Linux-NVME Archive on lore.kernel.org
 help / color / Atom feed
* [PATCH] nvme: Replace zero-length array with flexible-array member
@ 2020-02-26 21:16 Gustavo A. R. Silva
  0 siblings, 0 replies; only message in thread
From: Gustavo A. R. Silva @ 2020-02-26 21:16 UTC (permalink / raw)
  To: James Smart, Keith Busch, Jens Axboe, Christoph Hellwig, Sagi Grimberg
  Cc: linux-kernel, linux-nvme, Gustavo A. R. Silva

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]

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 <gustavo@embeddedor.com>
---
 drivers/nvme/host/fc.c       | 2 +-
 drivers/nvme/host/lightnvm.c | 2 +-
 include/linux/nvme.h         | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/nvme/host/fc.c b/drivers/nvme/host/fc.c
index 5a70ac395d53..6806a19707fb 100644
--- a/drivers/nvme/host/fc.c
+++ b/drivers/nvme/host/fc.c
@@ -96,7 +96,7 @@ struct nvme_fc_fcp_op {
 struct nvme_fcp_op_w_sgl {
 	struct nvme_fc_fcp_op	op;
 	struct scatterlist	sgl[NVME_INLINE_SG_CNT];
-	uint8_t			priv[0];
+	uint8_t			priv[];
 };
 
 struct nvme_fc_lport {
diff --git a/drivers/nvme/host/lightnvm.c b/drivers/nvme/host/lightnvm.c
index ec46693f6b64..3002bf972c6b 100644
--- a/drivers/nvme/host/lightnvm.c
+++ b/drivers/nvme/host/lightnvm.c
@@ -171,7 +171,7 @@ struct nvme_nvm_bb_tbl {
 	__le32	tdresv;
 	__le32	thresv;
 	__le32	rsvd2[8];
-	__u8	blk[0];
+	__u8	blk[];
 };
 
 struct nvme_nvm_id20_addrf {
diff --git a/include/linux/nvme.h b/include/linux/nvme.h
index 3d5189f46cb1..6ee80a44ed4f 100644
--- a/include/linux/nvme.h
+++ b/include/linux/nvme.h
@@ -1177,7 +1177,7 @@ struct nvmf_disc_rsp_page_hdr {
 	__le64		numrec;
 	__le16		recfmt;
 	__u8		resv14[1006];
-	struct nvmf_disc_rsp_page_entry entries[0];
+	struct nvmf_disc_rsp_page_entry entries[];
 };
 
 enum {
-- 
2.25.0


_______________________________________________
linux-nvme mailing list
linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme

^ permalink raw reply	[flat|nested] only message in thread

only message in thread, back to index

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-26 21:16 [PATCH] nvme: Replace zero-length array with flexible-array member Gustavo A. R. Silva

Linux-NVME Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-nvme/0 linux-nvme/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-nvme linux-nvme/ https://lore.kernel.org/linux-nvme \
		linux-nvme@lists.infradead.org
	public-inbox-index linux-nvme

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.infradead.lists.linux-nvme


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git