Re: [PATCH 2/2] test_firmware: silence underflow warning in test_dev_config_update_u8()
From: Andrew Morton
Date: Thu Feb 21 2019 - 14:54:32 EST
On Thu, 21 Feb 2019 22:18:56 +0300 Dan Carpenter <dan.carpenter@xxxxxxxxxx> 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@xxxxxxxxxx> 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.
> It would be more clear to just write it as:
> #define U8_MAX 0xff
That doesn't work either. Tricky.
typedef unsigned char u8;
#define U8_MAX 0xff
int main(int argc, char *argv)
new = -20;
if (new > U8_MAX)