On Mon, Apr 08, 2024 at 10:01:12AM +0200, Clément Léger wrote: > > > On 05/04/2024 19:33, Deepak Gupta wrote: > > On Fri, Apr 5, 2024 at 8:26 AM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote: > >> > >> On Thu, Apr 04, 2024 at 12:32:46PM +0200, Clément Léger wrote: > >>> The Zimop ISA extension was ratified recently. This series adds support > >>> for parsing it from riscv,isa, hwprobe export and kvm support for > >>> Guest/VM. > >> > >> I'm not sure we need this. Zimop by itself isn't useful, so I don't know > >> if we need to advertise it at all. When an extension comes along that > >> redefines some MOPs, then we'll advertise that extension, but the fact > >> Zimop is used for that extension is really just an implementation detail. > > > > Only situation I see this can be useful is this:-- > > > > An implementer, implemented Zimops in CPU solely for the purpose that they can > > run mainline distro & packages on their hardware and don't want to leverage any > > feature which are built on top of Zimop. > > Yes, the rationale was that some binaries using extensions that overload > MOPs could still be run. With Zimop exposed, the loader could determine > if the binary can be executed without potentially crashing. We could > also let the program run anyway but the execution could potentially > crash unexpectedly, which IMHO is not really good for the user > experience nor for debugging. I already think that the segfaults which > happens when executing binaries that need some missing extension are not > so easy to debug, so better add more guards. OK. It's only one more extension out of dozens, so I won't complain more, but I was thinking that binaries that use particular extensions would check for those particular extensions (step 2), rather than Zimop. Thanks, drew > > > > > As an example zicfilp and zicfiss are dependent on zimops. glibc can > > do following > > > > 1) check elf header if binary was compiled with zicfiss and zicfilp, > > if yes goto step 2, else goto step 6. > > 2) check if zicfiss/zicfilp is available in hw via hwprobe, if yes > > goto step 5. else goto step 3 > > 3) check if zimop is available via hwprobe, if yes goto step 6, else goto step 4 > > I think you meant step 5 rather than step 6. > > Clément > > > 4) This binary won't be able to run successfully on this platform, > > issue exit syscall. <-- termination > > 5) issue prctl to enable shadow stack and landing pad for current task > > <-- enable feature > > 6) let the binary run <-- let the binary run because no harm can be done
