* [PATCH][next] f2fs: xattr.h: Replace zero-length array with flexible-array member
@ 2020-03-09 18:10 ` Gustavo A. R. Silva
0 siblings, 0 replies; 4+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-09 18:10 UTC (permalink / raw)
To: Jaegeuk Kim, Chao Yu; +Cc: linux-f2fs-devel, linux-kernel, 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>
---
fs/f2fs/xattr.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/f2fs/xattr.h b/fs/f2fs/xattr.h
index de0c600b9cab..95d589bf8e22 100644
--- a/fs/f2fs/xattr.h
+++ b/fs/f2fs/xattr.h
@@ -49,7 +49,7 @@ struct f2fs_xattr_entry {
__u8 e_name_index;
__u8 e_name_len;
__le16 e_value_size; /* size of attribute value */
- char e_name[0]; /* attribute name */
+ char e_name[]; /* attribute name */
};
#define XATTR_HDR(ptr) ((struct f2fs_xattr_header *)(ptr))
--
2.25.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* [f2fs-dev] [PATCH][next] f2fs: xattr.h: Replace zero-length array with flexible-array member
@ 2020-03-09 18:10 ` Gustavo A. R. Silva
0 siblings, 0 replies; 4+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-09 18:10 UTC (permalink / raw)
To: Jaegeuk Kim, Chao Yu; +Cc: Gustavo A. R. Silva, linux-kernel, linux-f2fs-devel
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/f2fs/xattr.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/f2fs/xattr.h b/fs/f2fs/xattr.h
index de0c600b9cab..95d589bf8e22 100644
--- a/fs/f2fs/xattr.h
+++ b/fs/f2fs/xattr.h
@@ -49,7 +49,7 @@ struct f2fs_xattr_entry {
__u8 e_name_index;
__u8 e_name_len;
__le16 e_value_size; /* size of attribute value */
- char e_name[0]; /* attribute name */
+ char e_name[]; /* attribute name */
};
#define XATTR_HDR(ptr) ((struct f2fs_xattr_header *)(ptr))
--
2.25.0
_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [f2fs-dev] [PATCH][next] f2fs: xattr.h: Replace zero-length array with flexible-array member
2020-03-09 18:10 ` [f2fs-dev] " Gustavo A. R. Silva
@ 2020-03-12 1:07 ` Chao Yu
-1 siblings, 0 replies; 4+ messages in thread
From: Chao Yu @ 2020-03-12 1:07 UTC (permalink / raw)
To: Gustavo A. R. Silva, Jaegeuk Kim, Chao Yu; +Cc: linux-kernel, linux-f2fs-devel
On 2020/3/10 2:10, 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>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Thanks,
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [f2fs-dev] [PATCH][next] f2fs: xattr.h: Replace zero-length array with flexible-array member
@ 2020-03-12 1:07 ` Chao Yu
0 siblings, 0 replies; 4+ messages in thread
From: Chao Yu @ 2020-03-12 1:07 UTC (permalink / raw)
To: Gustavo A. R. Silva, Jaegeuk Kim, Chao Yu; +Cc: linux-kernel, linux-f2fs-devel
On 2020/3/10 2:10, 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>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Thanks,
_______________________________________________
Linux-f2fs-devel mailing list
Linux-f2fs-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2020-03-12 1:07 UTC | newest]
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2020-03-09 18:10 [PATCH][next] f2fs: xattr.h: Replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-03-09 18:10 ` [f2fs-dev] " Gustavo A. R. Silva
2020-03-12 1:07 ` Chao Yu
2020-03-12 1:07 ` Chao Yu
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