Messages in this thread Patch in this message | | | Date | Mon, 9 Mar 2020 15:24:49 -0500 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH][next] fs: select: 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/select.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/fs/select.c b/fs/select.c index 11d0285d46b7..f38a8a7480f7 100644 --- a/fs/select.c +++ b/fs/select.c @@ -97,7 +97,7 @@ u64 select_estimate_accuracy(struct timespec64 *tv) struct poll_table_page { struct poll_table_page * next; struct poll_table_entry * entry; - struct poll_table_entry entries[0]; + struct poll_table_entry entries[]; }; #define POLL_TABLE_FULL(table) \ @@ -826,7 +826,7 @@ SYSCALL_DEFINE1(old_select, struct sel_arg_struct __user *, arg) struct poll_list { struct poll_list *next; int len; - struct pollfd entries[0]; + struct pollfd entries[]; }; #define POLLFD_PER_PAGE ((PAGE_SIZE-sizeof(struct poll_list)) / sizeof(struct pollfd)) -- 2.25.0
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