LinuxLists.cc - [PATCH] rtc: remove VLA usage

2018-03-07 20:35:06

Subject: [PATCH] rtc: remove VLA usage

In preparation to enabling -Wvla, remove VLA and replace it
with a fixed-length array instead.

Signed-off-by: Gustavo A. R. Silva <[email protected]>
---
drivers/rtc/rtc-bq32k.c | 2 +-
drivers/rtc/rtc-mcp795.c | 2 +-
2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
index e8698e9..e4b234a 100644
--- a/drivers/rtc/rtc-bq32k.c
+++ b/drivers/rtc/rtc-bq32k.c
@@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
{
struct i2c_client *client = to_i2c_client(dev);
- uint8_t buffer[len + 1];
+ uint8_t buffer[256];

buffer[0] = off;
memcpy(&buffer[1], data, len);
diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
index 79e24ea..00e11c1 100644
--- a/drivers/rtc/rtc-mcp795.c
+++ b/drivers/rtc/rtc-mcp795.c
@@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
{
struct spi_device *spi = to_spi_device(dev);
int ret;
- u8 tx[2 + count];
+ u8 tx[257];

tx[0] = MCP795_WRITE;
tx[1] = addr;
--
2.7.4

2018-03-07 21:26:47

by Alexandre Belloni

[permalink] [raw]

Subject: Re: [PATCH] rtc: remove VLA usage

On 07/03/2018 at 14:11:33 -0600, Gustavo A. R. Silva wrote:
> In preparation to enabling -Wvla, remove VLA and replace it
> with a fixed-length array instead.
>

You should probably explain what VLA is and why this is important to do.

> Signed-off-by: Gustavo A. R. Silva <[email protected]>
> ---
> drivers/rtc/rtc-bq32k.c | 2 +-
> drivers/rtc/rtc-mcp795.c | 2 +-
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
> index e8698e9..e4b234a 100644
> --- a/drivers/rtc/rtc-bq32k.c
> +++ b/drivers/rtc/rtc-bq32k.c
> @@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
> static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
> {
> struct i2c_client *client = to_i2c_client(dev);
> - uint8_t buffer[len + 1];
> + uint8_t buffer[256];
>

You chose to change len to 255, probably because this is a uint8_t but
this is way too much for this rtc, it only has 10 consecutive registers.

> buffer[0] = off;
> memcpy(&buffer[1], data, len);
> diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
> index 79e24ea..00e11c1 100644
> --- a/drivers/rtc/rtc-mcp795.c
> +++ b/drivers/rtc/rtc-mcp795.c
> @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
> {
> struct spi_device *spi = to_spi_device(dev);
> int ret;
> - u8 tx[2 + count];
> + u8 tx[257];
>
> tx[0] = MCP795_WRITE;
> tx[1] = addr;
> --
> 2.7.4
>

--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

2018-03-07 22:41:05

by Gustavo A. R. Silva

[permalink] [raw]

Subject: Re: [PATCH] rtc: remove VLA usage

Hi Alexandre,

On 03/07/2018 03:25 PM, Alexandre Belloni wrote:
> On 07/03/2018 at 14:11:33 -0600, Gustavo A. R. Silva wrote:
>> In preparation to enabling -Wvla, remove VLA and replace it
>> with a fixed-length array instead.
>>
> You should probably explain what VLA is and why this is important to do.

Sure. I can elaborate a little bit more.

>> Signed-off-by: Gustavo A. R. Silva <[email protected]>
>> ---
>> drivers/rtc/rtc-bq32k.c | 2 +-
>> drivers/rtc/rtc-mcp795.c | 2 +-
>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
>> index e8698e9..e4b234a 100644
>> --- a/drivers/rtc/rtc-bq32k.c
>> +++ b/drivers/rtc/rtc-bq32k.c
>> @@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
>> static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
>> {
>> struct i2c_client *client = to_i2c_client(dev);
>> - uint8_t buffer[len + 1];
>> + uint8_t buffer[256];
>>
> You chose to change len to 255, probably because this is a uint8_t but

Correct.

> this is way too much for this rtc, it only has 10 consecutive registers.

