* [PATCH] thunderbolt: Replace zero-length array with flexible-array
@ 2020-05-07 19:25 Gustavo A. R. Silva
2020-05-11 10:34 ` Mika Westerberg
0 siblings, 1 reply; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-07 19:25 UTC (permalink / raw)
To: Andreas Noever, Michael Jamet, Mika Westerberg, Yehezkel Bernat
Cc: linux-usb, 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>
---
include/linux/thunderbolt.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/thunderbolt.h b/include/linux/thunderbolt.h
index ece782ef5466..ff397c0d5c07 100644
--- a/include/linux/thunderbolt.h
+++ b/include/linux/thunderbolt.h
@@ -80,7 +80,7 @@ struct tb {
int index;
enum tb_security_level security_level;
size_t nboot_acl;
- unsigned long privdata[0];
+ unsigned long privdata[];
};
extern struct bus_type tb_bus_type;
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] thunderbolt: Replace zero-length array with flexible-array
2020-05-07 19:25 [PATCH] thunderbolt: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-11 10:34 ` Mika Westerberg
2020-05-12 18:12 ` Gustavo A. R. Silva
0 siblings, 1 reply; 3+ messages in thread
From: Mika Westerberg @ 2020-05-11 10:34 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Andreas Noever, Michael Jamet, Yehezkel Bernat, linux-usb, linux-kernel
On Thu, May 07, 2020 at 02:25:24PM -0500, Gustavo A. R. Silva 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>
Applied, thanks!
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] thunderbolt: Replace zero-length array with flexible-array
2020-05-11 10:34 ` Mika Westerberg
@ 2020-05-12 18:12 ` Gustavo A. R. Silva
0 siblings, 0 replies; 3+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-12 18:12 UTC (permalink / raw)
To: Mika Westerberg
Cc: Andreas Noever, Michael Jamet, Yehezkel Bernat, linux-usb, linux-kernel
On Mon, May 11, 2020 at 01:34:15PM +0300, Mika Westerberg wrote:
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>
> Applied, thanks!
Thanks, Mika.
--
Gustavo
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-05-07 19:25 [PATCH] thunderbolt: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-11 10:34 ` Mika Westerberg
2020-05-12 18:12 ` Gustavo A. R. Silva
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