Messages in this thread | | | Date | Thu, 21 Feb 2019 11:54:26 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 2/2] test_firmware: silence underflow warning in test_dev_config_update_u8() |
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On Thu, 21 Feb 2019 22:18:56 +0300 Dan Carpenter <dan.carpenter@oracle.com> wrote:
> On Thu, Feb 21, 2019 at 10:54:58AM -0800, Andrew Morton wrote: > > On Thu, 21 Feb 2019 21:38:26 +0300 Dan Carpenter <dan.carpenter@oracle.com> wrote: > > > > > We put an upper bound on "new" but we don't check for negatives. > > > > U8_MAX has unsigned type, so `if (new > U8_MAX)' does check for negative. > > > > No, doesn't work in this case. > > #define U8_MAX ((u8)~0U) > > It would need to unsigned long for the type promotion to prevent > negatives, but it starts as unsigned int, then unsigned char, which is > type promoted to int.
OK.
> It would be more clear to just write it as: > > #define U8_MAX 0xff
That doesn't work either. Tricky.
#include <stdio.h>
typedef unsigned char u8;
#define U8_MAX 0xff
int main(int argc, char *argv[]) { long new;
new = -20;
if (new > U8_MAX) printf("over\n"); }
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