On Thu, Oct 04, 2018 at 11:34:29AM -0700, Bart Van Assche wrote: > On Thu, 2018-10-04 at 11:30 -0700, Nathan Chancellor wrote: > > Hi SCSI folks, > > > > In an effort to get the kernel building warning free with Clang, we've > > come across an interesting occurrence in a few scsi drivers: > > > > drivers/scsi/hpsa.c:6533:7: warning: overflow converting case value to switch condition type (2148024833 to 18446744071562609153) [-Wswitch] > > case CCISS_GETPCIINFO: > > ^ > > ./include/uapi/linux/cciss_ioctl.h:65:26: note: expanded from macro 'CCISS_GETPCIINFO' > > #define CCISS_GETPCIINFO _IOR(CCISS_IOC_MAGIC, 1, cciss_pci_info_struct) > > ^ > > ./include/uapi/asm-generic/ioctl.h:86:28: note: expanded from macro '_IOR' > > #define _IOR(type,nr,size) _IOC(_IOC_READ,(type),(nr),(_IOC_TYPECHECK(size))) > > ^ > > ./include/uapi/asm-generic/ioctl.h:70:2: note: expanded from macro '_IOC' > > (((dir) << _IOC_DIRSHIFT) | \ > > ^ > > > > I see this warning in drivers/scsi/hpsa.c and drivers/scsi/smartpqi/smartpqi_init.c > > on an arm64 allyesconfig build and it has also been reported in a couple of files in > > drivers/scsi/cxlflash. > > > > As the warning states, there is an overflow because the switch statement's value is of > > type int but the switch value is greater than INT_MAX. I did a brief sweep of the tree > > and it seems that all uses of _IOC in switch statement values either are small enough > > to fit into size int or the value is of size unsigned int. > > > > I am unsure of the implications of using a smaller _IOC value or converting all ioctls > > to expect a cmd of type unsigned int (especially since that has userspace implications) > > but I didn't see any negative ioctl commands. Some clarity and insight would be > > appreciated. > > Have you verified how gcc compiles these switch statements? Maybe gcc supports > switch / case statements on integral types that are larger than an int? > > Bart. Hi Bart, That is entirely possible, I will do some research. I did build with GCC to see if there was any warning and there isn't so I'll be curious to see what is happening at a lower level. Thanks for the comment! Nathan
