Messages in this thread | | | Date | Fri, 22 Jun 2007 01:56:28 -0400 | From | "Albert Cahalan" <> | Subject | Re: JIT emulator needs |
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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.
For example, PowerPC lets unprivileged code run the required instructions. - 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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