Messages in this thread | | | Subject | Re: [PATCH][next] ocfs2: dlm: Replace zero-length array with flexible-array member | From | Joseph Qi <> | Date | Tue, 10 Mar 2020 09:07:21 +0800 |
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On 2020/3/10 04:20, Gustavo A. R. Silva wrote: > 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>
Acked-by: Joseph Qi <joseph.qi@linux.alibaba.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) > >
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