On Thu, May 21, 2015 at 9:40 AM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote: > On 5/21/15 9:20 AM, Andy Lutomirski wrote: >> >> >> What I mean is: why do we need the interface to be "look up this index >> in an array and just to what it references" as a single atomic >> instruction? Can't we break it down into first "look up this index in >> an array" and then "do this tail call"? > > > I've actually considered to do this split and do first part as map lookup > and 2nd as 'tail call to this ptr' insn, but it turned out to be > painful: verifier gets more complicated, ctx pointer needs to kept > somewhere, JITs need to special case two things instead of one. > Also I couldn't see a use case for exposing program pointer to the > program itself. I've explored this path only because it felt more > traditional 'goto *ptr' like, but adding new PTR_TO_PROG type to > verifier looked wasteful. At some point, I think that it would be worth extending the verifier to support more general non-integral scalar types. "Pointer to tail-call target" would be just one of them. "Pointer to skb" might be nice as a real first-class scalar type that lives in a register as opposed to just being magic typed context. We'd still need some way to stick fds into a map, but that's not really the verifier's problem. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