In that case probably the best solution is to add the following line to
the module:

#define MAX_LEN 10

and update the rest of the code as follows:

uint8_t buffer[MAX_LEN + 1];

>> buffer[0] = off;
>> memcpy(&buffer[1], data, len);
>> diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
>> index 79e24ea..00e11c1 100644
>> --- a/drivers/rtc/rtc-mcp795.c
>> +++ b/drivers/rtc/rtc-mcp795.c
>> @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
>> {
>> struct spi_device *spi = to_spi_device(dev);
>> int ret;
>> - u8 tx[2 + count];
>> + u8 tx[257];

For this particular case it seems to me that the following works just fine:

#define MAX_COUNT 7

u8 tx[MAX_COUNT + 2];

What do you think?

Thanks for your feedback.
--
Gustavo

>>
>> tx[0] = MCP795_WRITE;
>> tx[1] = addr;
>> --
>> 2.7.4
>>

2018-03-07 22:41:44

by Gustavo A. R. Silva

[permalink] [raw]

Subject: Re: [PATCH] rtc: remove VLA usage

2018-03-07 23:02:48

by Alexandre Belloni

[permalink] [raw]

Subject: Re: [PATCH] rtc: remove VLA usage

On 07/03/2018 at 16:39:51 -0600, Gustavo A. R. Silva wrote:
> Hi Alexandre,
>
> On 03/07/2018 03:25 PM, Alexandre Belloni wrote:
> > On 07/03/2018 at 14:11:33 -0600, Gustavo A. R. Silva wrote:
> > > In preparation to enabling -Wvla, remove VLA and replace it
> > > with a fixed-length array instead.
> > >
> > You should probably explain what VLA is and why this is important to do.
>
> Sure. I can elaborate a little bit more.
>
> > > Signed-off-by: Gustavo A. R. Silva <[email protected]>
> > > ---
> > > drivers/rtc/rtc-bq32k.c | 2 +-
> > > drivers/rtc/rtc-mcp795.c | 2 +-
> > > 2 files changed, 2 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
> > > index e8698e9..e4b234a 100644
> > > --- a/drivers/rtc/rtc-bq32k.c
> > > +++ b/drivers/rtc/rtc-bq32k.c
> > > @@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
> > > static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
> > > {
> > > struct i2c_client *client = to_i2c_client(dev);
> > > - uint8_t buffer[len + 1];
> > > + uint8_t buffer[256];
> > You chose to change len to 255, probably because this is a uint8_t but
>
> Correct.
>
> > this is way too much for this rtc, it only has 10 consecutive registers.
>
> In that case probably the best solution is to add the following line to the
> module:
>
> #define MAX_LEN 10
>
> and update the rest of the code as follows:
>
> uint8_t buffer[MAX_LEN + 1];
>

Seems better, yes.

>
> > > buffer[0] = off;
> > > memcpy(&buffer[1], data, len);
> > > diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
> > > index 79e24ea..00e11c1 100644
> > > --- a/drivers/rtc/rtc-mcp795.c
> > > +++ b/drivers/rtc/rtc-mcp795.c
> > > @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
> > > {
> > > struct spi_device *spi = to_spi_device(dev);
> > > int ret;
> > > - u8 tx[2 + count];
> > > + u8 tx[257];
>
> For this particular case it seems to me that the following works just fine:
>
> #define MAX_COUNT 7
>
> u8 tx[MAX_COUNT + 2];
>
> What do you think?
>

Nope, that RTC has a section of 255 bytes that could be read at once so
257 is the correct value.

