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rio.h: 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 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 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
This commit is contained in:
Gustavo A. R. Silva 2020-03-23 19:12:17 -05:00
parent 70f1451ec9
commit a1c4b9247d
1 changed files with 2 additions and 2 deletions
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4
include/linux/rio.h
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@ -100,7 +100,7 @@ struct rio_switch {
u32 port_ok; u32 port_ok;
struct rio_switch_ops *ops; struct rio_switch_ops *ops;
spinlock_t lock; spinlock_t lock;
struct rio_dev *nextdev[0]; struct rio_dev *nextdev[];
}; };
/** /**
@ -201,7 +201,7 @@ struct rio_dev {
u8 hopcount; u8 hopcount;
struct rio_dev *prev; struct rio_dev *prev;
atomic_t state; atomic_t state;
struct rio_switch rswitch[0]; /* RIO switch info */ struct rio_switch rswitch[]; /* RIO switch info */
}; };
#define rio_dev_g(n) list_entry(n, struct rio_dev, global_list) #define rio_dev_g(n) list_entry(n, struct rio_dev, global_list)