Re: [PATCH v4 19/39] unwind_user/sframe: Add support for reading .sframe contents

On Thu, Jan 30, 2025 at 04:47:00PM +0100, Jens Remus wrote:
> On 22.01.2025 03:31, Josh Poimboeuf wrote:
> > +struct sframe_fre {
> > +	unsigned int	size;
> > +	s32		ip_off;
> 
> The IP offset (from function start) in the SFrame V2 FDE is unsigned:
> 
> u32 ip_off;

Indeed.

> > +#define __UNSAFE_GET_USER_INC(to, from, type, label)			\
> > +({									\
> > +	type __to;							\
> > +	unsafe_get_user(__to, (type __user *)from, label);		\
> > +	from += sizeof(__to);						\
> > +	to = (typeof(to))__to;							\
> > +})
> > +
> > +#define UNSAFE_GET_USER_INC(to, from, size, label)			\
> > +({									\
> > +	switch (size) {							\
> > +	case 1:								\
> > +		__UNSAFE_GET_USER_INC(to, from, u8, label);		\
> > +		break;							\
> > +	case 2:								\
> > +		__UNSAFE_GET_USER_INC(to, from, u16, label);		\
> > +		break;							\
> > +	case 4:								\
> > +		__UNSAFE_GET_USER_INC(to, from, u32, label);		\
> > +		break;							\
> > +	default:							\
> > +		return -EFAULT;						\
> > +	}								\
> > +})
> 
> This does not work for the signed SFrame fields, such as the FRE CFA,
> RA, and FP offsets, as it does not perform the required sign extension.
> One option would be to rename to UNSAFE_GET_USER_UNSIGNED_INC() and
> re-introduce UNSAFE_GET_USER_SIGNED_INC() using s8, s16, and s32.

See the following line in __UNSAFE_GET_USER_INC():

	to = (typeof(to))__to;

Does that not do the sign extension?

-- 
Josh