* [PATCH] prism54: Replace zero-length array with flexible-array
@ 2020-05-07 19:02 Gustavo A. R. Silva
2020-05-12 8:56 ` Kalle Valo
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-07 19:02 UTC (permalink / raw)
To: Kalle Valo; +Cc: linux-wireless, linux-kernel
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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
---
drivers/net/wireless/intersil/prism54/isl_oid.h | 8 ++++----
drivers/net/wireless/intersil/prism54/islpci_mgt.h | 2 +-
2 files changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/net/wireless/intersil/prism54/isl_oid.h b/drivers/net/wireless/intersil/prism54/isl_oid.h
index 5441c1f9f2fc..1afc2ccf94ca 100644
--- a/drivers/net/wireless/intersil/prism54/isl_oid.h
+++ b/drivers/net/wireless/intersil/prism54/isl_oid.h
@@ -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;
/*
diff --git a/drivers/net/wireless/intersil/prism54/islpci_mgt.h b/drivers/net/wireless/intersil/prism54/islpci_mgt.h
index d6bbbac46b4a..1f87d0aea60c 100644
--- a/drivers/net/wireless/intersil/prism54/islpci_mgt.h
+++ b/drivers/net/wireless/intersil/prism54/islpci_mgt.h
@@ -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
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] prism54: Replace zero-length array with flexible-array
2020-05-07 19:02 [PATCH] prism54: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-12 8:56 ` Kalle Valo
0 siblings, 0 replies; 2+ messages in thread
From: Kalle Valo @ 2020-05-12 8:56 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: linux-wireless, linux-kernel
"Gustavo A. R. Silva" <gustavoars@kernel.org> 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
> 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 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Patch applied to wireless-drivers-next.git, thanks.
8d7d7a93d526 prism54: Replace zero-length array with flexible-array
--
https://patchwork.kernel.org/patch/11534747/
https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches
^ permalink raw reply [flat|nested] 2+ messages in thread
end of thread, other threads:[~2020-05-12 8:56 UTC | newest]
Thread overview: 2+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-05-07 19:02 [PATCH] prism54: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-12 8:56 ` Kalle Valo
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).