--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

2018-03-07 23:12:55

by Gustavo A. R. Silva

[permalink] [raw]

Subject: Re: [PATCH] rtc: remove VLA usage

On 03/07/2018 05:01 PM, Alexandre Belloni wrote:
> On 07/03/2018 at 16:39:51 -0600, Gustavo A. R. Silva wrote:
>> Hi Alexandre,
>>
>> On 03/07/2018 03:25 PM, Alexandre Belloni wrote:
>>> On 07/03/2018 at 14:11:33 -0600, Gustavo A. R. Silva wrote:
>>>> In preparation to enabling -Wvla, remove VLA and replace it
>>>> with a fixed-length array instead.
>>>>
>>> You should probably explain what VLA is and why this is important to do.
>> Sure. I can elaborate a little bit more.
>>
>>>> Signed-off-by: Gustavo A. R. Silva <[email protected]>
>>>> ---
>>>> drivers/rtc/rtc-bq32k.c | 2 +-
>>>> drivers/rtc/rtc-mcp795.c | 2 +-
>>>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>>>
>>>> diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
>>>> index e8698e9..e4b234a 100644
>>>> --- a/drivers/rtc/rtc-bq32k.c
>>>> +++ b/drivers/rtc/rtc-bq32k.c
>>>> @@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
>>>> static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
>>>> {
>>>> struct i2c_client *client = to_i2c_client(dev);
>>>> - uint8_t buffer[len + 1];
>>>> + uint8_t buffer[256];
>>> You chose to change len to 255, probably because this is a uint8_t but
>> Correct.
>>
>>> this is way too much for this rtc, it only has 10 consecutive registers.
>> In that case probably the best solution is to add the following line to the
>> module:
>>
>> #define MAX_LEN 10
>>
>> and update the rest of the code as follows:
>>
>> uint8_t buffer[MAX_LEN + 1];
>>
> Seems better, yes.
>
>>>> buffer[0] = off;
>>>> memcpy(&buffer[1], data, len);
>>>> diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
>>>> index 79e24ea..00e11c1 100644
>>>> --- a/drivers/rtc/rtc-mcp795.c
>>>> +++ b/drivers/rtc/rtc-mcp795.c
>>>> @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
>>>> {
>>>> struct spi_device *spi = to_spi_device(dev);
>>>> int ret;
>>>> - u8 tx[2 + count];
>>>> + u8 tx[257];
>> For this particular case it seems to me that the following works just fine:
>>
>> #define MAX_COUNT 7
>>
>> u8 tx[MAX_COUNT + 2];
>>
>> What do you think?
>>
> Nope, that RTC has a section of 255 bytes that could be read at once so
> 257 is the correct value.
>

I see...

I was looking into this piece of code drivers/rtc/rtc-mcp795.c:302:

        tmp[0] = (tmp[0] & 0x80) | bin2bcd(alm->time.tm_sec);
        tmp[1] = (tmp[1] & 0x80) | bin2bcd(alm->time.tm_min);
        tmp[2] = (tmp[2] & 0xE0) | bin2bcd(alm->time.tm_hour);
        tmp[3] = (tmp[3] & 0x80) | bin2bcd(alm->time.tm_wday + 1);
        /* set alarm match: seconds, minutes, hour, day, date and month */
        tmp[3] |= (MCP795_ALM0C2_BIT | MCP795_ALM0C1_BIT |
MCP795_ALM0C0_BIT);
        tmp[4] = (tmp[4] & 0xC0) | bin2bcd(alm->time.tm_mday);
        tmp[5] = (tmp[5] & 0xE0) | bin2bcd(alm->time.tm_mon + 1);

        ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp,
sizeof(tmp));

OK. I'll work on v2 of this patch. I'll send it shortly.

Thanks
--
Gustavo

2018-03-07 23:14:11

by Alexandre Belloni

[permalink] [raw]

