[PATCH v2] parallel-checkout: send the new object_id algo field to the workers
- From
Matheus Tavares <matheus.bernardino@usp.br>
- Date
- May 17, 2021, 19:49 UTC
- Message-ID
- <4e113550d595925e4f458cdcb63c7d90205b389b.1621280649.git.matheus.bernardino@usp.br>
- In-Reply-To
- <a4225bc79d963c5a411105e2b75f9ca4b80de835.1621000916.git.matheus.bernardino@usp.br>
An object_id storing a SHA-1 name has some unused bytes at the end of the hash array. Since these bytes are not used, they are usually not initialized to any value either. However, at parallel_checkout.c:send_one_item() the object_id of a cache entry is copied into a buffer which is later sent to a checkout worker through a pipe write(). This makes Valgrind complain about passing uninitialized bytes to a syscall. The worker won't use these uninitialized bytes either, but the warning could confuse someone trying to debug this code; So instead of using oidcpy(), send_one_item() uses hashcpy() to only copy the used/initialized bytes of the object_id, and leave the remaining part with zeros.
However, since cf0983213c ("hash: add an algo member to struct object_id", 2021-04-26), using hashcpy() is no longer sufficient here as it won't copy the new algo field from the object_id. Let's add and use a new function which meets both our requirements of copying all the important object_id data while still avoiding the uninitialized bytes, by padding the end of the hash array in the destination object_id. With this change, we also no longer need the destination buffer from send_one_item() to be initialized with zeros, so let's switch from xcalloc() to xmalloc() to make this clear.
Signed-off-by: Matheus Tavares <matheus.bernardino@usp.br> ---
There is no change since v1, I'm just dropping the RFC status :)
hash.h | 16 ++++++++++++++++ parallel-checkout.c | 13 ++++++------- 2 files changed, 22 insertions(+), 7 deletions(-)
diff --git a/hash.h b/hash.h index 2986f991c6..9c6df4d952 100644 --- a/hash.h +++ b/hash.h @@ -263,6 +263,22 @@ static inline void oidcpy(struct object_id *dst, const struct object_id *src) dst->algo = src->algo; } +/* Like oidcpy() but zero-pads the unused bytes in dst's hash array. */ +static inline void oidcpy_with_padding(struct object_id *dst, + struct object_id *src) +{ + size_t hashsz; + + if (!src->algo) + hashsz = the_hash_algo->rawsz; + else + hashsz = hash_algos[src->algo].rawsz; + + memcpy(dst->hash, src->hash, hashsz); + memset(dst->hash + hashsz, 0, GIT_MAX_RAWSZ - hashsz); + dst->algo = src->algo; +} + static inline struct object_id *oiddup(const struct object_id *src) { struct object_id *dst = xmalloc(sizeof(struct object_id)); diff --git a/parallel-checkout.c b/parallel-checkout.c index 6b1af32bb3..ddc0ff3c06 100644 --- a/parallel-checkout.c +++ b/parallel-checkout.c @@ -411,7 +411,7 @@ static void send_one_item(int fd, struct parallel_checkout_item *pc_item) len_data = sizeof(struct pc_item_fixed_portion) + name_len + working_tree_encoding_len; - data = xcalloc(1, len_data); + data = xmalloc(len_data); fixed_portion = (struct pc_item_fixed_portion *)data; fixed_portion->id = pc_item->id; @@ -421,13 +421,12 @@ static void send_one_item(int fd, struct parallel_checkout_item *pc_item) fixed_portion->name_len = name_len; fixed_portion->working_tree_encoding_len = working_tree_encoding_len; /* - * We use hashcpy() instead of oidcpy() because the hash[] positions - * after `the_hash_algo->rawsz` might not be initialized. And Valgrind - * would complain about passing uninitialized bytes to a syscall - * (write(2)). There is no real harm in this case, but the warning could - * hinder the detection of actual errors. + * We pad the unused bytes in the hash array because, otherwise, + * Valgrind would complain about passing uninitialized bytes to a + * write() syscall. The warning doesn't represent any real risk here, + * but it could hinder the detection of actual errors. */ - hashcpy(fixed_portion->oid.hash, pc_item->ce->oid.hash); + oidcpy_with_padding(&fixed_portion->oid, &pc_item->ce->oid); variant = data + sizeof(*fixed_portion); if (working_tree_encoding_len) {
-- 2.30.1