All of lore.kernel.org
 help / color / mirror / Atom feed
* [PATCH] gcov: gcc_3_4: Replace zero-length array with flexible-array member
@ 2020-03-02 22:45 Gustavo A. R. Silva
  0 siblings, 0 replies; only message in thread
From: Gustavo A. R. Silva @ 2020-03-02 22:45 UTC (permalink / raw)
  To: Peter Oberparleiter, Andrew Morton; +Cc: 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>
---
 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


^ permalink raw reply	[flat|nested] only message in thread

only message in thread, other threads:[~2020-03-02 22:42 UTC | newest]

Thread overview: (only message) (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-03-02 22:45 [PATCH] gcov: gcc_3_4: Replace zero-length array with flexible-array member Gustavo A. R. Silva

This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.