Messages in this thread Patch in this message | | | Date | Mon, 2 Mar 2020 16:45:01 -0600 | From | "Gustavo A. R. Silva" <> | Subject | [PATCH] gcov: gcc_3_4: 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> --- kernel/gcov/gcc_3_4.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/kernel/gcov/gcc_3_4.c b/kernel/gcov/gcc_3_4.c index 801ee4b0b969..acb83558e5df 100644 --- a/kernel/gcov/gcc_3_4.c +++ b/kernel/gcov/gcc_3_4.c @@ -38,7 +38,7 @@ static struct gcov_info *gcov_info_head; struct gcov_fn_info { unsigned int ident; unsigned int checksum; - unsigned int n_ctrs[0]; + unsigned int n_ctrs[]; }; /** @@ -78,7 +78,7 @@ struct gcov_info { unsigned int n_functions; const struct gcov_fn_info *functions; unsigned int ctr_mask; - struct gcov_ctr_info counts[0]; + struct gcov_ctr_info counts[]; }; /** @@ -352,7 +352,7 @@ struct gcov_iterator { unsigned int count; int num_types; - struct type_info type_info[0]; + struct type_info type_info[]; }; static struct gcov_fn_info *get_func(struct gcov_iterator *iter) -- 2.25.0
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