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SubjectRe: [PATCH AUTOSEL 5.5 456/542] char: hpet: Use flexible-array member
On Fri, Feb 14, 2020 at 10:47:28AM -0500, Sasha Levin wrote:
> From: "Gustavo A. R. Silva" <gustavo@embeddedor.com>
>
> [ Upstream commit 987f028b8637cfa7658aa456ae73f8f21a7a7f6f ]
>
> Old code in the kernel uses 1-byte and 0-byte arrays to indicate the
> presence of a "variable length array":
>
> struct something {
> int length;
> u8 data[1];
> };
>
> struct something *instance;
>
> instance = kmalloc(sizeof(*instance) + size, GFP_KERNEL);
> instance->length = size;
> memcpy(instance->data, source, size);
>
> There is also 0-byte arrays. Both cases pose confusion for things like
> sizeof(), CONFIG_FORTIFY_SOURCE, etc.[1] Instead, the preferred mechanism
> to declare variable-length types such as the one above is a flexible array
> member[2] which need to be the last member of a structure and empty-sized:
>
> struct something {
> int stuff;
> u8 data[];
> };
>
> Also, 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
> unadvertenly introduced[3] to the codebase from now on.
>
> [1] https://github.com/KSPP/linux/issues/21
> [2] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
> [3] commit 76497732932f ("cxgb3/l2t: Fix undefined behaviour")
>
> Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
> Link: https://lore.kernel.org/r/20200120235326.GA29231@embeddedor.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Signed-off-by: Sasha Levin <sashal@kernel.org>
> ---
> drivers/char/hpet.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/char/hpet.c b/drivers/char/hpet.c
> index 9ac6671bb5141..aed2c45f7968c 100644
> --- a/drivers/char/hpet.c
> +++ b/drivers/char/hpet.c
> @@ -110,7 +110,7 @@ struct hpets {
> unsigned long hp_delta;
> unsigned int hp_ntimer;
> unsigned int hp_which;
> - struct hpet_dev hp_dev[1];
> + struct hpet_dev hp_dev[];
> };
>
> static struct hpets *hpets;
> --
> 2.20.1
>

Not needed, please drop from all trees. Along with the other hpet patch
that fixes the bug this one introduced :)

thanks,

greg k-h

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