Subject: Re: [PATCH] rtc: remove VLA usage

On 07/03/2018 at 17:09:22 -0600, Gustavo A. R. Silva wrote:
>
>
> On 03/07/2018 05:01 PM, Alexandre Belloni wrote:
> > On 07/03/2018 at 16:39:51 -0600, Gustavo A. R. Silva wrote:
> > > Hi Alexandre,
> > >
> > > On 03/07/2018 03:25 PM, Alexandre Belloni wrote:
> > > > On 07/03/2018 at 14:11:33 -0600, Gustavo A. R. Silva wrote:
> > > > > In preparation to enabling -Wvla, remove VLA and replace it
> > > > > with a fixed-length array instead.
> > > > >
> > > > You should probably explain what VLA is and why this is important to do.
> > > Sure. I can elaborate a little bit more.
> > >
> > > > > Signed-off-by: Gustavo A. R. Silva <[email protected]>
> > > > > ---
> > > > > drivers/rtc/rtc-bq32k.c | 2 +-
> > > > > drivers/rtc/rtc-mcp795.c | 2 +-
> > > > > 2 files changed, 2 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
> > > > > index e8698e9..e4b234a 100644
> > > > > --- a/drivers/rtc/rtc-bq32k.c
> > > > > +++ b/drivers/rtc/rtc-bq32k.c
> > > > > @@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
> > > > > static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
> > > > > {
> > > > > struct i2c_client *client = to_i2c_client(dev);
> > > > > - uint8_t buffer[len + 1];
> > > > > + uint8_t buffer[256];
> > > > You chose to change len to 255, probably because this is a uint8_t but
> > > Correct.
> > >
> > > > this is way too much for this rtc, it only has 10 consecutive registers.
> > > In that case probably the best solution is to add the following line to the
> > > module:
> > >
> > > #define MAX_LEN 10
> > >
> > > and update the rest of the code as follows:
> > >
> > > uint8_t buffer[MAX_LEN + 1];
> > >
> > Seems better, yes.
> >
> > > > > buffer[0] = off;
> > > > > memcpy(&buffer[1], data, len);
> > > > > diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
> > > > > index 79e24ea..00e11c1 100644
> > > > > --- a/drivers/rtc/rtc-mcp795.c
> > > > > +++ b/drivers/rtc/rtc-mcp795.c
> > > > > @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
> > > > > {
> > > > > struct spi_device *spi = to_spi_device(dev);
> > > > > int ret;
> > > > > - u8 tx[2 + count];
> > > > > + u8 tx[257];
> > > For this particular case it seems to me that the following works just fine:
> > >
> > > #define MAX_COUNT 7
> > >
> > > u8 tx[MAX_COUNT + 2];
> > >
> > > What do you think?
> > >
> > Nope, that RTC has a section of 255 bytes that could be read at once so
> > 257 is the correct value.
> >
>
> I see...
>
> I was looking into this piece of code drivers/rtc/rtc-mcp795.c:302:
>
> ??????? tmp[0] = (tmp[0] & 0x80) | bin2bcd(alm->time.tm_sec);
> ??????? tmp[1] = (tmp[1] & 0x80) | bin2bcd(alm->time.tm_min);
> ??????? tmp[2] = (tmp[2] & 0xE0) | bin2bcd(alm->time.tm_hour);
> ??????? tmp[3] = (tmp[3] & 0x80) | bin2bcd(alm->time.tm_wday + 1);
> ??????? /* set alarm match: seconds, minutes, hour, day, date and month */
> ??????? tmp[3] |= (MCP795_ALM0C2_BIT | MCP795_ALM0C1_BIT |
> MCP795_ALM0C0_BIT);
> ??????? tmp[4] = (tmp[4] & 0xC0) | bin2bcd(alm->time.tm_mday);
> ??????? tmp[5] = (tmp[5] & 0xE0) | bin2bcd(alm->time.tm_mon + 1);
>
> ??????? ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp,
> sizeof(tmp));
>

Yeah, the 128 or 255 bytes NVRAM is not yet supported but this is on my
todo list

--
Alexandre Belloni, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

2018-03-07 23:40:11

by Gustavo A. R. Silva

[permalink] [raw]

