* [PATCH] PNPBIOS: Replace zero-length array with flexible-array
@ 2020-05-07 19:06 Gustavo A. R. Silva
2020-05-15 16:23 ` Rafael J. Wysocki
0 siblings, 1 reply; 2+ messages in thread
From: Gustavo A. R. Silva @ 2020-05-07 19:06 UTC (permalink / raw)
To: Rafael J. Wysocki; +Cc: linux-acpi, 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/pnp/pnpbios/pnpbios.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/pnp/pnpbios/pnpbios.h b/drivers/pnp/pnpbios/pnpbios.h
index 37acb8378f39..2ce739ff9c1a 100644
--- a/drivers/pnp/pnpbios/pnpbios.h
+++ b/drivers/pnp/pnpbios/pnpbios.h
@@ -107,7 +107,7 @@ struct pnp_bios_node {
__u32 eisa_id;
__u8 type_code[3];
__u16 flags;
- __u8 data[0];
+ __u8 data[];
};
#pragma pack()
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] PNPBIOS: Replace zero-length array with flexible-array
2020-05-07 19:06 [PATCH] PNPBIOS: Replace zero-length array with flexible-array Gustavo A. R. Silva
@ 2020-05-15 16:23 ` Rafael J. Wysocki
0 siblings, 0 replies; 2+ messages in thread
From: Rafael J. Wysocki @ 2020-05-15 16:23 UTC (permalink / raw)
To: Gustavo A. R. Silva
Cc: Rafael J. Wysocki, ACPI Devel Maling List, Linux Kernel Mailing List
On Thu, May 7, 2020 at 9:02 PM 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>
> ---
> drivers/pnp/pnpbios/pnpbios.h | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/pnp/pnpbios/pnpbios.h b/drivers/pnp/pnpbios/pnpbios.h
> index 37acb8378f39..2ce739ff9c1a 100644
> --- a/drivers/pnp/pnpbios/pnpbios.h
> +++ b/drivers/pnp/pnpbios/pnpbios.h
> @@ -107,7 +107,7 @@ struct pnp_bios_node {
> __u32 eisa_id;
> __u8 type_code[3];
> __u16 flags;
> - __u8 data[0];
> + __u8 data[];
> };
> #pragma pack()
Applied as 5.8 material, thanks!
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2020-05-15 16:23 ` Rafael J. Wysocki
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