On 5/2/24 15:28, Ales Musil wrote: > The pointer was passed to memcpy as uin32_t *, however the hash bytes > might be unaligned at that point. Case it to uint8_t * instead
'Case' ? > which has only single byte alignment requirement. This seems to be > a false positive reported by clang [0]. After thinking some more, it's not actually a false positive per se. According to the C spec we're not actually allowed to have misaligned pointers even if we're not reading/writing through them. So, technically, the initial cast to uint32_t pointer is no correct. I don't think we can fully avoid such casts without loosing type checking, but I think we need to revert changes to hash functions made in commit db5a101931c5 ("clang: Fix the alignment warning."). i.e. we should go back to using uint8_t pointer and cast it on the get_unaligned_u32() call with ALIGNED_CAST. We will still have a misaligned pointer, but it will be immediately cast back, so should cause less issues. Note: all arithmetic should be done on the uint8_t pointer, not a misaligned uin32_t one to avoid potential other UB conditions. Best regards, Ilya Maximets. > > lib/hash.c:46:22: runtime error: load of misaligned address > 0x507000000065 for type 'const uint32_t *' (aka 'const unsigned int *'), > which requires 4 byte alignment > 0x507000000065: note: pointer points here > 73 62 2e 73 6f 63 6b 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 > ^ > 00 00 00 00 00 00 00 00 00 > 0 0x6191cb in hash_bytes ovs/lib/hash.c:46:9 > 1 0x69d064 in hash_string ovs/lib/hash.h:404:12 > 2 0x69d064 in hash_name ovs/lib/shash.c:29:12 > 3 0x69d064 in shash_find ovs/lib/shash.c:237:49 > 4 0x69dada in shash_find_data ovs/lib/shash.c:251:31 > 5 0x507987 in add_remote ovs/ovsdb/ovsdb-server.c:1382:15 > 6 0x507987 in parse_options ovs/ovsdb/ovsdb-server.c:2659:13 > 7 0x507987 in main ovs/ovsdb/ovsdb-server.c:751:5 > > SUMMARY: UndefinedBehaviorSanitizer: undefined-behavior lib/hash.c:46:22 > > [0] https://github.com/llvm/llvm-project/issues/90848 > Signed-off-by: Ales Musil <amu...@redhat.com> > --- > lib/hash.c | 2 +- > lib/jhash.c | 2 +- > 2 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/lib/hash.c b/lib/hash.c > index c722f3c3c..986fa6643 100644 > --- a/lib/hash.c > +++ b/lib/hash.c > @@ -43,7 +43,7 @@ hash_bytes(const void *p_, size_t n, uint32_t basis) > if (n) { > uint32_t tmp = 0; > > - memcpy(&tmp, p, n); > + memcpy(&tmp, (const uint8_t *) p, n); > hash = hash_add(hash, tmp); > } > > diff --git a/lib/jhash.c b/lib/jhash.c > index c59b51b61..0a0628589 100644 > --- a/lib/jhash.c > +++ b/lib/jhash.c > @@ -114,7 +114,7 @@ jhash_bytes(const void *p_, size_t n, uint32_t basis) > uint32_t tmp[3]; > > tmp[0] = tmp[1] = tmp[2] = 0; > - memcpy(tmp, p, n); > + memcpy(tmp, (const uint8_t *) p, n); > a += tmp[0]; > b += tmp[1]; > c += tmp[2]; _______________________________________________ dev mailing list d...@openvswitch.org https://mail.openvswitch.org/mailman/listinfo/ovs-dev