Re: [Xen-devel] Lots of new warnings with gcc-7.1.1

[Jakub Kicinski <kubakici@xxxxx>]

On Tue, 11 Jul 2017 15:35:15 -0700, Linus Torvalds wrote:
> I do suspect I'll make "-Wformat-truncation" (as opposed to
> "-Wformat-overflow") be a "V=1" kind of warning.  But let's see how
> many of these we can fix, ok?

Somehow related - what's the stand on -Wimplicit-fallthrough?  I run
into the jump tables in jhash.h generating lots of warnings.  Is it OK
to do this?

--->8------

diff --git a/include/linux/jhash.h b/include/linux/jhash.h
index 348c6f47e4cc..f6d6513a4c03 100644
--- a/include/linux/jhash.h
+++ b/include/linux/jhash.h
@@ -85,20 +85,19 @@ static inline u32 jhash(const void *key, u32 length, u32 
initval)
                k += 12;
        }
        /* Last block: affect all 32 bits of (c) */
-       /* All the case statements fall through */
        switch (length) {
-       case 12: c += (u32)k[11]<<24;
-       case 11: c += (u32)k[10]<<16;
-       case 10: c += (u32)k[9]<<8;
-       case 9:  c += k[8];
-       case 8:  b += (u32)k[7]<<24;
-       case 7:  b += (u32)k[6]<<16;
-       case 6:  b += (u32)k[5]<<8;
-       case 5:  b += k[4];
-       case 4:  a += (u32)k[3]<<24;
-       case 3:  a += (u32)k[2]<<16;
-       case 2:  a += (u32)k[1]<<8;
-       case 1:  a += k[0];
+       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];             /* fall through */
                 __jhash_final(a, b, c);
        case 0: /* Nothing left to add */
                break;
@@ -131,11 +130,11 @@ static inline u32 jhash2(const u32 *k, u32 length, u32 
initval)
                k += 3;
        }
 
-       /* Handle the last 3 u32's: all the case statements fall through */
+       /* Handle the last 3 u32's */
        switch (length) {
-       case 3: c += k[2];
-       case 2: b += k[1];
-       case 1: a += k[0];
+       case 3: c += k[2];      /* fall through */
+       case 2: b += k[1];      /* fall through */
+       case 1: a += k[0];      /* fall through */
                __jhash_final(a, b, c);
        case 0: /* Nothing left to add */
                break;

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