Re: [PATCH] Staging/comedi: Fixes static analysis warning raised by sparse

[josh@joshtriplett.org]

On Thu, Jun 12, 2014 at 12:24:25AM +0300, Dan Carpenter wrote:
> Let's forward this to the Sparse mailing list.
> 
> We're seeing a Sparse false positive testing
> drivers/staging/comedi/drivers/ni_pcimio.c.
> 
>   CHECK   drivers/staging/comedi/drivers/ni_pcimio.c
> drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> drivers/staging/comedi/drivers/ni_stc.h:720:26: warning: shift too big (4294967295) for type int
> 
> I have created some test code to demonstrate the problem (attached).
> 
> The check_shift_count() warning is only supposed to be printed for
> number literals but because of the way inline functions are expanded it
> still complains even though channel is a variable.

Thanks for the test case; this definitely makes no sense.  I don't think
Sparse will suddenly develop enough range analysis or reachability
analysis to handle this case; I think the right answer is to avoid
giving such warnings for shifts with a non-constant RHS.

> #include <stdio.h>
> #include <limits.h>
> #include <string.h>
> 
> static inline unsigned ni_stc_dma_channel_select_bitfield(unsigned channel)
> {
> 	if (channel < 4)
> 		return 1 << channel;
> 	return 0;
> }
> 
> static inline void filter(int channel)
> {
> 	if (channel < 0)
> 		return;
> 	ni_stc_dma_channel_select_bitfield(channel);
> }
> 
> int main(void)
> {
> 	filter(-1);
> 
> 	return 0;
> }