From 3d20ed27b8bdac5c82f4f78af802f9afa499f651 Mon Sep 17 00:00:00 2001 From: Matheus Tavares Date: Mon, 17 May 2021 16:49:03 -0300 Subject: 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 Signed-off-by: Junio C Hamano --- parallel-checkout.c | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) (limited to 'parallel-checkout.c') 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) { -- cgit v1.2.3