* [PATCH] i2c: mux: Replace zero-length array with flexible-array
@ 2020-05-07 18:53 Gustavo A. R. Silva
2020-05-07 22:45 ` Peter Rosin
2020-05-12 10:43 ` Wolfram Sang
0 siblings, 2 replies; 5+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-07 18:53 UTC (permalink / raw)
To: Peter Rosin; +Cc: linux-i2c, 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/i2c-mux.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/include/linux/i2c-mux.h b/include/linux/i2c-mux.h
index c5a977320f82..98ef73b7c8fd 100644
--- a/include/linux/i2c-mux.h
+++ b/include/linux/i2c-mux.h
@@ -29,7 +29,7 @@ struct i2c_mux_core {
int num_adapters;
int max_adapters;
- struct i2c_adapter *adapter[0];
+ struct i2c_adapter *adapter[];
};
struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] i2c: mux: Replace zero-length array with flexible-array
2020-05-07 18:53 [PATCH] i2c: mux: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-07 22:45 ` Peter Rosin
2020-05-12 10:43 ` Wolfram Sang
1 sibling, 0 replies; 5+ messages in thread
From: Peter Rosin @ 2020-05-07 22:45 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: linux-i2c, linux-kernel
On 2020-05-07 20:53, 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
Reviewed-by: Peter Rosin <peda@axentia.se>
Cheers,
Peter
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] i2c: mux: Replace zero-length array with flexible-array
2020-05-07 18:53 [PATCH] i2c: mux: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-07 22:45 ` Peter Rosin
@ 2020-05-12 10:43 ` Wolfram Sang
2020-05-12 23:12 ` Gustavo A. R. Silva
1 sibling, 1 reply; 5+ messages in thread
From: Wolfram Sang @ 2020-05-12 10:43 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: Peter Rosin, linux-i2c, linux-kernel
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On Thu, May 07, 2020 at 01:53:29PM -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 to for-next, thanks! Gustavo, let me know if you think it should
be in for-current.
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^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] i2c: mux: Replace zero-length array with flexible-array
2020-05-12 10:43 ` Wolfram Sang
@ 2020-05-12 23:12 ` Gustavo A. R. Silva
2020-05-13 10:37 ` Wolfram Sang
0 siblings, 1 reply; 5+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-12 23:12 UTC (permalink / raw)
To: Wolfram Sang; +Cc: Peter Rosin, linux-i2c, linux-kernel
On Tue, May 12, 2020 at 12:43:19PM +0200, Wolfram Sang wrote:
> >
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>
> Applied to for-next, thanks! Gustavo, let me know if you think it should
> be in for-current.
>
Hi Wolfram,
If that's not much work for you, then it'd be great if you include
it for 5.7. :)
Thanks
--
Gustavo
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] i2c: mux: Replace zero-length array with flexible-array
2020-05-12 23:12 ` Gustavo A. R. Silva
@ 2020-05-13 10:37 ` Wolfram Sang
0 siblings, 0 replies; 5+ messages in thread
From: Wolfram Sang @ 2020-05-13 10:37 UTC (permalink / raw)
To: Gustavo A. R. Silva; +Cc: Peter Rosin, linux-i2c, linux-kernel
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> If that's not much work for you, then it'd be great if you include
> it for 5.7. :)
No problem, done now!
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^ permalink raw reply [flat|nested] 5+ messages in thread
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2020-05-07 18:53 [PATCH] i2c: mux: Replace zero-length array with flexible-array Gustavo A. R. Silva
2020-05-07 22:45 ` Peter Rosin
2020-05-12 10:43 ` Wolfram Sang
2020-05-12 23:12 ` Gustavo A. R. Silva
2020-05-13 10:37 ` Wolfram Sang
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