On Sun, Feb 13, 2011 at 7:21 AM, Florian Weimer <f...@deneb.enyo.de> wrote: > * H. J. Lu: > >> On Sun, Feb 13, 2011 at 7:07 AM, Florian Weimer <f...@deneb.enyo.de> wrote: >>> * H. J. Lu: >>> >>>>> Actually, I'm wondering if you can do the translation in user space. >>>>> There already are 32-on-64 implementations in existence, without >>>>> kernel changes (recent Hotspot, LuaJIT, and probably some more). >>>> >>>> Please check out the x32 kernel source and provide feedback. >>> >>> I still don't understand why you need a separate syscall table. You >>> should really be able to run on an unmodified amd64 kernel, in 64 bit >> >> That is done on purpose. x32 is designed for environments where the >> current ia32 API is sufficient. You can think it as ia32 with register >> extended to 64bit plus 8 more registers. Everything else is still 32bit. > > I think of it as amd64 where all the process memory happens to reside > in the first 4 GB of address space, and pointers are stored as 32 bits > (and you'd also reduce the size of longs because sizeof(long) != > sizeof(void *) will break too many programs).
That is what the processor sees in an x32 program. > As I said, both LuaJIT and Hotspot are already using this model, with > custom memory allocators and a user-space translation layers, so I > still don't see what you get by changing the kernel. LuaJIT has even > implemented the amd64 ABI, so you can call C libraries from your > 32-bit code. (Note that LuaJIT uses 64-bit words to store 32-bit > pointers with several tag bits, but it does so even on pure 32-bit > platforms.) They can continue to do so. > If you want to make x32 closer to i386, I don't see the point. Why > would it be problematic if it was as close to i386 as, say, armel? > We are providing a 32bit API with 64bit registers. Current APIs support either 32bit or 64bit. I am not talking about pointer or long. I am talking other types, like time_t, off_t, ..., defined by API. Adding another API is extremely difficult. -- H.J.
