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SubjectRe: [PATCH] lib/stackdepot: use a non-instrumented version of memcmp()
On Thu, Nov 16, 2017 at 4:08 PM, Andrey Ryabinin
<aryabinin@virtuozzo.com> wrote:
>
>
> On 11/15/2017 08:34 PM, Alexander Potapenko wrote:
>> stackdepot used to call memcmp(), which compiler tools normally
>> instrument, therefore every lookup used to unnecessarily call
>> instrumented code.
>> This is somewhat ok in the case of KASAN, but under KMSAN a lot of time
>> was spent in the instrumentation.
>>
>> Signed-off-by: Alexander Potapenko <glider@google.com>
>> ---
>> lib/stackdepot.c | 21 ++++++++++++++++++---
>> 1 file changed, 18 insertions(+), 3 deletions(-)
>>
>> diff --git a/lib/stackdepot.c b/lib/stackdepot.c
>> index f87d138e9672..d372101e8dc2 100644
>> --- a/lib/stackdepot.c
>> +++ b/lib/stackdepot.c
>> @@ -163,6 +163,23 @@ static inline u32 hash_stack(unsigned long *entries, unsigned int size)
>> STACK_HASH_SEED);
>> }
>>
>> +/* Use our own, non-instrumented version of memcmp().
>> + *
>> + * We actually don't care about the order, just the equality.
>> + */
>> +static inline
>> +int stackdepot_memcmp(const void *s1, const void *s2, unsigned int n)
>> +{
>
> Why 'void *' types? The function treats s1, s2 as array of long, also 'n' is number of longs here.
Agreed. I started with a plain memcpy, so the arg types were left over.
>> + unsigned long *u1 = (unsigned long *)s1;
>> + unsigned long *u2 = (unsigned long *)s2;
>> +
>> + for ( ; n-- ; u1++, u2++) {
>> + if (*u1 != *u2)
>> + return 1;
>> + }
>> + return 0;
>> +}
>> +
>> /* Find a stack that is equal to the one stored in entries in the hash */
>> static inline struct stack_record *find_stack(struct stack_record *bucket,
>> unsigned long *entries, int size,
>> @@ -173,10 +190,8 @@ static inline struct stack_record *find_stack(struct stack_record *bucket,
>> for (found = bucket; found; found = found->next) {
>> if (found->hash == hash &&
>> found->size == size &&
>> - !memcmp(entries, found->entries,
>> - size * sizeof(unsigned long))) {
>> + !stackdepot_memcmp(entries, found->entries, size))
>> return found;
>> - }
>> }
>> return NULL;
>> }
>>



--
Alexander Potapenko
Software Engineer

Google Germany GmbH
Erika-Mann-Straße, 33
80636 München

Geschäftsführer: Paul Manicle, Halimah DeLaine Prado
Registergericht und -nummer: Hamburg, HRB 86891
Sitz der Gesellschaft: Hamburg
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