Messages in this thread Patch in this message | | | Date | Mon, 9 Mar 2020 15:20:16 -0500 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH][next] ocfs2: dlm: Replace zero-length array with flexible-array member |
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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> --- fs/ocfs2/dlm/dlmcommon.h | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)
diff --git a/fs/ocfs2/dlm/dlmcommon.h b/fs/ocfs2/dlm/dlmcommon.h index 0463dce65bb2..c8a444622faa 100644 --- a/fs/ocfs2/dlm/dlmcommon.h +++ b/fs/ocfs2/dlm/dlmcommon.h @@ -564,7 +564,7 @@ struct dlm_migratable_lockres // 48 bytes u8 lvb[DLM_LVB_LEN]; // 112 bytes - struct dlm_migratable_lock ml[0]; // 16 bytes each, begins at byte 112 + struct dlm_migratable_lock ml[]; // 16 bytes each, begins at byte 112 }; #define DLM_MIG_LOCKRES_MAX_LEN \ (sizeof(struct dlm_migratable_lockres) + \ @@ -601,7 +601,7 @@ struct dlm_convert_lock u8 name[O2NM_MAX_NAME_LEN]; - s8 lvb[0]; + s8 lvb[]; }; #define DLM_CONVERT_LOCK_MAX_LEN (sizeof(struct dlm_convert_lock)+DLM_LVB_LEN) @@ -616,7 +616,7 @@ struct dlm_unlock_lock u8 name[O2NM_MAX_NAME_LEN]; - s8 lvb[0]; + s8 lvb[]; }; #define DLM_UNLOCK_LOCK_MAX_LEN (sizeof(struct dlm_unlock_lock)+DLM_LVB_LEN) @@ -632,7 +632,7 @@ struct dlm_proxy_ast u8 name[O2NM_MAX_NAME_LEN]; - s8 lvb[0]; + s8 lvb[]; }; #define DLM_PROXY_AST_MAX_LEN (sizeof(struct dlm_proxy_ast)+DLM_LVB_LEN) -- 2.25.0
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