From a6b9832e495be636bcccf25e0aebdeb564addf06 Mon Sep 17 00:00:00 2001
From: Laurent Vivier <lvivier@redhat.com>
Date: Tue, 13 May 2025 11:41:00 +0200
Subject: [PATCH] virtio: Fix Clang warning (bugprone-sizeof-expression,
cert-arr39-c)
In `virtqueue_read_indirect_desc()`, the pointer arithmetic involving
`desc` is intentional. We add the length in bytes (`read_len`)
divided by the size of `struct vring_desc` to `desc`, which is
an array of `struct vring_desc`. This correctly calculates the
offset in terms of the number of `struct vring_desc` elements.
Clang issues the following warning due to this explicit scaling:
virtio.c:238:8: error: suspicious usage of 'sizeof(...)' in pointer
arithmetic; this scaled value will be scaled again by the '+='
operator [bugprone-sizeof-expression,cert-arr39-c,-Werror]
238 | desc += read_len / sizeof(struct vring_desc);
| ^ ~~~~~~~~~~~~~~~~~~~~~~~~~
virtio.c:238:8: note: '+=' in pointer arithmetic internally scales
with 'sizeof(struct vring_desc)' == 16
This behavior is intended, so the warning can be considered a
false positive in this context. The code correctly advances the
pointer by the desired number of descriptor entries.
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
---
virtio.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/virtio.c b/virtio.c
index bc2b89a..f7db007 100644
--- a/virtio.c
+++ b/virtio.c
@@ -235,6 +235,7 @@ static int virtqueue_read_indirect_desc(const struct vu_dev *dev,
memcpy(desc, orig_desc, read_len);
len -= read_len;
addr += read_len;
+ /* NOLINTNEXTLINE(bugprone-sizeof-expression,cert-arr39-c) */
desc += read_len / sizeof(struct vring_desc);
}