On 13/03/2018 at 09:29:33 +0100, Stefano Manni wrote: > Hi, > > 2018-03-13 0:31 GMT+01:00 Alexandre Belloni > <alexandre.belloni@xxxxxxxxxxxxxxxxxx>: > > Hi, > > > > On 13/03/2018 at 00:13:38 +0100, Stefano Manni wrote: > >> In preparation to enabling -Wvla, remove VLAs and replace them with > >> fixed-length arrays instead. > >> > >> rtc-mcp795.c uses a variable-length array declaration to contain > >> the command to write the rtcc; this can be replaced by a fixed- > >> size array of length 2 (instruction, address) + 32 (data out), > >> assuming a maximum data length of 32 bytes before wrap up. > >> > >> This was prompted by https://lkml.org/lkml/2018/3/7/621 > >> > >> Signed-off-by: Stefano Manni <stefano.manni@xxxxxxxxx> > >> --- > >> drivers/rtc/rtc-mcp795.c | 8 +++++++- > >> 1 file changed, 7 insertions(+), 1 deletion(-) > >> > >> diff --git a/drivers/rtc/rtc-mcp795.c b/drivers/rtc/rtc-mcp795.c > >> index 77f21331ae21..a5f504e2364c 100644 > >> --- a/drivers/rtc/rtc-mcp795.c > >> +++ b/drivers/rtc/rtc-mcp795.c > >> @@ -61,6 +61,9 @@ > >> > >> #define SEC_PER_DAY (24 * 60 * 60) > >> > >> +/* Maximum length for data out in write operation to RTCC */ > >> +#define MCP795_MAX_DATAOUT_LEN 32 > >> + > > > > This is wrong, see https://marc.info/?l=linux-kernel&m=152046370320811&w=2 > > > > Also, https://git.kernel.org/pub/scm/linux/kernel/git/abelloni/linux.git/commit/?h=rtc-next&id=74ce1a932504da166cfbccf5567aa3751b6aa599 > > > > You sure that the right value to use is 255 + 2? mcp795_rtcc_write() just writes > into the RTCC that contains only 32 registers (table 4-1 of > datasheet). I assumed > 32 as the maximum length of data to write before wrapping up (start > from reg 0x0). > Probably 32 is just a wrong assumption but why did you choose 255? > It is not so wrong but the plan is to be able to support reading/writing the EEPROM later but I agree it will need to be changed anyway. > Another thing: don't we need also to check count against the array length? > > if (count > MCP795_MAX_DATAOUT_LEN) > return -EINVAL; u8 count will never be greater than 255. -- Alexandre Belloni, Bootlin (formerly Free Electrons) Embedded Linux and Kernel engineering https://bootlin.com
