Messages in this thread | | | Subject | Re: [PATCH] rtc: remove VLA usage | From | "Gustavo A. R. Silva" <> | Date | Wed, 7 Mar 2018 17:09:22 -0600 |
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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 <gustavo@embeddedor.com> >>>> --- >>>> 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
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