Messages in this thread | | | Date | Fri, 22 Jun 2007 10:32:11 -0400 | From | "Albert Cahalan" <> | Subject | Re: JIT emulator needs |
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On 6/22/07, Arjan van de Ven <arjan@infradead.org> wrote: > On Fri, 2007-06-22 at 01:56 -0400, Albert Cahalan wrote: > > On 6/21/07, Arjan van de Ven <arjan@infradead.org> wrote: > > > On Fri, 2007-06-08 at 02:35 -0400, Albert Cahalan wrote: > > > > Right now, Linux isn't all that friendly to JIT emulators. > > > > Here are the problems and suggestions to improve the situation. > > > > > > > > There is an SE Linux execmem restriction that enforces W^X. > > > > Assuming you don't wish to just disable SE Linux, there are > > > > two ugly ways around the problem. You can mmap a file twice, > > > > or you can abuse SysV shared memory. The mmap method requires > > > > that you know of a filesystem mounted rw,exec where you can > > > > write a very large temporary file. This arbitrary filesystem, > > > > rather than swap space, will be the backing store. The SysV > > > > shared memory method requires an undocumented flag and is > > > > subject to some annoying size limits. Both methods create > > > > objects that will fail to be deleted if the program dies > > > > before marking the objects for deletion. > > > > > > and these methods also destroy yourself on any machine with a looser > > > cache coherency between I and D-cache.... > > > > > > for all but x86 you pretty much have to do the mprotect() between the > > > two states to deal with the cache flushing properly... > > > > If the instructions to force data write-back and/or to > > invalidate the instruction cache are priveleged, yes. > > AFAIK, only ARM is that lame. > > and your program executes this on all the cpus in the system?
I'll remember that if I ever run a JIT on the SMP ARM box. (there's like one, at the manufacturer, right?)
I don't recall seeing such code in the libgcc tranpoline setup for PowerPC. Either it's not required, or this is a rather popular bug.
Perhaps ARM needs syscalls for this, or emulation for the privileged instructions. This may already exist; it sure is required. So this would be another need for properly supporting JIT emulators. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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