Il 09/10/2012 18:19, Aurelien Jarno ha scritto: >>> > > >> > >> > Instead of calling the MMU helper with an additional argument (7), and >> > then jump back (8) to the next code (4), what about pushing the address >> > of the next code (4) on the stack and use a jmp instead of the call. In >> > that case you don't need the extra argument to the helpers. >> > > Maybe it wasn't very clear. This is based on the fact that call is > basically push %rip + jmp. Therefore we can fake the return address by > putting the value we want, here the address of the next code. This mean > that we don't need to pass the extra argument to the helper for the > return address, as GET_PC() would work correctly (it basically reads the > return address on the stack). > > For other architectures, it might not be a push, but rather a move to > link register, basically put the return address where the calling > convention asks for. > > OTOH I just realized it only works if the end of the slow path (moving > the value from the return address to the correct register). It might be > something doable.
Branch predictors will not oldschool tricks like this one. :) Paolo
