Gustavo A. R. Silva
2020-Mar-09 20:21 UTC
[Ocfs2-devel] [PATCH][next] ocfs2: ocfs2_fs.h: 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!OKPotRhYhHbCG2kibo8Q6_6CuKaa28d_74h1svxyR6rbshrK2L_BdrQpNbvJWBWb40QCkg$
[2]
https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!OKPotRhYhHbCG2kibo8Q6_6CuKaa28d_74h1svxyR6rbshrK2L_BdrQpNbvJWBUhNn9M6g$
[3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>
---
fs/ocfs2/ocfs2_fs.h | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)
diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h
index 0db4a7ec58a2..0dd8c41bafd4 100644
--- a/fs/ocfs2/ocfs2_fs.h
+++ b/fs/ocfs2/ocfs2_fs.h
@@ -470,7 +470,7 @@ struct ocfs2_extent_list {
__le16 l_reserved1;
__le64 l_reserved2; /* Pad to
sizeof(ocfs2_extent_rec) */
-/*10*/ struct ocfs2_extent_rec l_recs[0]; /* Extent records */
+/*10*/ struct ocfs2_extent_rec l_recs[]; /* Extent records */
};
/*
@@ -484,7 +484,7 @@ struct ocfs2_chain_list {
__le16 cl_count; /* Total chains in this list */
__le16 cl_next_free_rec; /* Next unused chain slot */
__le64 cl_reserved1;
-/*10*/ struct ocfs2_chain_rec cl_recs[0]; /* Chain records */
+/*10*/ struct ocfs2_chain_rec cl_recs[]; /* Chain records */
};
/*
@@ -496,7 +496,7 @@ struct ocfs2_truncate_log {
/*00*/ __le16 tl_count; /* Total records in this log */
__le16 tl_used; /* Number of records in use */
__le32 tl_reserved1;
-/*08*/ struct ocfs2_truncate_rec tl_recs[0]; /* Truncate records */
+/*08*/ struct ocfs2_truncate_rec tl_recs[]; /* Truncate records */
};
/*
@@ -640,7 +640,7 @@ struct ocfs2_local_alloc
__le16 la_size; /* Size of included bitmap, in bytes */
__le16 la_reserved1;
__le64 la_reserved2;
-/*10*/ __u8 la_bitmap[0];
+/*10*/ __u8 la_bitmap[];
};
/*
@@ -653,7 +653,7 @@ struct ocfs2_inline_data
* for data, starting at id_data */
__le16 id_reserved0;
__le32 id_reserved1;
- __u8 id_data[0]; /* Start of user data */
+ __u8 id_data[]; /* Start of user data */
};
/*
@@ -798,7 +798,7 @@ struct ocfs2_dx_entry_list {
* possible in de_entries */
__le16 de_num_used; /* Current number of
* de_entries entries */
- struct ocfs2_dx_entry de_entries[0]; /* Indexed dir entries
+ struct ocfs2_dx_entry de_entries[]; /* Indexed dir entries
* in a packed array of
* length de_num_used */
};
@@ -935,7 +935,7 @@ struct ocfs2_refcount_list {
__le16 rl_used; /* Current number of used records */
__le32 rl_reserved2;
__le64 rl_reserved1; /* Pad to sizeof(ocfs2_refcount_record) */
-/*10*/ struct ocfs2_refcount_rec rl_recs[0]; /* Refcount records */
+/*10*/ struct ocfs2_refcount_rec rl_recs[]; /* Refcount records */
};
@@ -1021,7 +1021,7 @@ struct ocfs2_xattr_header {
buckets. A block uses
xb_check and sets
this field to zero.) */
- struct ocfs2_xattr_entry xh_entries[0]; /* xattr entry list. */
+ struct ocfs2_xattr_entry xh_entries[]; /* xattr entry list. */
};
/*
@@ -1207,7 +1207,7 @@ struct ocfs2_local_disk_dqinfo {
/* Header of one chunk of a quota file */
struct ocfs2_local_disk_chunk {
__le32 dqc_free; /* Number of free entries in the bitmap */
- __u8 dqc_bitmap[0]; /* Bitmap of entries in the corresponding
+ __u8 dqc_bitmap[]; /* Bitmap of entries in the corresponding
* chunk of quota file */
};
--
2.25.0
Joseph Qi
2020-Mar-10 01:07 UTC
[Ocfs2-devel] [PATCH][next] ocfs2: ocfs2_fs.h: Replace zero-length array with flexible-array member
