[148/166] gcov: gcc_3_4: replace zero-length array with flexible-array member
diff mbox series

Message ID 20200407031155.sjtwHB7DK%akpm@linux-foundation.org
State New
Headers show
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Commit Message

Andrew Morton April 7, 2020, 3:11 a.m. UTC
From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
Subject: gcov: gcc_3_4: 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

"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")

Link: http://lkml.kernel.org/r/20200302224501.GA14175@embeddedor
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Cc: Peter Oberparleiter <oberpar@linux.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

 kernel/gcov/gcc_3_4.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff mbox series

--- a/kernel/gcov/gcc_3_4.c~gcov-gcc_3_4-replace-zero-length-array-with-flexible-array-member
+++ a/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)