linux-kernel - [PATCH] lib/siphash.c: mark expected switch fall-throughs

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Date:   Tue, 16 Apr 2019 17:27:20 +1000
From:   Stephen Rothwell <sfr@...b.auug.org.au>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        Kees Cook <keescook@...omium.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: [PATCH] lib/siphash.c: mark expected switch fall-throughs

In preparation to enabling -Wimplicit-fallthrough, mark switch cases
where we are expecting to fall through.

This patch aims to suppress up to 18 missing-break-in-switch false
positives on some architectures.

Cc: Jason A. Donenfeld <Jason@...c4.com>
Cc: Gustavo A. R. Silva <gustavo@...eddedor.com>
Cc: Kees Cook <keescook@...omium.org>
Signed-off-by: Stephen Rothwell <sfr@...b.auug.org.au>
---
 lib/siphash.c | 36 ++++++++++++++++++------------------
 1 file changed, 18 insertions(+), 18 deletions(-)

Build tested on PowerPC.

diff --git a/lib/siphash.c b/lib/siphash.c
index 3ae58b4edad6..c47bb6ff2149 100644
--- a/lib/siphash.c
+++ b/lib/siphash.c
@@ -68,11 +68,11 @@ u64 __siphash_aligned(const void *data, size_t len, const siphash_key_t *key)
 						  bytemask_from_count(left)));
 #else
 	switch (left) {
-	case 7: b |= ((u64)end[6]) << 48;
-	case 6: b |= ((u64)end[5]) << 40;
-	case 5: b |= ((u64)end[4]) << 32;
+	case 7: b |= ((u64)end[6]) << 48; /* fall through */
+	case 6: b |= ((u64)end[5]) << 40; /* fall through */
+	case 5: b |= ((u64)end[4]) << 32; /* fall through */
 	case 4: b |= le32_to_cpup(data); break;
-	case 3: b |= ((u64)end[2]) << 16;
+	case 3: b |= ((u64)end[2]) << 16; /* fall through */
 	case 2: b |= le16_to_cpup(data); break;
 	case 1: b |= end[0];
 	}
@@ -101,11 +101,11 @@ u64 __siphash_unaligned(const void *data, size_t len, const siphash_key_t *key)
 						  bytemask_from_count(left)));
 #else
 	switch (left) {
-	case 7: b |= ((u64)end[6]) << 48;
-	case 6: b |= ((u64)end[5]) << 40;
-	case 5: b |= ((u64)end[4]) << 32;
+	case 7: b |= ((u64)end[6]) << 48; /* fall through */
+	case 6: b |= ((u64)end[5]) << 40; /* fall through */
+	case 5: b |= ((u64)end[4]) << 32; /* fall through */
 	case 4: b |= get_unaligned_le32(end); break;
-	case 3: b |= ((u64)end[2]) << 16;
+	case 3: b |= ((u64)end[2]) << 16; /* fall through */
 	case 2: b |= get_unaligned_le16(end); break;
 	case 1: b |= end[0];
 	}
@@ -268,11 +268,11 @@ u32 __hsiphash_aligned(const void *data, size_t len, const hsiphash_key_t *key)
 						  bytemask_from_count(left)));
 #else
 	switch (left) {
-	case 7: b |= ((u64)end[6]) << 48;
-	case 6: b |= ((u64)end[5]) << 40;
-	case 5: b |= ((u64)end[4]) << 32;
+	case 7: b |= ((u64)end[6]) << 48; /* fall through */
+	case 6: b |= ((u64)end[5]) << 40; /* fall through */
+	case 5: b |= ((u64)end[4]) << 32; /* fall through */
 	case 4: b |= le32_to_cpup(data); break;
-	case 3: b |= ((u64)end[2]) << 16;
+	case 3: b |= ((u64)end[2]) << 16; /* fall through */
 	case 2: b |= le16_to_cpup(data); break;
 	case 1: b |= end[0];
 	}
@@ -301,11 +301,11 @@ u32 __hsiphash_unaligned(const void *data, size_t len,
 						  bytemask_from_count(left)));
 #else
 	switch (left) {
-	case 7: b |= ((u64)end[6]) << 48;
-	case 6: b |= ((u64)end[5]) << 40;
-	case 5: b |= ((u64)end[4]) << 32;
+	case 7: b |= ((u64)end[6]) << 48; /* fall through */
+	case 6: b |= ((u64)end[5]) << 40; /* fall through */
+	case 5: b |= ((u64)end[4]) << 32; /* fall through */
 	case 4: b |= get_unaligned_le32(end); break;
-	case 3: b |= ((u64)end[2]) << 16;
+	case 3: b |= ((u64)end[2]) << 16; /* fall through */
 	case 2: b |= get_unaligned_le16(end); break;
 	case 1: b |= end[0];
 	}
@@ -431,7 +431,7 @@ u32 __hsiphash_aligned(const void *data, size_t len, const hsiphash_key_t *key)
 		v0 ^= m;
 	}
 	switch (left) {
-	case 3: b |= ((u32)end[2]) << 16;
+	case 3: b |= ((u32)end[2]) << 16; /* fall through */
 	case 2: b |= le16_to_cpup(data); break;
 	case 1: b |= end[0];
 	}
@@ -454,7 +454,7 @@ u32 __hsiphash_unaligned(const void *data, size_t len,
 		v0 ^= m;
 	}
 	switch (left) {
-	case 3: b |= ((u32)end[2]) << 16;
+	case 3: b |= ((u32)end[2]) << 16; /* fall through */
 	case 2: b |= get_unaligned_le16(end); break;
 	case 1: b |= end[0];
 	}
-- 
2.20.1



-- 
Cheers,
Stephen Rothwell

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