From a4e439a6f628a52f7074c9d73ec7eb4f6c1a4dfc Mon Sep 17 00:00:00 2001 From: "Gustavo A. R. Silva" Date: Mon, 9 Mar 2020 10:56:08 -0500 Subject: [PATCH] dlm: dlm_internal: Replace zero-length array with flexible-array member 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 Signed-off-by: David Teigland --- fs/dlm/dlm_internal.h | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/fs/dlm/dlm_internal.h b/fs/dlm/dlm_internal.h index 416d9de35679..d231ae5d2c65 100644 --- a/fs/dlm/dlm_internal.h +++ b/fs/dlm/dlm_internal.h @@ -421,7 +421,7 @@ struct dlm_message { int m_bastmode; int m_asts; int m_result; /* 0 or -EXXX */ - char m_extra[0]; /* name or lvb */ + char m_extra[]; /* name or lvb */ }; @@ -450,7 +450,7 @@ struct dlm_rcom { uint64_t rc_id; /* match reply with request */ uint64_t rc_seq; /* sender's ls_recover_seq */ uint64_t rc_seq_reply; /* remote ls_recover_seq */ - char rc_buf[0]; + char rc_buf[]; }; union dlm_packet { @@ -506,7 +506,7 @@ struct rcom_lock { __le16 rl_wait_type; __le16 rl_namelen; char rl_name[DLM_RESNAME_MAXLEN]; - char rl_lvb[0]; + char rl_lvb[]; }; /*