[4]; /* fall through */
- case 4: a += (u32)k[3]<<24; /* fall through */
- case 3: a += (u32)k[2]<<16; /* fall through */
- case 2: a += (u32)k[1]<<8; /* fall through */
- case 1: a += k[0];
+ case 12:
+ c += (u32)k[11]<<24;
+ __fallthrough;
+ case 11:
+ c += (u32)k[10]<<16;
+ __fallthrough;
+ case 10:
+ c += (u32)k[9]<<8;
+ __fallthrough;
+ case 9:
+ c += k[8];
+ __fallthrough;
+ case 8:
+ b += (u32)k[7]<<24;
+ __fallthrough;
+ case 7:
+ b += (u32)k[6]<<16;
+ __fallthrough;
+ case 6:
+ b += (u32)k[5]<<8;
+ __fallthrough;
+ case 5:
+ b += k[4];
+ __fallthrough;
+ case 4:
+ a += (u32)k[3]<<24;
+ __fallthrough;
+ case 3:
+ a += (u32)k[2]<<16;
+ __fallthrough;
+ case 2:
+ a += (u32)k[1]<<8;
+ __fallthrough;
+ case 1:
+ a += k[0];
__jhash_final(a, b, c);
+ break;
case 0: /* Nothing left to add */
break;
}
@@ -132,10 +156,16 @@ static inline u32 jhash2(const u32 *k, u32 length, u32 initval)
/* Handle the last 3 u32's */
switch (length) {
- case 3: c += k[2]; /* fall through */
- case 2: b += k[1]; /* fall through */
- case 1: a += k[0];
+ case 3:
+ c += k[2];
+ __fallthrough;
+ case 2:
+ b += k[1];
+ __fallthrough;
+ case 1:
+ a += k[0];
__jhash_final(a, b, c);
+ break;
case 0: /* Nothing left to add */
break;
}
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 0334ca97c584..7acb131e287f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -158,11 +158,14 @@ static inline void __mm_zero_struct_page(struct page *page)
switch (sizeof(struct page)) {
case 80:
- _pp[9] = 0; /* fallthrough */
+ _pp[9] = 0;
+ __fallthrough;
case 72:
- _pp[8] = 0; /* fallthrough */
+ _pp[8] = 0;
+ __fallthrough;
case 64:
- _pp[7] = 0; /* fallthrough */
+ _pp[7] = 0;
+ __fallthrough;
case 56:
_pp[6] = 0;
_pp[5] = 0;
diff --git a/include/linux/signal.h b/include/linux/signal.h
index b5d99482d3fe..fb750e87566f 100644
--- a/include/linux/signal.h
+++ b/include/linux/signal.h
@@ -129,11 +129,11 @@ static inline void name(sigset_t *r, const sigset_t *a, const sigset_t *b) \
b3 = b->sig[3]; b2 = b->sig[2]; \
r->sig[3] = op(a3, b3); \
r->sig[2] = op(a2, b2); \
- /* fall through */ \
+ __fallthrough; \
case 2: \
a1 = a->sig[1]; b1 = b->sig[1]; \
r->sig[1] = op(a1, b1); \
- /* fall through */ \
+ __fallthrough; \
case 1: \
a0 = a->sig[0]; b0 = b->sig[0]; \
r->sig[0] = op(a0, b0); \
@@ -163,9 +163,9 @@ static inline void name(sigset_t *set) \
switch (_NSIG_WORDS) { \
case 4: set->sig[3] = op(set->sig[3]); \
set->sig[2] = op(set->sig[2]); \
- /* fall through */ \
+ __fallthrough; \
case 2: set->sig[1] = op(set->sig[1]); \
- /* fall through */ \
+ __fallthrough; \
case 1: set->sig[0] = op(set->sig[0]); \
break; \
default: \
@@ -186,7 +186,7 @@ static inline void sigemptyset(sigset_t *set)
memset(set, 0, sizeof(sigset_t));
break;
case 2: set->sig[1] = 0;
- /* fall through */
+ __fallthrough;
case 1: set->sig[0] = 0;
break;
}
@@ -199,7 +199,7 @@ static inline void sigfillset(sigset_t *set)
memset(set, -1, sizeof(sigset_t));
break;
case 2: set->sig[1] = -1;
- /* fall through */
+ __fallthrough;
case 1: set->sig[0] = -1;
break;
}
