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lib: objagg: Replace zero-length arrays with flexible-array member

PATCH Applied Gustavo A. R. Silva 3 participants 3 messages Feb 11, 2020 – Feb 17, 2020

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Networking Network drivers Library code Objagg
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Gustavo A. R. Silva

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#0 lore raw

PATCH 1/1 lib: objagg: Replace zero-length arrays 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 inadvertenly introduced[3] to the codebase from now on.

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 <[email protected]>
---
 lib/objagg.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)
lib/objagg.c +2 -2
index 576be22e86de..668a2c0a88ac 100644
@@ -28,7 +28,7 @@ struct objagg_hints_node {
 	struct objagg_hints_node *parent;
 	unsigned int root_id;
 	struct objagg_obj_stats_info stats_info;
-	unsigned long obj[0];
+	unsigned long obj[];
 };
 
 static struct objagg_hints_node *

@@ -66,7 +66,7 @@ struct objagg_obj {
 				* including nested objects
 				*/
 	struct objagg_obj_stats stats;
-	unsigned long obj[0];
+	unsigned long obj[];
 };
 
 static unsigned int objagg_obj_ref_inc(struct objagg_obj *objagg_obj)
Signature · 1 line
2.25.0
maintainer Acked-by on v1 1/1
#1 lore raw
Quoted 15 lines · Tue, Feb 11, 2020 at 09:53:56PM CET, [email protected] 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 inadvertenly introduced[3] to the codebase from now on.

Quoted 7 lines

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 <[email protected]>
Acked-by Jiri Pirko <[email protected]>
maintainer Applied
#2 lore raw
In reply to Gustavo A. R. Silva

From: "Gustavo A. R. Silva" <[email protected]>
Date: Tue, 11 Feb 2020 14:53:56 -0600

Quoted 15 lines

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 inadvertenly introduced[3] to the codebase from now on.

Quoted 7 lines

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 <[email protected]>

Applied to net-next.