Re: [PATCH v2] mei: Avoid the use of one-element arrays

Gustavo A. R. Silva
2020-07-22T19:48:41Z

Hi Tomas,

Please, see my comments below...

On 7/22/20 14:04, Winkler, Tomas wrote:
>
>>
>> Hi all,
>>
>> Friendly ping: who can take this? :)
>>
>> Thanks
>> --
>> Gustavo
>>
>> On 7/14/20 16:45, Gustavo A. R. Silva wrote:
>>> One-element arrays are being deprecated[1]. Replace the one-element
>>> arrays with a simple value type u8 reserved, once this is just a
>>> placeholder for alignment.
>>>
>>> Also, while there, use the preferred form for passing a size of a struct.
>>> The alternative form where struct name is spelled out hurts
>>> readability and introduces an opportunity for a bug when the variable
>>> type is changed but the corresponding sizeof that is passed as argument is
>> not.
>>>
>>> [1] https://github.com/KSPP/linux/issues/79
>>>
>>> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
>>> ---
>>> Changes in v2:
>>> - Use a more concise changelog text.
>>>
>>> drivers/misc/mei/hbm.c | 4 ++--
>>> drivers/misc/mei/hw.h | 6 +++---
>>> 2 files changed, 5 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/misc/mei/hbm.c b/drivers/misc/mei/hbm.c index
>>> a44094cdbc36..f020d5594154 100644
>>> --- a/drivers/misc/mei/hbm.c
>>> +++ b/drivers/misc/mei/hbm.c
>>> @@ -408,14 +408,14 @@ static int mei_hbm_add_cl_resp(struct mei_device
>>> *dev, u8 addr, u8 status) {
>>> struct mei_msg_hdr mei_hdr;
>>> struct hbm_add_client_response resp;
>>> - const size_t len = sizeof(struct hbm_add_client_response);
>>> + const size_t len = sizeof(resp);
>>> int ret;
>>>
>>> dev_dbg(dev->dev, "adding client response\n");
>>>
>>> mei_hbm_hdr(&mei_hdr, len);
>>>
>>> - memset(&resp, 0, sizeof(struct hbm_add_client_response));
>>> + memset(&resp, 0, len);
>>> resp.hbm_cmd = MEI_HBM_ADD_CLIENT_RES_CMD;
>>> resp.me_addr = addr;
>>> resp.status = status;
>
> This should be probably in a different patch it's not related to the second part.
>
>>> diff --git a/drivers/misc/mei/hw.h b/drivers/misc/mei/hw.h index
>>> b1a8d5ec88b3..8c0297f0e7f3 100644
>>> --- a/drivers/misc/mei/hw.h
>>> +++ b/drivers/misc/mei/hw.h
> I have second thoughts of this part as all reserved fields in this file are of form u8 reserved[X],
> so we will lose that uniformity with this change, you have to look at the file as whole
> not just at the patch. So I prefer we drop that part of the patch.
>

This is actually the main point of this patch: the removal of one-element arrays.
And yeah, every place in the kernel that uses the form that you mention will see
it's uniformity slightly modified, and that's for a good cause: the removal of
one-element arrays, so we can enable bounds checking.

Thanks
--
Gustavo

>>> @@ -346,13 +346,13 @@ struct hbm_add_client_request {
>>> * @hbm_cmd: bus message command header
>>> * @me_addr: address of the client in ME
>>> * @status: if HBMS_SUCCESS then the client can now accept connections.
>>> - * @reserved: reserved
>>> + * @reserved: reserved for alignment.
>>> */
>>> struct hbm_add_client_response {
>>> u8 hbm_cmd;
>>> u8 me_addr;
>>> u8 status;
>>> - u8 reserved[1];
>>> + u8 reserved;
>>> } __packed;
>>>
>>> /**
>>> @@ -461,7 +461,7 @@ struct hbm_notification {
>>> u8 hbm_cmd;
>>> u8 me_addr;
>>> u8 host_addr;
>>> - u8 reserved[1];
>>> + u8 reserved;
>>> } __packed;
>>>
>>> /**
>>>