On 2020/3/10 04:21, 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://urldefense.com/v3/__https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html__;!!GqivPVa7Brio!JTw1NYKmjtcAGIuR1tXUzdiVuY3gSXbPJ7RUiTDWFqVfZxM6GVzAejGpyplPNEMo000aCg$ > [2] https://urldefense.com/v3/__https://github.com/KSPP/linux/issues/21__;!!GqivPVa7Brio!JTw1NYKmjtcAGIuR1tXUzdiVuY3gSXbPJ7RUiTDWFqVfZxM6GVzAejGpyplPNENIcqEuAA$ > [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour") > > Signed-off-by: Gustavo A. R. Silva <gustavo at embeddedor.com>Acked-by: Joseph Qi <joseph.qi at linux.alibaba.com>> --- > fs/ocfs2/ocfs2_fs.h | 18 +++++++++--------- > 1 file changed, 9 insertions(+), 9 deletions(-) > > diff --git a/fs/ocfs2/ocfs2_fs.h b/fs/ocfs2/ocfs2_fs.h > index 0db4a7ec58a2..0dd8c41bafd4 100644 > --- a/fs/ocfs2/ocfs2_fs.h > +++ b/fs/ocfs2/ocfs2_fs.h > @@ -470,7 +470,7 @@ struct ocfs2_extent_list { > __le16 l_reserved1; > __le64 l_reserved2; /* Pad to > sizeof(ocfs2_extent_rec) */ > -/*10*/ struct ocfs2_extent_rec l_recs[0]; /* Extent records */ > +/*10*/ struct ocfs2_extent_rec l_recs[]; /* Extent records */ > }; > > /* > @@ -484,7 +484,7 @@ struct ocfs2_chain_list { > __le16 cl_count; /* Total chains in this list */ > __le16 cl_next_free_rec; /* Next unused chain slot */ > __le64 cl_reserved1; > -/*10*/ struct ocfs2_chain_rec cl_recs[0]; /* Chain records */ > +/*10*/ struct ocfs2_chain_rec cl_recs[]; /* Chain records */ > }; > > /* > @@ -496,7 +496,7 @@ struct ocfs2_truncate_log { > /*00*/ __le16 tl_count; /* Total records in this log */ > __le16 tl_used; /* Number of records in use */ > __le32 tl_reserved1; > -/*08*/ struct ocfs2_truncate_rec tl_recs[0]; /* Truncate records */ > +/*08*/ struct ocfs2_truncate_rec tl_recs[]; /* Truncate records */ > }; > > /* > @@ -640,7 +640,7 @@ struct ocfs2_local_alloc > __le16 la_size; /* Size of included bitmap, in bytes */ > __le16 la_reserved1; > __le64 la_reserved2; > -/*10*/ __u8 la_bitmap[0]; > +/*10*/ __u8 la_bitmap[]; > }; > > /* > @@ -653,7 +653,7 @@ struct ocfs2_inline_data > * for data, starting at id_data */ > __le16 id_reserved0; > __le32 id_reserved1; > - __u8 id_data[0]; /* Start of user data */ > + __u8 id_data[]; /* Start of user data */ > }; > > /* > @@ -798,7 +798,7 @@ struct ocfs2_dx_entry_list { > * possible in de_entries */ > __le16 de_num_used; /* Current number of > * de_entries entries */ > - struct ocfs2_dx_entry de_entries[0]; /* Indexed dir entries > + struct ocfs2_dx_entry de_entries[]; /* Indexed dir entries > * in a packed array of > * length de_num_used */ > }; > @@ -935,7 +935,7 @@ struct ocfs2_refcount_list { > __le16 rl_used; /* Current number of used records */ > __le32 rl_reserved2; > __le64 rl_reserved1; /* Pad to sizeof(ocfs2_refcount_record) */ > -/*10*/ struct ocfs2_refcount_rec rl_recs[0]; /* Refcount records */ > +/*10*/ struct ocfs2_refcount_rec rl_recs[]; /* Refcount records */ > }; > > > @@ -1021,7 +1021,7 @@ struct ocfs2_xattr_header { > buckets. A block uses > xb_check and sets > this field to zero.) */ > - struct ocfs2_xattr_entry xh_entries[0]; /* xattr entry list. */ > + struct ocfs2_xattr_entry xh_entries[]; /* xattr entry list. */ > }; > > /* > @@ -1207,7 +1207,7 @@ struct ocfs2_local_disk_dqinfo { > /* Header of one chunk of a quota file */ > struct ocfs2_local_disk_chunk { > __le32 dqc_free; /* Number of free entries in the bitmap */ > - __u8 dqc_bitmap[0]; /* Bitmap of entries in the corresponding > + __u8 dqc_bitmap[]; /* Bitmap of entries in the corresponding > * chunk of quota file */ > }; > >