* [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member
@ 2020-02-12 19:52 Gustavo A. R. Silva
2020-02-12 20:49 ` Miguel Ojeda
0 siblings, 1 reply; 5+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-12 19:52 UTC (permalink / raw)
To: Miguel Ojeda Sandonis; +Cc: linux-kernel, Gustavo A. R. Silva
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.
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>
---
drivers/auxdisplay/charlcd.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/auxdisplay/charlcd.c b/drivers/auxdisplay/charlcd.c
index 874c259a8829..c0da3820454b 100644
--- a/drivers/auxdisplay/charlcd.c
+++ b/drivers/auxdisplay/charlcd.c
@@ -88,7 +88,7 @@ struct charlcd_priv {
int len;
} esc_seq;
- unsigned long long drvdata[0];
+ unsigned long long drvdata[];
};
#define charlcd_to_priv(p) container_of(p, struct charlcd_priv, lcd)
--
2.25.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member
2020-02-12 19:52 [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member Gustavo A. R. Silva
@ 2020-02-12 20:49 ` Miguel Ojeda
2020-02-13 6:13 ` Gustavo A. R. Silva
0 siblings, 1 reply; 5+ messages in thread
From: Miguel Ojeda @ 2020-02-12 20:49 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: linux-kernel
Hi Gustavo,
On Wed, Feb 12, 2020 at 8:49 PM Gustavo A. R. Silva
<gustavo@embeddedor.com> 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.
s:inadvertenly:inadvertently:
> 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>
I saw the discussion regarding this -- thanks! Do you want me to
handle this or will you push everything centrally? If the latter, have
my
Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
Cheers,
Miguel
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member
2020-02-12 20:49 ` Miguel Ojeda
@ 2020-02-13 6:13 ` Gustavo A. R. Silva
2020-03-06 21:24 ` Miguel Ojeda
0 siblings, 1 reply; 5+ messages in thread
From: Gustavo A. R. Silva @ 2020-02-13 6:13 UTC (permalink / raw)
To: Miguel Ojeda; +Cc: linux-kernel
Hi Miguel,
On 2/12/20 14:49, Miguel Ojeda wrote:
> Hi Gustavo,
>
> On Wed, Feb 12, 2020 at 8:49 PM Gustavo A. R. Silva
> <gustavo@embeddedor.com> 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.
>
> s:inadvertenly:inadvertently:
>
Thanks for this.
>> 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>
>
> I saw the discussion regarding this -- thanks! Do you want me to
> handle this or will you push everything centrally? If the latter, have
> my
>
Please, go ahead and handle it.
> Acked-by: Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>
>
Thanks
--
Gustavo
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member
2020-02-13 6:13 ` Gustavo A. R. Silva
@ 2020-03-06 21:24 ` Miguel Ojeda
2020-03-07 7:23 ` Gustavo A. R. Silva
0 siblings, 1 reply; 5+ messages in thread
From: Miguel Ojeda @ 2020-03-06 21:24 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: linux-kernel
Hi Gustavo,
On Thu, Feb 13, 2020 at 7:11 AM Gustavo A. R. Silva
<gustavo@embeddedor.com> wrote:
>
> Please, go ahead and handle it.
Picking it up for next week!
Cheers,
Miguel
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member
2020-03-06 21:24 ` Miguel Ojeda
@ 2020-03-07 7:23 ` Gustavo A. R. Silva
0 siblings, 0 replies; 5+ messages in thread
From: Gustavo A. R. Silva @ 2020-03-07 7:23 UTC (permalink / raw)
To: Miguel Ojeda; +Cc: linux-kernel
Hi Miguel,
On 3/6/20 15:24, Miguel Ojeda wrote:
> Hi Gustavo,
>
> On Thu, Feb 13, 2020 at 7:11 AM Gustavo A. R. Silva
> <gustavo@embeddedor.com> wrote:
>>
>> Please, go ahead and handle it.
>
> Picking it up for next week!
>
Awesome. :)
Thank you
--
Gustavo
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2020-03-07 7:20 UTC | newest]
Thread overview: 5+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-02-12 19:52 [PATCH] auxdisplay: charlcd: replace zero-length array with flexible-array member Gustavo A. R. Silva
2020-02-12 20:49 ` Miguel Ojeda
2020-02-13 6:13 ` Gustavo A. R. Silva
2020-03-06 21:24 ` Miguel Ojeda
2020-03-07 7:23 ` Gustavo A. R. Silva
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).