[PATCH v2] random: vDSO: Avoid call to memset() when zeroing reserved in __cvdso_getrandom_data()

[David Laight]

On Sat, 26 Sep 2026 14:32:49 +0200
"Jason A. Donenfeld" <Jason at zx2c4.com> wrote:

> On Sat, Sep 26, 2026 at 01:19:27PM +0100, Nathan Chancellor wrote:
> > On Sat, Sep 26, 2026 at 11:39:43AM +0200, Andreas Schwab wrote:  
> > > On Sep 25 2026, Nathan Chancellor wrote:
> > >   
> > > > +#if __has_builtin(__builtin_memset_inline)
> > > > +#define memset_inline(dst, value, size) __builtin_memset_inline(dst, value, size)
> > > > +#elif IS_ENABLED(CONFIG_CC_HAS_OPT_INLINE_MEMSET)
> > > > +#define memset_inline(dst, value, size) __builtin_memset(dst, value, size)
> > > > +#else
> > > > +static inline void *memset_inline(void *dst, int value, size_t size)
> > > > +{
> > > > +	char *d = dst;
> > > > +
> > > > +	while (size--)
> > > > +		*d++ = value;
> > > > +
> > > > +	return d;
> > > > +}
> > > > +#endif
> > > > +  
> > > 
> > > memset actually returns the original pointer, not the incremented one.
> > > Nothing uses the return value of memset_inline here, but it is
> > > confusing.  
> > 
> > Whoops, good catch, I guess my fingers gave up on those last two
> > characters :) I will fix this for v3 once there has been some time for
> > further review.  
> 
> Do we even need to return a value at all? Might as well just make the
> function two lines:
> 
> +       for (char *d = dst; size--;)
> +               *d++ = value;

Wouldn't it be better to add a barrier() or similar in there to
stop the compiler playing unwanted games>

David

> 
> (Technically that could even be one, but maybe that sort of golf loses
> clarity. Your choice.)
>