On 08/06/17 17:50, Alexei Starovoitov wrote: > On Thu, Jun 08, 2017 at 04:25:39PM +0100, Edward Cree wrote: >> On 08/06/17 03:35, Alexei Starovoitov wrote: >>> such large back and forth move doesn't help reviewing. >>> may be just merge it into previous patch? >>> Or keep that function in the right place in patch 2 already? >> I think 'diff' got a bit confused, and maybe with different options I could >> have got it to produce something more readable. But I think I will just >> merge this into patch 2; it's only separate because it started out as an >> experiment. > after sleeping on it I'm not sure we should be allowing such pointer > arithmetic. In normal C code people do fancy tricks with lower 3 bits > of the pointer, but in bpf code I cannot see such use case. > What kind of realistic code will be doing ptr & 0x40 ? Well, I didn't support it because I saw a use case. I supported it because it seemed easy to do and the code came out reasonably elegant-looking. Since this is guarded by env->allow_ptr_leaks, I can't see any reason _not_ to let people try fancy tricks with the low bits of pointers. I agree ptr & 0x40 is a crazy thing with no imaginable use case, but... "Unix was not designed to stop its users from doing stupid things, as that would also stop them from doing clever things." ;-)
-Ed
