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prism54: Replace zero-length array with flexible-array

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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]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

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 <gustavoars@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200507190210.GA15375@embeddedor
This commit is contained in:
Gustavo A. R. Silva 2020-05-07 14:02:10 -05:00 committed by Kalle Valo
parent 174812346c
commit 8d7d7a93d5
2 changed files with 5 additions and 5 deletions
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8
drivers/net/wireless/intersil/prism54/isl_oid.h
View file

@ -37,7 +37,7 @@ struct obj_mlmeex {
u16 state;
u16 code;
u16 size;
u8 data[0];
u8 data[];
} __packed;
struct obj_buffer {
@ -68,12 +68,12 @@ struct obj_bss {
struct obj_bsslist {
u32 nr;
struct obj_bss bsslist[0];
struct obj_bss bsslist[];
} __packed;
struct obj_frequencies {
u16 nr;
u16 mhz[0];
u16 mhz[];
} __packed;
struct obj_attachment {
@ -81,7 +81,7 @@ struct obj_attachment {
char reserved;
short id;
short size;
char data[0];
char data[];
} __packed;
/*

2
drivers/net/wireless/intersil/prism54/islpci_mgt.h
View file

@ -99,7 +99,7 @@ struct islpci_mgmtframe {
pimfor_header_t *header; /* payload header, points into buf */
void *data; /* payload ex header, points into buf */
struct work_struct ws; /* argument for schedule_work() */
char buf[0]; /* fragment buffer */
char buf[]; /* fragment buffer */
};
int