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ethtool.h: 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>
This commit is contained in:
Gustavo A. R. Silva 2020-03-23 17:24:53 -05:00
parent beb69f15a0
commit 5299a11a93
1 changed files with 2 additions and 2 deletions
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4
include/linux/ethtool.h
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@ -35,7 +35,7 @@ struct compat_ethtool_rxnfc {
compat_u64 data; compat_u64 data;
struct compat_ethtool_rx_flow_spec fs; struct compat_ethtool_rx_flow_spec fs;
u32 rule_cnt; u32 rule_cnt;
u32 rule_locs[0]; u32 rule_locs[];
}; };
#endif /* CONFIG_COMPAT */ #endif /* CONFIG_COMPAT */
@ -462,7 +462,7 @@ int ethtool_check_ops(const struct ethtool_ops *ops);
struct ethtool_rx_flow_rule { struct ethtool_rx_flow_rule {
struct flow_rule *rule; struct flow_rule *rule;
unsigned long priv[0]; unsigned long priv[];
}; };
struct ethtool_rx_flow_spec_input { struct ethtool_rx_flow_spec_input {