From: "Gustavo A. R. Silva" <gustavoars@kernel.org>
To: Jeff Dike <jdike@addtoit.com>,
Richard Weinberger <richard@nod.at>,
Anton Ivanov <anton.ivanov@cambridgegreys.com>
Cc: linux-um@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: [PATCH] um: virtio: Replace zero-length array with flexible-array
Date: Thu, 7 May 2020 14:26:52 -0500 [thread overview]
Message-ID: <20200507192652.GA16743@embeddedor> (raw)
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:
struct foo {
int stuff;
struct boo array[];
};
By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.
Also, notice that, dynamic memory allocations won't be affected by
this change:
"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]
sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.
This issue was found with the help of Coccinelle.
[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
arch/um/drivers/vector_kern.h | 2 +-
arch/um/drivers/vhost_user.h | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/um/drivers/vector_kern.h b/arch/um/drivers/vector_kern.h
index d0159082faf0..8fff93a75a92 100644
--- a/arch/um/drivers/vector_kern.h
+++ b/arch/um/drivers/vector_kern.h
@@ -129,7 +129,7 @@ struct vector_private {
struct vector_estats estats;
struct sock_fprog *bpf;
- char user[0];
+ char user[];
};
extern int build_transport_data(struct vector_private *vp);
diff --git a/arch/um/drivers/vhost_user.h b/arch/um/drivers/vhost_user.h
index 6c71b6005177..6f147cd3c9f7 100644
--- a/arch/um/drivers/vhost_user.h
+++ b/arch/um/drivers/vhost_user.h
@@ -78,7 +78,7 @@ struct vhost_user_config {
u32 offset;
u32 size;
u32 flags;
- u8 payload[0]; /* Variable length */
+ u8 payload[]; /* Variable length */
} __packed;
struct vhost_user_vring_state {
reply other threads:[~2020-05-07 19:22 UTC|newest]
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