Aaron Lindsay <aa...@os.amperecomputing.com> writes:
> Hi folks, > > I see there has been some previous discussion [1] about 1.5 years ago > around the fact that AArch64 SVE instructions do not emit any memory > operations via the plugin interface, as one might expect them to. > > I am interested in being able to more accurately trace the memory > operations of SVE instructions using the plugin interface - has there > been any further discussion or work on this topic off-list (or that > escaped my searching)? > > In the previous discussion [1], Richard raised some interesting > questions: > >> The plugin interface needs extension for this. How should I signal that 256 >> consecutive byte loads have occurred? How should I signal that the >> controlling >> predicate was not all true, so only 250 of those 256 were actually active? >> How >> should I signal 59 non-consecutive (gather) loads have occurred? >> >> If the answer is simply that you want 256 or 250 or 59 plugin callbacks >> respectively, then we might be able to force the memory operations into the >> slow path, and hook the operation there. As if it were an i/o operation. > > My initial reaction is that simply sending individual callbacks for each > access (only the ones which were active, in the case of predication) > seems to fit reasonably well with the existing plugin interface. For > instance, I think we already receive two callbacks for each AArch64 > `LDP` instruction, right? This seems the simplest solution. I think what you need to look at is how the sve_ldst1_host_fn and sve_ldst1_tlb_fn functions eventually emerge out of the macro expansion (having a -E copy of the compiled source might be helpful here). That said I'm confused that softmmu isn't already hooked into by virtue of using the softmmu slowpath (cpu_[ld|st]_*). However user space emulation which typically directly accesses a final host address will need to be fixed. > If this is an agreeable solution that wouldn't take too much effort to > implement (and no one else is doing it), would someone mind pointing me > in the right direction to get started? Richard, anything to add? > > Thanks! > > -Aaron > > [1] https://lists.nongnu.org/archive/html/qemu-discuss/2020-12/msg00015.html -- Alex Bennée