diff options
author | Matheus Tavares <matheus.bernardino@usp.br> | 2021-05-17 16:49:03 -0300 |
---|---|---|
committer | Junio C Hamano <gitster@pobox.com> | 2021-05-18 05:38:54 +0900 |
commit | 3d20ed27b8bdac5c82f4f78af802f9afa499f651 (patch) | |
tree | 4ac43f95e03a611d9e87630d9616d27cec0eefff | |
parent | bf949ade81106fbda068c1fdb2c6fd1cb1babe7e (diff) | |
download | git-3d20ed27b8bdac5c82f4f78af802f9afa499f651.tar.gz |
parallel-checkout: send the new object_id algo field to the workers
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>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
-rw-r--r-- | hash.h | 16 | ||||
-rw-r--r-- | parallel-checkout.c | 13 |
2 files changed, 22 insertions, 7 deletions
@@ -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) { |