Subject: Re: [PATCH] rtc: remove VLA usage

On 03/07/2018 05:12 PM, Alexandre Belloni wrote:
> On 07/03/2018 at 17:09:22 -0600, Gustavo A. R. Silva wrote:
>>
>> On 03/07/2018 05:01 PM, Alexandre Belloni wrote:
>>> On 07/03/2018 at 16:39:51 -0600, Gustavo A. R. Silva wrote:
>>>> Hi Alexandre,
>>>>
>>>> On 03/07/2018 03:25 PM, Alexandre Belloni wrote:
>>>>> On 07/03/2018 at 14:11:33 -0600, Gustavo A. R. Silva wrote:
>>>>>> In preparation to enabling -Wvla, remove VLA and replace it
>>>>>> with a fixed-length array instead.
>>>>>>
>>>>> You should probably explain what VLA is and why this is important to do.
>>>> Sure. I can elaborate a little bit more.
>>>>
>>>>>> Signed-off-by: Gustavo A. R. Silva <[email protected]>
>>>>>> ---
>>>>>> drivers/rtc/rtc-bq32k.c | 2 +-
>>>>>> drivers/rtc/rtc-mcp795.c | 2 +-
>>>>>> 2 files changed, 2 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/rtc/rtc-bq32k.c b/drivers/rtc/rtc-bq32k.c
>>>>>> index e8698e9..e4b234a 100644
>>>>>> --- a/drivers/rtc/rtc-bq32k.c
>>>>>> +++ b/drivers/rtc/rtc-bq32k.c
>>>>>> @@ -74,7 +74,7 @@ static int bq32k_read(struct device *dev, void *data, uint8_t off, uint8_t len)
>>>>>> static int bq32k_write(struct device *dev, void *data, uint8_t off, uint8_t len)
>>>>>> {
>>>>>> struct i2c_client *client = to_i2c_client(dev);
>>>>>> - uint8_t buffer[len + 1];
>>>>>> + uint8_t buffer[256];
>>>>> You chose to change len to 255, probably because this is a uint8_t but
>>>> Correct.
>>>>
>>>>> this is way too much for this rtc, it only has 10 consecutive registers.
>>>> In that case probably the best solution is to add the following line to the
>>>> module:
>>>>
>>>> #define MAX_LEN 10
>>>>
>>>> and update the rest of the code as follows:
>>>>
>>>> uint8_t buffer[MAX_LEN + 1];
>>>>
>>> Seems better, yes.
>>>
>>>>>> buffer[0] = off;
>>>>>> memcpy(&buffer[1], data, len);
>>>>>> diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c
>>>>>> index 79e24ea..00e11c1 100644
>>>>>> --- a/drivers/rtc/rtc-mcp795.c
>>>>>> +++ b/drivers/rtc/rtc-mcp795.c
>>>>>> @@ -82,7 +82,7 @@ static int mcp795_rtcc_write(struct device *dev, u8 addr, u8 *data, u8 count)
>>>>>> {
>>>>>> struct spi_device *spi = to_spi_device(dev);
>>>>>> int ret;
>>>>>> - u8 tx[2 + count];
>>>>>> + u8 tx[257];
>>>> For this particular case it seems to me that the following works just fine:
>>>>
>>>> #define MAX_COUNT 7
>>>>
>>>> u8 tx[MAX_COUNT + 2];
>>>>
>>>> What do you think?
>>>>
>>> Nope, that RTC has a section of 255 bytes that could be read at once so
>>> 257 is the correct value.
>>>
>> I see...
>>
>> I was looking into this piece of code drivers/rtc/rtc-mcp795.c:302:
>>
>>         tmp[0] = (tmp[0] & 0x80) | bin2bcd(alm->time.tm_sec);
>>         tmp[1] = (tmp[1] & 0x80) | bin2bcd(alm->time.tm_min);
>>         tmp[2] = (tmp[2] & 0xE0) | bin2bcd(alm->time.tm_hour);
>>         tmp[3] = (tmp[3] & 0x80) | bin2bcd(alm->time.tm_wday + 1);
>>         /* set alarm match: seconds, minutes, hour, day, date and month */
>>         tmp[3] |= (MCP795_ALM0C2_BIT | MCP795_ALM0C1_BIT |
>> MCP795_ALM0C0_BIT);
>>         tmp[4] = (tmp[4] & 0xC0) | bin2bcd(alm->time.tm_mday);
>>         tmp[5] = (tmp[5] & 0xE0) | bin2bcd(alm->time.tm_mon + 1);
>>
>>         ret = mcp795_rtcc_write(dev, MCP795_REG_ALM0_SECONDS, tmp,
>> sizeof(tmp));
>>
> Yeah, the 128 or 255 bytes NVRAM is not yet supported but this is on my
> todo list
>

I got it.

Thanks
--
Gustavo