Re: linux-next: build failure after merge of the kspp tree

[Masami Hiramatsu]

On Tue, 25 Jan 2022 22:27:32 +0900
Masami Hiramatsu <mhiramat@xxxxxxxxxx> wrote:

> > /*
> >  * struct trace_event_data_offsets_<call> {
> >  *      u32                             <item1>;
> >  *      u32                             <item2>;
> >  *      [...]
> >  * };
> >  *
> >  * The __dynamic_array() macro will create each u32 <item>, this is
> >  * to keep the offset of each array from the beginning of the event.
> >  * The size of an array is also encoded, in the higher 16 bits of
> >  * <item>.
> >  */
> > 
> > So, I think -Warray-bounds is refusing to see the destination as
> > anything except a u32, but being accessed at 4 (sizeof(u32)) + 8
> > (address && 0xffff) (?)
> 
> Ah, I got it. Yes, that's right. __data_loc() will access the data
> from the __entry, but the __rel_loc() points the same address from
> the encoded field ("__rel_loc_foo" in this case) itself.
> This is introduced for the user application event, which doesn't
> know the actual __entry size because the __entry includes some
> kernel internal defined fields.
> 
> > But if this is true, I would imagine there would be plenty of other
> > warnings? I'm currently stumped.
> 
> That is because __rel_loc is used only in the sample code in the kernel
> for testing. Other use-cases comes from user-space.
> Hmm, can we skip this boundary check for this example?

If the -Warray-bounds determines the destination array size from
the type of given pointer, we can just change the macro as below;

#define __get_rel_dynamic_array(field) 
			((void *)__entry +                                 \
			 offsetof(typeof(*__entry), __rel_loc_##field) +   \
			 sizeof(__entry->__rel_loc_##field) +              \
			 (__entry->__rel_loc_##field & 0xffff))

This must works same as __get_dynamic_array() macro.

Could you try this patch?