KASSERT(val != 0) not triggering in linux_errno.c reading outside of array

[Hans Petter Selasky]

On 2020-11-03 10:46, xtouqh at hotmail.com wrote:
> I'm looking at the current sys/compat/linux/linux_errno.c source, 
> specifically this function: 
> https://svnweb.freebsd.org/base/head/sys/compat/linux/linux_errno.c?revision=367132&view=markup#l24, 
> and noticed that sizeof() usage there seems to be bogus as I mentioned 
> in https://reviews.freebsd.org/D26974#inline-168811.
> 
> What I'm wondering about is why KASSERT() is not triggering there -- I 
> have added the following printf() right below KASSERT() showing that we 
> indeed read outside of the array, and some of the linux_errtbl[i] values 
> are 0:
> 
> printf("%s:linux_errtbl[%d]=%d\n", __func__, i, linux_errtbl[i]);
> 
> But, if I add the following check before printf(), it seems to be never 
> true:
> 
> if (linux_errtbl[i] == 0)
>      printf("%s:linux_errtbl[%d]=%d\n", __func__, i, linux_errtbl[i]);
> 
> So how come printed values are 0, but KASSERT(value != 0) and if (value 
> == 0) are never true?  I tried to reproduce this in simple userland test 
> case, but the check seems to be working correctly there (though still 
> reading outside of array if using sizeof() for final index).  What am I 
> missing here?

Did you enable INVARIANTS when compiling the kernel?

--HPS