> On Jan 10, 2019, at 12:57 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > > On Thu, Jan 10, 2019 at 08:48:31PM +0000, Nadav Amit wrote: >>> On Jan 10, 2019, at 12:32 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: >>> >>> On Thu, Jan 10, 2019 at 07:45:26PM +0000, Nadav Amit wrote: >>>>>> I’m not GCC expert either and writing this code was not making me full of >>>>>> joy, etc.. I’ll be happy that my code would be reviewed, but it does >>>>>> work. I >>>>>> don’t think an early pass is needed, as long as hardware registers were >>>>>> not >>>>>> allocated. >>>>>> >>>>>>> Would it work with more than 5 arguments, where args get passed on the >>>>>>> stack? >>>>>> >>>>>> It does. >>>>>> >>>>>>> At the very least, it would (at least partially) defeat the point of the >>>>>>> callee-saved paravirt ops. >>>>>> >>>>>> Actually, I think you can even deal with callee-saved functions and >>>>>> remove >>>>>> all the (terrible) macros. You would need to tell the extension not to >>>>>> clobber the registers through a new attribute. >>>>> >>>>> Ok, it does sound interesting then. I assume you'll be sharing the >>>>> code? >>>> >>>> Of course. If this what is going to convince, I’ll make a small version for >>>> PV callee-saved first. >>> >>> It wasn't *only* the PV callee-saved part which interested me, so if you >>> already have something which implements the other parts, I'd still like >>> to see it. >> >> Did you have a look at >> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flkml%2F20181231072112.21051-4-namit%40vmware.com%2F&data=02%7C01%7Cnamit%40vmware.com%7C169b737792134fc852d808d6773e454b%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C636827506683819442&sdata=FhM%2F5OD%2FNHx9Jr97iPIBNyn0BoLAlyiSv%2BT4XICBUdg%3D&reserved=0 >> ? >> >> See the changes to x86_call_markup_plugin.c . >> >> The missing part (that I just finished but need to cleanup) is attributes >> that allow you to provide key and dynamically enable the patching. > > Aha, so it's the basically the same plugin you had for optpolines. I > missed that. I'll need to stare at the code for a little bit.
Pretty much. You would want to change the assembly code block, and based on the use-case (e.g., callee-saved, static-calls) clobber or set as an input more or fewer registers.
