[PATCH v4 15/17] module: Introduce hash-based integrity checking

[Eric Biggers]

On Tue, Feb 03, 2026 at 01:19:20PM +0100, Petr Pavlu wrote:
> > +static unsigned int get_pow2(unsigned int val)
> > +{
> > +	return 31 - __builtin_clz(val);
> > +}
> > +
> > +static unsigned int roundup_pow2(unsigned int val)
> > +{
> > +	return 1 << (get_pow2(val - 1) + 1);
> > +}
> > +
> > +static unsigned int log2_roundup(unsigned int val)
> > +{
> > +	return get_pow2(roundup_pow2(val));
> > +}
> 
> In the edge case when the kernel is built with only one module, the code
> calls log2_roundup(1) -> roundup_pow2(1) -> get_pow2(0) ->
> __builtin_clz(0). The return value of __builtin_clz() is undefined if
> the input is zero.

A suggestion:

        static unsigned int log2_roundup(unsigned int val)
        {
                if (val <= 1)
                        return 0;
                return 32 - __builtin_clz(val - 1);
        }

- Eric