@@ -230,6 +230,7 @@ static inline void siginitset(sigset_t *set, unsigned long mask)
memset(&set->sig[1], 0, sizeof(long)*(_NSIG_WORDS-1));
break;
case 2: set->sig[1] = 0;
+ __fallthrough;
case 1: ;
}
}
@@ -242,6 +243,7 @@ static inline void siginitsetinv(sigset_t *set, unsigned long mask)
memset(&set->sig[1], -1, sizeof(long)*(_NSIG_WORDS-1));
break;
case 2: set->sig[1] = -1;
+ __fallthrough;
case 1: ;
}
}
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index d8af86d995d6..1b7d3cf81dd8 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -3639,19 +3639,19 @@ static inline bool __skb_metadata_differs(const struct sk_buff *skb_a,
#define __it(x, op) (x -= sizeof(u##op))
#define __it_diff(a, b, op) (*(u##op *)__it(a, op)) ^ (*(u##op *)__it(b, op))
case 32: diffs |= __it_diff(a, b, 64);
- /* fall through */
+ __fallthrough;
case 24: diffs |= __it_diff(a, b, 64);
- /* fall through */
+ __fallthrough;
case 16: diffs |= __it_diff(a, b, 64);
- /* fall through */
+ __fallthrough;
case 8: diffs |= __it_diff(a, b, 64);
break;
case 28: diffs |= __it_diff(a, b, 64);
- /* fall through */
+ __fallthrough;
case 20: diffs |= __it_diff(a, b, 64);
- /* fall through */
+ __fallthrough;
case 12: diffs |= __it_diff(a, b, 64);
- /* fall through */
+ __fallthrough;
case 4: diffs |= __it_diff(a, b, 32);
break;
}
diff --git a/lib/zstd/bitstream.h b/lib/zstd/bitstream.h
index 3a49784d5c61..36c9aeafd801 100644
--- a/lib/zstd/bitstream.h
+++ b/lib/zstd/bitstream.h
@@ -259,15 +259,15 @@ ZSTD_STATIC size_t BIT_initDStream(BIT_DStream_t *bitD, const void *srcBuffer, s
bitD->bitContainer = *(const BYTE *)(bitD->start);
switch (srcSize) {
case 7: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[6]) << (sizeof(bitD->bitContainer) * 8 - 16);
- /* fall through */
+ __fallthrough;
case 6: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[5]) << (sizeof(bitD->bitContainer) * 8 - 24);
- /* fall through */
+ __fallthrough;
case 5: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[4]) << (sizeof(bitD->bitContainer) * 8 - 32);
- /* fall through */
+ __fallthrough;
case 4: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[3]) << 24;
- /* fall through */
+ __fallthrough;
case 3: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[2]) << 16;
- /* fall through */
+ __fallthrough;
case 2: bitD->bitContainer += (size_t)(((const BYTE *)(srcBuffer))[1]) << 8;
default:;
}
diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
index a74ce2e3c33e..e12359d69bb7 100644
--- a/scripts/Makefile.extrawarn
+++ b/scripts/Makefile.extrawarn
@@ -30,6 +30,9 @@ warning-1 += $(call cc-option, -Wunused-but-set-variable)
warning-1 += $(call cc-option, -Wunused-const-variable)
warning-1 += $(call cc-option, -Wpacked-not-aligned)
warning-1 += $(call cc-option, -Wstringop-truncation)
+ifdef CONFIG_CC_IS_CLANG
+KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,)
+endif
# The following turn off the warnings enabled by -Wextra
warning-1 += -Wno-missing-field-initializers
warning-1 += -Wno-sign-compare
--
2.23.0.rc1.153.gdeed80330f-goog