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lib: typesafe hash table breadcrumbs

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Looking at the coverity report, it complains that tabshift could be
zero, resulting in a uint32_t shifted by 33 (which is undefined.)

As I was confused by the "+ 1", in addition to the SA assume(), leave
some breadcumbs for next time this comes up.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
This commit is contained in:
David Lamparter 2023-04-21 16:15:11 +02:00
parent 4dbef8567b
commit ae19023b8e
2 changed files with 20 additions and 2 deletions
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9
lib/typesafe.c
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@ -85,6 +85,15 @@ void typesafe_hash_grow(struct thash_head *head)
uint32_t newsize = head->count, i, j;
uint8_t newshift, delta;
/* note hash_grow is called after head->count++, so newsize is
* guaranteed to be >= 1. So the minimum argument to builtin_ctz
* below is 2, which returns 1, and that makes newshift >= 2.
*
* Calling hash_grow with a zero head->count would result in a
* malformed hash table that has tabshift == 1.
*/
assert(head->count > 0);
hash_consistency_check(head);
newsize |= newsize >> 1;

13
lib/typesafe.h
View File

@ -783,6 +783,12 @@ struct thash_head {
struct thash_item **entries;
uint32_t count;
/* tabshift can be 0 if the hash table is empty and entries is NULL.
* otherwise it will always be 2 or larger because it contains
* the shift value *plus 1*. This is a trick to make HASH_SIZE return
* the correct value (with the >> 1) for tabshift == 0, without needing
* a conditional branch.
*/
uint8_t tabshift;
uint8_t minshift, maxshift;
};
@ -791,8 +797,11 @@ struct thash_head {
((1U << (tabshift)) >> 1)
#define HASH_SIZE(head) \
_HASH_SIZE((head).tabshift)
#define _HASH_KEY(tabshift, val) \
((val) >> (33 - (tabshift)))
#define _HASH_KEY(tabshift, val) \
({ \
assume((tabshift) >= 2 && (tabshift) <= 33); \
(val) >> (33 - (tabshift)); \
})
#define HASH_KEY(head, val) \
_HASH_KEY((head).tabshift, val)
#define HASH_GROW_THRESHOLD(head) \